C Trésallet

J L Cardin

J Belghiti

A Cortes

M Richard

E Martinod

Expert witness testimony step by step and how to prepare it

The medical expert witness testimony is a key moment in the pathway of patient complaints as well as in the line of defense of the defendantphysician. For the defendant, it is a difficult time, often experienced as humiliating, because his or her competences are questioned, appraised and discussed in public. However, the defendant must perceive and use this encounter as an opportunity to express his/her viewpoint on the medical accident. This article provides the principal juridical rules that govern the medical expert witness testimony that must be known, as well as some practical advice on how the medical expert witness testimony evolves and how to protect oneself from the complaints, In order to enable the defendant to best prepare for this confrontation between the involved parties

1-Progression of a medical expert witness testimony

A) Prerequisite knowledge

The cornerstone of the medical expert witness testimony is respect for the "sacrosanct" rule that both parties shall be heard in full. However, only information (document, witness…) that has previously been mutually provided to each party can be taken into consideration. In this setting, the elements of the testimony file are said to be inapplicable in the defendant's convocation. The expert asks each party to provide all the documents related to the claim (and in particular, a copy or the original of the entire medical record).

It is not the responsibility of the expert to organize the exchange or the copy of the elements between the parties but to ensure that the exchange effectively takes place. The production of the elements at the time of the final meeting or their transmission only a few days before the encounter is not in favor of transparency and can negatively influence the expert. As soon as the defendant-physician receives the convocation, he or she (or his councilor) should make sure that the medical record is passed on to the expert and the adverse party. One should not hesitate to protest when the opposite party has not respected this exchange of elements (this is often the case of plaintiffs who, when they are treated in another hospital after the medical accident or have asked for a private medical expert witness testimony, have then not passed on all the relative documents to the defendant-surgeon).

For all the recourse circuits, the final mission of all medical expert witness testimonies is to provide the judge (who does not have any medical knowledge!) an enlightened and impartial opinion on the liability implicated and on the damages that warrant compensation. It is not the medical error itself that is condemnable, because errors are always possible even if all precautions have been taken. The condemnation is most often related to a lack of information, lack of means to avoid or prevent the mishap, or negligence.

The designated expert should have the necessary competences in bodily damage evaluation and compensation and, ideally, in the specific specialty under investigation. For evaluation of the injury, there are several specific medical scales and tables do define and quantify injury (Table 1), but there is no consensus as to which one to use, all are deemed valid. The expert should, however, cite which one is used in the final report.

In most cases, the expert receives a typical assignment or mission (Document 1) that includes the questions for which the judge would like to have precise answers. The most widely used list of questions today is derived from the Dintilhac nomenclature (Document 2) [START_REF] Dinthilac | Rapport du groupe de travail chargé d'élaborer une nomenclature des préjudices corporels[END_REF]. The expert is normally required to follow the assignment to the letter. If, however, the expert sees the need to deviate (since the expert is a medical doctor, he or she may have an issue with information or facts that the judge (not a medical doctor) may not have thought of), he or she has to explain why [START_REF] Gachot | Critères de qualité pour une expertise civile réussie: le point de vue de l'expert médecin[END_REF]. It is highly desirable that the defendant-physician be aware of the most frequently asked questions in order to anticipate and prepare the answers. This means that as soon as the defendant-physician receives the assignment, he or she should read it carefully before transmission to the councilors or advisors.

The judge, as well as the conciliation and compensation board (CCB) are not required to follow or adhere to any of the opinions of the expert, but will be more attentive to the evaluation of bodily damage than to the potential allocation of responsibility.

The judge expects the expert to provide a scientific analysis of the facts, nothing more. The judge does not want the expert to give his or her opinion of the juridical aspect of the case, for which the expert has neither the competence nor the mission. The expert is therefore not supposed to give any advice as to the fault but only on any lack of adherence to the accepted state-of-the-art, medical error or loss of chance. The judge has to qualify the expert's report from a juridical viewpoint and decide whether the management by the defendantphysician was faulty or not [START_REF] Richard-Piauger | l'expertise en responsabilité hospitalière dans le secteur public : l'exemple de l'APHP. Médecine et droit 2016 et al[END_REF].

B) Convocation

As soon as the expert is designated, he or she fixes an appointment by registered mail, return receipt requested, addressed to all parties concerned. Usually, the expert decides on the final date and time according to the availability of each party, contacted beforehand as needed. The date and venue of the meeting are given (in general the office of the expert or the residence of the patient if the latter is not ambulatory). Any change of date is usually difficult and to avoid any dissent or controversy, the expert should propose several potential dates, sufficiently spaced out, in the letter. The date that receives the most common approval is the one chosen and then the convocation should be sent out to all parties, at least three weeks before the date of the encounter.

Any of the parties has the possibility to demand the recusal of an expert, if the expert does not recuse himself or herself, in case of a conflict of interest between the expert and one of the parties. This recusal can be difficult, because it is not necessary that the expert's specialty be the same that is concerned by the prejudice. If there is any conflict of interest, a conscientious and fair expert should ask for help from another expert, who is a specialist in the particular field under scrutiny. In complex cases, several co-experts can be involved.

C) The participants

The expert:

The expert is responsible for the testimony meeting that he or she presides personally. The expert should be independent and impartial.

The expert must ensure that the principle that all parties shall be heard is respected and therefore gather the versions of everyone concerned. The expert must be involved in all discussions. The parties should not communicate directly with each other. The expert should not communicate directly with the plaintiff or representatives or, worse, berate them. The expert has the responsibility of ensuring that all discussions are calm and dispassionate [START_REF] Gachot | Critères de qualité pour une expertise civile réussie: le point de vue de l'expert médecin[END_REF].

The defendant-surgeon:

The defendant's presence is desirable but not mandatory; the defendantsurgeon can be represented by a lawyer or physician-advisor. However, failure to appear is seen unfavorably and no one else can better explain the management plan, how the events occurred or the reasons that led to the prejudice under investigation. To the patient as well as the patient's family, the surgeon-defendant's presence attests that the physician is not shunning the affair or shying away from any responsibility [START_REF] Manaouil | Mise en cause du chirurgien : quelles sont les procédures ? Comment gérer une expertise ?[END_REF]. The defendant should be accompanied by a physicianadvisor designated by his or her insurance company if the defendant is in the private sector or by the hospital or health-care establishment if the defendant is employed. It is often preferable that the physician-advisor take the active part in the discussion to avoid any tension between the parties, and that the defendant only answer any question that was directly posed by the expert or that the defendant intervene only when the details are something that only the defendant can know about or explain. The physician-advisor should study the case in depth and draft a list of the main elements upon which it is important to defend his or her colleague. This "internal" pre-report is often requested by the insurance company, ideally, after the defendant has reviewed and amended it as necessary. This report should be as precise as possible and include the shortcomings of the case in order to be prepared to counter any attack or anticipate any question that might weaken the defense (most often these concern the absence of proof that all necessary information was provided to the patient).

The victim (or beneficiary)

The presence of the patient or beneficiary is mandatory during the audience (the obvious exception being when the patient is deceased), as much to hear his or her version of the facts and complaints as to evaluate the damages by the clinical examination. The patient is generally assisted by a physician-advisor or substitute (family physician or physician appointed by the insurance company). More and more frequently, patients are also accompanied by a lawyer, even in out-ofcourt settlement discussions, which is not at all mandatory except in the presence of a judge. The defendant should not be destabilized by the interjections, sometimes violent or unfair from the lawyer, whose trade is to argue or even to provoke. Once again it is the expert's responsibility to make sure that the discussion remains dispassionate. The expert is required to answer only those questions that are related directly to the mission [START_REF] Gachot | Critères de qualité pour une expertise civile réussie: le point de vue de l'expert médecin[END_REF]. However, if something is missing, after agreement by the parties and counselors, and in particular by the patient, responses to questions that were not planned can be posed and answered.

D) Medical expert witness testimony o Statement of facts: file documents

The medical testimony begins with the expert's statement of fact, as precise and detailed as possible. This supposes that the expert has received and reviewed the totality of the documents in the file, auxiliary (nurse orders) notes as well as all complementary studies. The clinical history is open to all the parties, underscoring the importance for the defendant and advisor to know the case as best possible to be sure that nothing of importance was left out. It is important that everyone who has something to say, speak out, whether to complete the history, or produce any document that could have escaped the attention of the expert: past medical history susceptible of explaining certain complications such as diabetes, tobacco or alcohol abuse, anticoagulation medication, steroids, previous surgeries…), but also documents of informed consent, complementary investigations or other significant data … The defendant's attitude should be both neutral and empathetic. And certainly the defendant should not adopt any casual attitude: phrases such as: « I do not remember …. It is my lawyer that takes care of that; I have already lost enough time with this affair… » are out of place.

Everyone should be heard without any shortcoming, but people should be asked to speak before they take the floor; answers should be convincing, brief and above all, answers should be thoughtful. There have been several instances when one word too many at the end of the session (when the tension has fallen, and this is what the patient's lawyer has been waiting for!) unfavorably revives the debate. Faced with such dramatic events, it is good to have some humane and compassionate words to address to the patient or family at this moment.

Having nothing to say to a mourning family does not appease and will irritate more than one of the most neutral experts.

The stumbling points which surgeons often have to deal with are almost always the same: absence of proof of consent or traceability of information given to patients, absence of a letter to the family doctor, disorganized or faulty keeping of patient records, laconic operative reports without adequate details, absence of a discharge summary, lack of, or ignored complementary investigations, incomplete or contradictory prescriptions.

Preparing for the testimony session means being able to address and answer each and every weak point of defense that the physician-advisor was able to detect beforehand with the defendant. factual review is also a good time to underscore some teaching points for the expert as well as for defendants. It is regrettable when adequate information and explanations of possible complications were not provided to patients during their hospitalization. Effectively patient complaints are frequently the result of faulty pre-and post-operative communication. It is assuredly difficult to explain to a patient why a complication occurred, especially a severe complication, but such an explanation allows to defuse most conflictual situations and thus to avoid getting into contentious situations [START_REF] Manaouil | chirurgie bariatrique : pas de légèreté dans la prise en charge des suites opératoires[END_REF]. Absence of explanations during hospitalization is always a source of misunderstanding, and may generate suspicion that information has been concealed. This can even generate hostile reactions.

It is not that rare for experts to hear that patients and/or families open a medico-legal procedure simply to obtain an explanation and rather than to benefit from some form of compensation.

Again, let it be said that surgeons are obliged to inform their patients of any damage or serious undesirable event within 15 days of onset. This obligation is the same as when the patient thinks he or she has been the victim of damage due to a health care procedure (article L-1142-4 of the French public health code) [START_REF] Has | Annonce d'un dommage associé aux soins[END_REF].

Medical examination of the patient

This examination is performed in the presence of all physicians. The plaintiff's lawyer can be present if the patient so desires. The examination is fairly straightforward but all details must be noted, even the most banal: surgical scars, drains (length, width, material), incisional hernia, spontaneous pain or pain with palpation, gait, handicaps,… This is also the moment to point out that one or another scar is unrelated to the operation under investigation, and to ask the patient if there are any further damage that was not taken into consideration in the initial statement: incontinence, sexual sequelae…

The goal of this examination is not to reveal any fault or error but simply to identify the damages that could lead to compensation.

Discussion

The expert has to answer several different questions according to the mission that the magistrate or the CCB may have requested. Thus, further deliberations will center on identification of one or several complications, the existence of damage (constituted by the totality of damages sustained by the patients or indirectly by the beneficiaries), and to then establish if there is a causal link between the damage and any problem in the management of the patient. Based on this medical (and not juridical) discussion, the magistrate will decide whether the damage is related to a fault (fault-related medical accident) or a random therapeutic accident (non fault-related medical accident).

In practice, most discussions and disagreements are based on the same questions: could the patient's previous status (past medical history) contribute to or be partly responsible for the complications? Was the information provided clear and fair? Did the operative indication follow current recommendations? Were the standards of state-of-the-art care respected?? Was post-surgical care scrupulous and well organized?

Were all available means and resources well used?

Preparation for the medical expert testimony means being ready to answer all these questions precisely, without hesitation, and to support these arguments (cf. infra : how best protect oneself from complaints).

The expert should not take sides with either party but rather to record each party's arguments. This discussion can sometimes be stormy because emotions often override reason and the plaintiff wants to see the surgeon convicted (with consequences) while the defendant seeks exoneration. Once again it is the role of the expert to avoid any and all overflow of emotions or outbursts of temper and to ensure that everyone has an equitable time of discourse.

Medico-legal work-up

The Dinthilac nomenclature [START_REF] Dinthilac | Rapport du groupe de travail chargé d'élaborer une nomenclature des préjudices corporels[END_REF] has allowed harmonization of assessment tools, definitions and avoids the use of certain abbreviations or acronyms that could lead to confusion. (for example, ITT in French, could be interpreted by some as "interruption totale de travail" (complete lay-off from work) or "interruption temporaire de travail" (temporary lay-off from work…), and should therefore be avoided. Use of the Dinthilac nomenclature is strongly recommended, whether the legal instances be administrative or judiciary.

This part of the testimony is meant to help the judge evaluate the consequences of damage, which otherwise might be outside his or her competence. This underscores that precision in the evaluation is of utmost importance because often the judge will use the terms as written, and this will then be used by the victim to exercise his or her compensation rights to the third-party payers (care facility, CCB, insurance company, social security benefits…) item by item.

The Dinthilac nomenclature includes 26 items of possible damage to the victim, 20 "direct" and six "indirect" (Document 2).

The classification distinguishes between "economic losses" (debt or reparation or financial benefits related to the damage that can be evaluated according to a financial scale) and "non-economic losses"

(not convertible into money, and therefore non-transmissible). Damage is evaluated according to whether the losses are temporary or permanent.

The transition between the two periods, determined by the expert, is the consolidation date which fixes the end of the disease. This should not be confused with recovery. Consolidation means the health status of the patient is judged stable with possible sequelae, while recovery means a return to the patient's anterior status, before the damage.

Lastly, the general principle of compensation rights is full compensation.

Of importance, the judge has to make sure that compensation is not a source of enrichment for the victim.

Conclusion: At the end of evaluation, the expert asks all parties if they have anything to add to what has been set forth in the original mission.

The discussion is first opened to the plaintiff, by virtue of priority to the victim. The expert is not required to make his or her final conclusions known but, usually, by custom, provisory conclusions are presented, although the expert does not have to pronounce himself or herself on the possibility of fault or not.

2-Medical expert testimony [2].

This report is obviously the key element to which all parties must refer afterwards and upon which the judge makes his or her decision. This report must be written with extreme rigor; the expert must make sense of the exchanges. The order of the paragraphs should be the same as in the initial discussion or interpretation of the facts; otherwise the parties can obstruct or contest the process. Every word counts. The expert must above all not delve into any juridical interpretation, as is all too often the case. This is within neither the expert's competence nor charge. In particular, the expert does not need to state whether there was a fault committed or whether the damage was due to bad luck (random therapeutic accident). Only the judge is authorized to make any medicoscientific analysis of the expert's report.

From this report, the judge expects to be able to determine whether there is any causal link:

between the action under scrutiny and onset of a complication between the complication and onset of damage between any flaw somewhere along the line of management and onset of damage

The argument of the expert must repose on scientific notions, validated or not, and not on personal opinion. For example, to explain that the complication is not normal after a surgical operation, the expert should refer to the medical literature and the standard of care in the specialty considered. To explain a potential flaw, the expert should refer to the consensus or recommendations current at the time of the accident.

Evaluation of the loss of chance to avoid a complication, usually statistically debatable, does not make any sense without sound and published references.

In most instances, a pre-report is sent to all parties, with an interval for answers to questions or any comments, generally within four weeks after reception. The expert must respond to these comments in his or her final report, optionally in an annex.

If the expert does not want to provide a pre-report, he or she must say so clearly at the end of the testimony session and give his or her conclusions so that the parties can react and retort as necessary, in writing, before the definitive report is composed.

It is always possible to contest a report, even in its definitive version, whenever one believes that something has not been respected in the debate, that the analysis was not impartial, that causality was established (or not) according to the expert's opinion and not in accordance with scientific data.

The judge is not obliged to abide the expert's technical analysis. If the judge believes that he or she has not been informed clearly or that the claim is not well-founded, he or she can ask for a complementary or counter expert testimony.

3-How best to protect oneself from complaints… and be prepared for a medical expert witness testimony

Protection against complaints or at least limiting the risks of complaints is possible as long as the health care pathway of all patients is controlled with rigor. Although damage occurs more frequently in certain specialties where exposure to complications is higher (orthopedics, emergency surgery, visceral surgery), complaints arise more often in units where the physicians and/or the personnel are poorly organized. Prevention of complaints does not only repose on individual discipline, a prerequisite for all surgeons who want to reduce the number of complaints, but also relies on irreproachable organization, and collective management of patients.

Following are the most frequently noted organizational or functional short-comings advanced by experts (and law courts):

3.1: Medical file poorly kept or not kept at all:

-When medical notes mentioning the complications(s) under scrutiny and/or their management are lacking, it is difficult to maintain that the complication was reversible or corrected so quickly that it was not deemed necessary to note it down. During his or her investigation, the expert must often refer to nurses' notes and transmissions, often the only way to correctly reconstruct the chronology of events during patient management. Alarmist nursing notes when the medical file is silent have unfavorable consequences for the surgeon. Written prescriptions reflect without question the ideas or intentions of the physician but do not prove that the patient was adequately assessed.

-A laconic or worse, missing operative report (OR) and/or discharge summary are heavily penalizing. It is quasi impossible to pretend that the decision to operate was justified and that the standards of care were respected if the OR is missing or inadequate (one in which the description of lesions was inadequate). The OR is the main document which the expert will use to determine whether a "fault" was committed or not and the key element with which the surgeon will be able to defend his or her good practice. Any OR that is altered or inauthentic will be severely judged, especially when the revisional surgical procedure is performed in an expert center that highlights the fallacy of the initial document.

-Complementary investigations that are not entered into the medical record, damaged or not retrieved, attest to a lack of diligence. It is obvious that every time a physician orders a complementary study, it is his or her obligation to retrieve it, interpret it and act on it accordingly. Effectively, not being able to find a CT scan or the result of a urinalysis, for example, can be used by the plaintiff to point out negligence or a delay in appropriate management. It will then be difficult for the defendant to affirm that the after-care of the patient went according to the rules if the complementary investigations are not entered or incomplete. Likewise, it will be difficult to defend the loss of chance if these investigations are missing.

-Illegible, contradictory, or missing prescriptions are very penalizing.

Prescriptions will be examined in minute detail, since they can easily be traced hour by hour in our electronic age, and compared to the paramedical notes. The expert should check the existence of therapeutic protocols for thrombophlebitis prevention, pressure sores, management of naso-gastric tubes, surveillance protocols…

The indications for prescriptions as well as how they are kept and followed are an excellent indicator of the organization of a service.

The traceability of all prescriptions and administration of all medications is a reflection of good coordination between the medical and paramedical teams, and therefore the absence of negligence.

In order to defend oneself before the expert, it is judicious to:

-Transfer a complete copy of the patient file, wisely selected and well ordered after collecting all the complementary investigations.

Providing a bulky patient file that is totally out of order will have a disastrous effect on the testimony. The form of the file is often the reflection of its content, and also attests to the quality of management.

Give details on the patient pathway, highlighting those aspects of care that come from protocol and underscoring the quality of care by demonstrating the good coordination of all members of the medical and paramedical team as well as good collective and permanent surveillance.

3.2-Missing pre-operative information:

The plaintiff or his or her lawyer nearly always attack the surgeon on this point although this is easily avoidable. Missing information is often the first notion the expert looks for in the patient file. From the legal viewpoint, providing clear and fair pre-operative information is equivalent to allowing the patient to avoid the complication by having the possibility to refuse the proposed surgical act, or to discuss possible alternatives. Therefore, if there is no trace of information provided to the patient in the file, the expert will have to take note of this lack of information, and the judge will consider that this missing information constitutes a severe prejudice and a fault, even if the indication was perfectly legitimate or even indispensable. The absence of traceability of If information provided to the patient or close relative is absent or untraceable, it cannot be admitted in testimony, even if the surgeon asserts in all honesty that he provided this information orally.

Moreover, the information has to be given fairly: a signed form on the same day as the pre-operative consultation is practically equivalent to an absence of any time for reflection. Conversely, a delay of a few weeks between the consultation and the operation, especially a risky operation,

gives the patients ample time to ask for complementary information if so desired, or to request advice from other physicians or care-givers. A vague and impersonal consent form, even if signed by the patient, is not any proof that the patient has understood the contents or the real risk stratification.

Failure to inform the patient with regard to complications:

Even if this may seem difficult, painful, or even humiliating (a blow to surgical ego…), it is essential for the surgeon to communicate with the patient immediately, clearly and in a straight-forward manner, when a complication arises. This is the best way to show that you are in control of the situation and that you assume your responsibilities. Shying away from questions or avoiding a rendez-vous solicited by the patient is the best way to increase the suspicion that you are trying to conceal a "medical error". It will soon be made evident in the testimony that the plaintiff(s) have made extensive notes, including the most insignificant, on what has not gone according to the book. They will search for the least dysfunction to strengthen their argument that errors have been committed somewhere within the team of care-providers and that they are being concealed: a resident who forgot to prep the patient's skin with an alcoholic solution (therefore leading to infection?), a care-giver who made a mistake in the meal tray given to the patient who was supposed to be on a salt-free diet (therefore leading to pulmonary edema?) just to name a few …. [START_REF] Manaouil | chirurgie bariatrique : pas de légèreté dans la prise en charge des suites opératoires[END_REF]. Shying from this responsibility will always be seen as faulty after-care and negligence. In case of difficulty in communication (hostility or loss of confidence by the patient or close relatives), it is important to rapidly hand over management to a colleague or hierarchic superior and trace the conflict in the most neutral and factual manner possible. Lastly, transfer of the patient to a medical center is another alternative that should be offered before the patient or his close contacts so make the demand.

In order not to fall into the easy trap of lack of information given to the patient, there are a few simple solutions that must be in your daily reflection.

That the information was given must be perfectly legibly traced in the file: -during the expert witness testimony preparation, prepare all the necessary documents proving that this information was delivered.

It is not rare that the expert's report is terminated or considerably shortened as soon as this information is made available. In the absence of written evidence, neither the expert nor the judge are held to believe the spoken word.

3.4-Non-justified or abusive operative indication

A large part of debate during expert testimony preparation is related to the pertinence of the indication for surgery. For some experts, this is even the first item they want to find in the patient file. Even if it appears to be completely up to the defendant surgeon, the expert has to dissect the indication implicated in the accident. The reasons why this or that operation was chosen should be clearly explained and traced in the file and letters of correspondence. The indication will be all the easier to defend if it has been approved in a multi-disciplinary meeting (oncology or bariatric surgery, for example) or during the staff workup. Any alternative proposed to the patient must also be mentioned (surgical abstention and its consequences, possibility of medical treatment or not).

It is unacceptable to hear a surgeon plead that this or that operation was decided because "this is what we usually do" or "every surgeon does the same in this situation". It is essential that the expert does not get the feeling that the indication for surgery was posed lightly, arbitrarily, automatically or worse, recklessly. Any non-justified surgical intervention is severely penalizing for any defendant in this setting.

To best defend oneself during the preparation of an expert witness Experts, even though rarely in the same specialty, will have no problem in recognizing a good indication if it is based on high quality scientific literature (evidence based medicine).

Technical error

For the plaintiffs as for the expert, one possible explanation for a complication is a technical error or blunder. The operative report has to be sufficiently detailed in order for the surgeon to defend himself or herself. The concept of surgical "blunder" is fuzzy and often used by experts who do not have surgical knowledge. It must be explained during the final meeting with all parties concerned that certain complications are classical, even if rare, if only because of the exposure to risk of one or another organ during surgery. For example, it would be unacceptable to pretend that post-thyroidectomy recurrent nerve palsy was a "blunder" because it is recognized that the nerve is at risk in this procedure and the anatomy of the nerve should therefore be known and recognized. Likewise, it must be shown during the expert testimony workup that all available means had been used to arrive at the correct diagnosis.

Claiming that the CT scan or blood test was not available for one reason or another does not clear the surgeon of any responsibility. If the facility does not have the correct means available, the patient should be transferred to a facility where the desired investigation or blood test is available.

To best defend oneself:

It is not the medical error itself that leads to condemnation because "random" errors occur even when continuous precautions have been taken; lack of means or negligence in their use or indication are condemnable.

It must therefore be shown that the surveillance was attentive, conscientious, weIl-organized and recorded.

One must be able to justify that, if an investigation was ordered late, it was because there was no clinical or laboratory evidence to support ordering it earlier and that the result was taken into account accordingly.

Conclusion:

To be « accused », irrespective of the type of judicial venue chosen by the patient, is often a traumatizing experience for the defendant surgeon or caregiver team. Even if the claim can initially seem to be unfair, this can be a time for the care-providers to revisit how patient care is organized and the means of communication with patients. One of the first steps is full involvement of the surgeon in morbidity and mortality conferences.

Oral and written communication deficits are often the source of litigation that could have been avoided during the hospitalization of the patient.

One must know that the judge will first listen to the victim and refer to the expert witness testimony; the defendant must prepare for the testimony well upstream to justify the management and to have appropriate support from medical counselors, lawyers, jurists, colleagues, in order to brave this often afflictive trial. The surgeon should not shy away but, to the contrary, show that he or she assumes his or her responsibilities and decisions that were taken for the better of the patient. It is important to take into consideration setting the expert witness testimony is presented in (out-of-court settlement, law court…), to prepare one's defense knowing all the details and above all those that are specifically the objective of questions that will be posed to the expert. During the investigation, one must not give in to provocation, but remain calm and empathetic, answer all questions posed without aggressiveness and with a sound scientific basis. Patient records that are complete and well-kept are easy to defend. One must not forget that many patients (or beneficiaries) search for explanations that they did not get during the management period. Finally, there are true post-operative damages that warrant compensation whether they result from faults or not (and are compensated by the insurance companies). Defendants should show themselves cooperative during the investigation, and not be constantly on the defensive, and must try to maintain the bond of confidence that led the patient to choose the surgeon.

PLAN 1

 1 Progression of a medical expert witness testimony -A Prerequisite knowledge -B Convocation -C The participants -D The medical expert witness testimony o Statement of facts: file documents o Medical examination of the patient o Discussion on the damages o The liability estimation o Conclusion 2 The medical expert witness testimony report 3 How to protect oneself against a complaint and prepare for the expertise 4-Conclusion

a

  letter should be sent to the family or the family physician (it is important to indicate in the letter the presence of family members or other persons present at the time of writing), and the information should be indicated directly in the patient file as proof that a drawing of the operation with explanations as needed was provided (a copy should be in the file), an informational brthe HAS recommendations for bariatric surgery), and informed consent for the specific operation under consideration should be signed by the patient. Of importance -inform the patient or close contacts immediately of any complication and keep them informed regularly of the evolution.

  testimony session:It is necessary to check that the operative indication corresponds to the recommendations of Learned Societies or agencies recognized as an authority (French High Authority of Health (HAS), French National Institute of Cancer (INCa)…) at the time the indication was posed to the patient. In the absence of consensus, the decision should be based on sound references found in the literature (high impact factor journal or journal recognized in the specialty). The indication has to be explained to the patient and in the letters written during the consultation, with a request for an outside opinion if necessary, and a reasonable delay for reflection before taking any decision.

Faulty follow-up, or failure to rescue, delay in diagnosis and treatment

  Plaintiffs often claim that if their complication has been detected earlier, they would not have sustained the same damages. Only a well-kept medical file, in which one finds all the investigations ordered, retrieved, interpreted and acted on, offers any possibility of defense. A delay in diagnosis can be justified if one finds that all was in order every day preceding the diagnosis. Conversely the absence of written notes during the hospitalization is indefensible. All physicians have the right to leave the hospital or care facility but they must ensure the continuity of care for their patients. It is impossible to justify that the surgeon was away, and the patient was only under the surveillance of nurses. As said above, it is

	an operation. The particular operative technique should be justified by
	the Learned Society recommendations, authoritative textbooks or
	references.
	3.6 inadmissible that a paraclincal investigation be ordered but only
	interpreted 48 hours later.
	To best defend oneself during the testimony preparation, the surgeon
	should know the acknowledged rate of and type of complication of the
	operation under investigation by supportive data (data repositories,
	monographies of Learned Societies, references in the literature…). It is
	important to state one's experience with the type of operation under
	investigation, and if necessary, the number of the same type of
	operations performed previously, or the number of years performing such

These types of dysfunctions are always qualified as faulty surveillance and negligence responsible for delays in diagnosis and treatment.

Table 1

 1 Medical scales used in France

	Concours médical 2001
	Société Française Médecine Légale (SFML)
	Association des Médecins Experts en Dommages Corporels
	(ANAMEVA : Association Nationale des MEdecins experts de Victimes
	d'Accident)
	Association pour l'Etude de la Réparation du Dommage Corporel
	(AREDOC))


Keywords: Laparoscopic liver resection, colorectal liver metastases, open approach, postoperative outcomes, survival Résection hépatique laparoscopique, métastases hépatiques d'origine colorectale, laparotomie, suites postopératoires, survie

Highlights, limitations and future challenges of laparoscopic resection for colorectal liver metastases Points clés, limites et défis futurs de la résection laparoscopique des métastases hépatiques d'origine colorectale Running head: Laparoscopic approach in colorectal liver metastases. Titre courant : Résection laparoscopique des métastases hépatiques d'origine colorectale.

INTRODUCTION

Colorectal cancer is the third most common cancer and the third leading cause of cancer deaths in Western countries [START_REF] Siegel | BCancer statistics[END_REF]. In France, [START_REF] Karakousis | Laparoscopic versus open gastric resections for primary gastrointestinal stromal tumors (GISTs): a size-matched comparison[END_REF].000 new patients develop colorectal cancer every year. The liver is the most common organ targeted by colorectal cancer metastases (CRLM), representing almost 50% of metastases. Approximately, 15-25% of colorectal cancer patients have synchronous CRLM at initial workup, and 20-30% patients developed subsequent liver metastases within few years following diagnosis [START_REF] Manfredi | Epidemiology and management of liver metastases from colorectal cancer[END_REF]. Despite huge advances in chemotherapy and targeted therapy for colorectal cancer, liver resection is still the only potential curative treatment for patients with CRLM whereas advances in surgical techniques and perioperative care have decreased the 30-day mortality of liver surgery from 24% in 1970 to less than 2% presently [START_REF] Gilg | Mortality-related risk factors and long-term survival after 4460 liver resections in Sweden -a population-based study[END_REF]. A large number of studies reported that hepatic resection for CRLM provided favorable long-term survival, with 5 year and 10 year survival rates ranging from 33 to 58% and 23 to 39%, respectively [START_REF] Cannon | Laparoscopic versus open resection of hepatic colorectal metastases[END_REF][START_REF] Beppu | Long-term and perioperative outcomes of laparoscopic versus open liver resection for colorectal liver metastases with propensity score matching: a multi-institutional Japanese study[END_REF]. In addition, a worldwide survey indicated that the long-term survival of patients with CRLM who underwent one to four liver resections due to hepatic recurrence was almost similar [START_REF] Adam | Liver resection for colorectal metastases: the third hepatectomy[END_REF].

Although laparoscopic surgery for colorectal cancer has been largely evaluated and widely used [START_REF] Bonjer | A randomized trial of laparoscopic versus open surgery for rectal cancer[END_REF], laparoscopic liver resection (LLR) has developed more slowly than other fields of laparoscopic surgery [START_REF] Ciria | Comparative sort-term benefits of laparoscopic liver resection: 9000 cases and climbing[END_REF]. The purpose of the present update was to identify factors limiting widespread acceptance of laparoscopic approach, and to underline benefits and limits of LLR, together with the oncological relevance of LLR in CRLM.

WIDESPREAD ACCEPTANCE OF LAPAROSCOPIC APPROACH

Diffusion of laparoscopic approach in abdominal surgery

Historically, open surgery through laparotomy was the standard approach for abdominal procedures. Laparoscopy is a mini-invasive approach that allows performing abdominal procedures through small incisions with the help of a camera. Initially developed during the late 1980's for cholecystectomy, laparoscopy was progressively adopted for various abdominal oncologic and functional procedures during the last three decades. In this setting, a significant number of wellconducted randomized trials have demonstrated that the laparoscopic approach was associated with improved postoperative outcomes in various upper and lower gastrointestinal procedures including colorectal resections and esophageal resections without jeopardizing the oncologic outcomes of the patients.

Diffusion of laparoscopic approach in liver surgery

The first successful laparoscopic liver resection was reported in 1993, but the diffusion of laparoscopy in liver surgery has long been limited due to initial technical limitations (absence of specific laparoscopic devices for liver surgery), concerns regarding the safety of the patients (risk of gaz embolism or uncontrollable hemorrhage), doubts on the oncologic safety of the approach (risk of incomplete resection in segments of difficult access) and a long learning curve (since an expertise in both liver and laparoscopic surgery is needed). Hence, it is only in the early-mid 2000's that first large series reporting the safety and feasibility of laparoscopic liver resection were released. According to the French Registry, 5 300 hepatectomies were performed in 2005 and it increased to 7 800 in 2006, with a significant increase of "atypical" resections (1 500 atypical resections in 2005 compared to 3 500 atypical resections in 2006). Among these liver resections, the number of LLR increased from 550 in 2005 to 1 100 in 2006 (respectively 10% and 16% of all hepatectomies) [START_REF] Farges | ACHBT-French Hepatectomy Study Group. Incidence and risks of liver resection: an all-inclusive French nationwide study[END_REF].

Limits of laparoscopic approach in liver surgery

Indeed, the laparoscopic approach of the liver does not allow the same access to the liver as the open approach, the anterior segments being easier to access to. Thus, some elementary open approach gestures such as liver palpation and mobilization, or vascular control and parenchymal transection may be challenging for an unexperimented laparoscopic liver surgeon. Vigano et al. suggested that a threshold of 60 cases was necessary in the learning curve for both minor and major LLR [START_REF] Vigano | The learning curve in laparoscopic liver resection: improved feasibility and reproducibility[END_REF]. More specifically to CRLM, the fear of both involved resection margins and tumor dissemination at the trocar sites with a potential influence of the pneumoperitoneum have been initially reported by several authors [START_REF]Laparoscopic liver resection[END_REF]. However, many series challenged this assumption and this rare situation was described only in case of massive tumor spillage [START_REF] Ciria | Comparative sort-term benefits of laparoscopic liver resection: 9000 cases and climbing[END_REF][START_REF] Fretland | Laparoscopic Versus Open Resection for Colorectal Liver Metastases: The OSLO-COMET Randomized Controlled Trial[END_REF]. These different factors may have limited the development of the laparoscopic approach in the treatment of CRLM.

However, the development of new techniques and dedicated instruments has gradually allowed the diffusion of laparoscopic approach (13) and to date, more than 9 000 laparoscopic liver resections have been performed and both feasibility and safety of this approach are now largely accepted [START_REF] Ciria | Comparative sort-term benefits of laparoscopic liver resection: 9000 cases and climbing[END_REF].

Difficulty of laparoscopic liver resection

Some cases of LLR are widely accepted to be simpler, whereas others are more technically demanding [START_REF] Buell | World Consensus Conference on Laparoscopic Surgery. The international position on laparoscopic liver surgery: The Louisville Statement[END_REF][START_REF] Wakabayashi | Recommendations for laparoscopic liver resection: a report from the second international consensus conference held in Morioka[END_REF]. Therefore, it was necessary to gradually increase skills of LLR according to the experience level before performing technically demanding procedures. For a safe diffusion of LLR, a clear training pathway was needed based on the assessed difficulty of particular procedures within the broad spectrum of LLR. However, whatever the surgical approach, the difficulty of a surgical procedure is hardly assessed, because its definition is subjective. A recent study by Ban et al. has attempted to assess surgical difficulty of LLR through a score using multiple variables such as tumor location, tumor size, proximity to the major vessels, or liver function [START_REF] Ban | A novel difficulty scoring system for laparoscopic liver resection[END_REF]. Even though this scoring system can be used in the preoperative period, it remains complex to integrate all these variables in an objective prediction of technical difficulty.

In 2017, the group of the Institut Mutualiste Montsouris proposed a new classification to stratify the difficulty of LLR based on objective intraoperative variables including operative time, blood loss, and conversion rate [START_REF] Kawaguchi | Difficulty of Laparoscopic Liver Resection: Proposal for a New Classification[END_REF]. In this stratification of LLR difficulty, Group I represents the first level and includes wedge resection and left lateral sectionectomy. Group II represents the intermediate level with anterolateral segmentectomy and left hepatectomy. Last, Group III represents the highly advanced level including posterosuperior segmentectomy, right posterior sectionectomy, right hepatectomy, extended right hepatectomy, central hepatectomy, and extended left hepatectomy.

Procedures in Group I should not be considered as ''easy,'' but less technically demanding and less difficult than other LLR. Thus, Group I procedures should be suitable for liver surgeons at the beginning level of LLR. This classification was expected to serve as a guide determining whether laparoscopic approach can be used, depending on the surgeons' technical levels. In addition, it can be helpful for reducing the potential risk caused by technically demanding LLR procedures that are beyond the surgeons' technical levels.

BENEFITS OF LAPAROSCOPIC LIVER RESECTION IN CRLM

Several studies has highlighted the added values of LLR versus open liver resection (OLR) in terms

of reduced blood loss, lower morbidity rate, shorter length of hospital stay and earlier return to functional activities [START_REF] Castaing | Oncologic results of laparoscopic versus open hepatectomy for colorectal liver metastases in two specialized centers[END_REF][START_REF] Hasegawa | Long-term outcomes of laparoscopic versus open liver resection for liver metastases from colorectal cancer: a comparative analysis of 168 consecutive cases at a single center[END_REF][START_REF] Karagkounis | Perioperative and oncologic outcomes of minimally invasive liver resection for colorectal metastases: a case-control study of 130 patients[END_REF][START_REF] Qiu | Laparoscopic hepatectomy is associated with considerably less morbidity and a long-term survival similar to that of the open procedure in patients with hepatic colorectal metastases[END_REF][START_REF] Schiffman | Laparoscopic versus open liver resection for metastatic colorectal cancer: a meta-analysis of 610 patients[END_REF][START_REF] Tohme | Minimally invasive resection of colorectal cancer liver metastases leads to an earlier initiation of chemotherapy compared to open surgery[END_REF][START_REF] Topal | Outcome of laparoscopic major liver resection for colorectal metastases[END_REF]. Moreover, other advantages including less tissue damage, surgical stress, and overall costs have also been reported [START_REF] Polignano | Totally laparoscopic strategies for the management of colorectal cancer with synchronous liver metastasis[END_REF][START_REF] Vanounou | Comparing the clinical and economic impact of laparoscopic versus open liver resection[END_REF]. Two randomized controlled trials comparing open and laparoscopic approaches in liver resection have been conducted.

Unfortunately, the first one (Orange II, NCT 00874224) was stopped after failing to recruit patients [START_REF] Wong-Lun-Hing | Randomized clinical trial of open versus laparoscopic left lateral hepatic sectionectomy within an enhanced recovery after surgery programme (ORANGE II study)[END_REF]. The second one « Oslo CoMet trial (NCT01516710) » was completed (n=280) and demonstrated a significantly lower 30-day complication rate in the laparoscopic-surgery group compared to the open-surgery group (19% vs. 31%) [START_REF] Fretland | Laparoscopic Versus Open Resection for Colorectal Liver Metastases: The OSLO-COMET Randomized Controlled Trial[END_REF]. However, only patients undergoing minor resection for less than 4 lesions were selected and no survival analysis was performed. Short-term outcome results of comparative series of laparoscopic versus open resections of CRLM are detailed in Table 1. Interestingly, In the study of Vanounou et al., the economic impact of the laparoscopic approach was noteworthy, with the laparoscopic approach US$1527-2939 more cost efficient per patient compared to the open technique [START_REF] Vanounou | Comparing the clinical and economic impact of laparoscopic versus open liver resection[END_REF].

A theoretical advantage for LLR is reduced blood loss due to the increased intra-abdominal pressure counteracting venous bleeding from the liver [START_REF] Wakabayashi | Laparoscopic hepatectomy is theoretically better than open hepatectomy: preparing for the 2nd International Consensus Conference on Laparoscopic Liver Resection[END_REF]. This difference in blood loss and transfusion requirement may be related to the magnified images allowing a more meticulous dissection, the pneumoperitoneum, and a decreased blood loss from the abdominal wall provided by laparoscopic approach [START_REF] Kazaryan | Laparoscopic resection of colorectal liver metastases: surgical and long-term oncologic outcome[END_REF]. Indeed, the hemostatic effect of the intra-abdominal pressure induced by the pneumoperitoneum and the magnified view in laparoscopy may allow surgeons precise identification and management of vasculobiliary structures [START_REF] Makabe | Efficacy of occlusion of hepatic artery and risk of carbon dioxide gas embolism during laparoscopic hepatectomy in a pig model[END_REF]. However, while most of retrospective series reported a benefit of laparoscopic approach on blood loss, the first and only randomized controlled trial published about LLR versus OLR of CRLM did not observe a significant difference regarding the intraoperative blood loss and showed a similar rate of transfusion (8%) in both arms [START_REF] Fretland | Laparoscopic Versus Open Resection for Colorectal Liver Metastases: The OSLO-COMET Randomized Controlled Trial[END_REF]. In a recent series, Tomimaru et al. reported the first series questioning the validity of intraoperative blood loss measurement through suction of the blood accumulated in the abdominal cavity [START_REF] Tomimaru | Is Intraoperative Blood Loss Underestimated in Patients Undergoing Laparoscopic Hepatectomy?[END_REF]. The authors stated that due to a reduced workspace, blood suction might be less efficient in LLR compared with OLR, leading to an underestimation of intraoperative blood loss and highlighting the notion of "hidden blood loss". Of course, the importance of these results does not question the benefit of the laparoscopic approach since several significant limitations such as population heterogeneity, limited sample size, study reproducibility of the blood measurement, limit the strength of the message. However, it raises the question of reconsidering blood loss analysis during liver resection. Nevertheless, it should be kept in mind that impact of intraoperative blood loss on the postoperative outcomes is more relevant than the precise blood loss volume. In a recent series, an increased estimated blood loss >250 ml was associated with significantly higher overall complications and mortality after LLR [START_REF] Gupta | Impact of intraoperative blood loss on the short-term outcomes of laparoscopic liver resection[END_REF]. In other words, bleeding repercussions might therefore be best illustrated by blood transfusion requirement instead of intraoperative blood loss volume. Anyway, further trials focusing more specifically on blood loss measurements will provide additional data clarifying the benefit of laparoscopic approach on blood loss.

Moreover, several studies have demonstrated that patients might benefit from laparoscopic surgery with lower morbidity in many other abdominal surgeries [START_REF] Karakousis | Laparoscopic versus open gastric resections for primary gastrointestinal stromal tumors (GISTs): a size-matched comparison[END_REF][START_REF] Pham | Comparison of perioperative outcomes after combined thoracoscopiclaparoscopic esophagectomy and open Ivor-Lewis esophagectomy[END_REF]. After liver surgery, postoperative pulmonary complications are as common as cardiac complications and have yet been reported to greatly contribute to death and complication following surgery [START_REF] Nobili | Multivariate analysis of risk factors for pulmonary complications after hepatic resection[END_REF][START_REF] Cornell | Strategies to reduce postoperative pulmonary complications after noncardiothoracic surgery: systematic review for the American College of Physicians[END_REF]. Several factors are known to contribute to the occurrence of postoperative pulmonary complications in liver surgery. Of these a history of diabetes mellitus, a transverse subcostal bilateral muscle-cutting incision, a prolonged surgery, the presence of a nasogastric tube, and the need for intraoperative blood transfusion, are more strongly associated with their development [START_REF] Nobili | Multivariate analysis of risk factors for pulmonary complications after hepatic resection[END_REF]. Open major hepatectomies are mostly performed through bilateral subcostal or J-shaped incisions, with transection of the abdominal oblique and rectus muscles and prolonged retraction of the right hemi-diaphragm. On one hand, these large incisions may increase the risk of postoperative pulmonary complications through several mechanisms, including painful limitation of the rib cage excursion but also modification of diaphragmatic lymphatic drainage following dissection in the vicinity of the diaphragm and the diaphragmatic peritoneum. Open approach may result in a 50-60% reduction of the vital capacity and a 30% reduction in functional residual capacity [START_REF] Nobili | Multivariate analysis of risk factors for pulmonary complications after hepatic resection[END_REF]. On the other hand, although pneumoperitoneum increases pulmonary resistance, which can in turn result into intraoperative hypercapnia and negatively affect the postoperative pulmonary recovery [START_REF] Cornell | Strategies to reduce postoperative pulmonary complications after noncardiothoracic surgery: systematic review for the American College of Physicians[END_REF], the laparoscopic approach resulted in a dramatically decreased surgical wall trauma since only 5 or 6 port incisions are needed and the resected specimen is extracted through limited incisions including a suprapubic one without muscle section in 65% of the cases. In this context, decreased postoperative pain and early postoperative rehabilitation (49) may therefore provide improved pulmonary function recovery.

Finally, in addition to its clinical feasibility and safety, the cost-effectiveness of LLR was extensively debated, due to the expensive upfront payments for the disposable laparoscopy-related devices. Indeed, the benefit of LLR in term of cost-effectiveness may be attributed to the reduced postoperative morbidity rate, and shorter hospital stay [START_REF] Vanounou | Comparing the clinical and economic impact of laparoscopic versus open liver resection[END_REF]. In a US nationwide inpatient sample including 21280 patients who underwent liver resection from 2002 to 2012, the laparoscopic approach was consistently associated with improved postoperative outcomes including decreased postoperative morbidity (OLR vs. LLR: 32.9 vs. 29.6 %) and a shorter length of hospital stay (≤4 days; LLR, 21.4 %; OLR, 13.7 %; both p < 0.05) (50). Thus, it seems possible to hypothesize that LLR might provide economic benefit in patients with CRLM, based on a reduced morbidity and a shorter hospital stay.

SPECIFICITIES OF COLORECTAL LIVER METASTASES

Parenchymal sparing liver resection

Parenchymal sparing liver resection has been developed in open surgery to preserve hepatic function while achieving sufficient surgical margins. An increasing number of series have highlighted both technical and oncological benefits of parenchymal sparing hepatectomy in comparison with major hepatectomy [START_REF] Mise | Parenchymal-sparing Hepatectomy in Colorectal Liver Metastasis Improves Salvageability and Survival[END_REF][START_REF] Gold | Increased use of parenchymal-sparing surgery for bilateral liver metastases from colorectal cancer is associated with improved mortality without change in oncologic outcome: trends in treatment over time in 440 patients[END_REF]. However, laparoscopic approach was not popular in parenchymal sparing hepatectomy for deeply located tumors because it was more technically demanding since manipulations are limited [START_REF] Buell | World Consensus Conference on Laparoscopic Surgery. The international position on laparoscopic liver surgery: The Louisville Statement[END_REF][START_REF] Cipriani | Laparoscopic Parenchymal-Sparing Resections for Nonperipheral Liver Lesions, the Diamond Technique: Technical Aspects, Clinical Outcomes, and Oncologic Efficiency[END_REF]. In laparoscopic approach, parenchymal sparing hepatectomy for deeply located tumors in difficult-to-access areas can require intricate curved transection planes, technically more difficult than a single and straight transection plane during major hepatectomy [START_REF] Kawaguchi | Difficulty of Laparoscopic Liver Resection: Proposal for a New Classification[END_REF][START_REF] Hasegawa | Safely extending the indications of laparoscopic liver resection: When should we start laparoscopic major hepatectomy?[END_REF]. For these reasons, major hepatectomy resecting more non-tumorous parenchyma than required for tumor clearance, was often performed by laparoscopy. Recent technical advancement and better understanding of hepatic anatomy have enabled to perform laparoscopic parenchymal sparing hepatectomy even in difficult-to-access lesions ( 55) such as upper central [START_REF] Conrad | Laparoscopic parenchymal-sparing liver resection of lesions in the central segments: feasible, safe, and effective[END_REF] or posterosuperior segments [START_REF] Ogiso | Laparoscopic Transabdominal With Transdiaphragmatic Access Improves Resection of Difficult Posterosuperior Liver Lesions[END_REF], with a subsequent decrease of the rate of major hepatectomy. In these settings, surgeons should reconsider the importance of parenchymal sparing strategy and try to minimize the extent of resection even by laparoscopy.

Oncologic quality of the resection and long-term outcomes

Most series indicate that LLR allow similar oncological outcomes than OLR, such as tumor free surgical margins, 3-and 5-year disease-free and overall survival. Long-term outcome results of comparative series of laparoscopic versus open resections of CRLM are detailed in Table 1.

However, the positive results from LLR must be interpreted with caution due to the potential selection biases and small sample size, that may lead to inaccurate evaluation of outcomes and uncertain conclusions. The majority of relevant data were extracted merely from case series, casecontrol studies or meta-analyses of these studies [START_REF] Montalti | Laparoscopic liver resection compared to open approach in patients with colorectal liver metastases improves further resectability: oncological outcomes of a case-control matched-pairs analysis[END_REF][START_REF] Nachmany | Laparoscopic versus open liver resection for metastatic colorectal cancer[END_REF]. The sample size from each trial ranged from 36 to 450, that might explain the inconsistencies across different trials and have influenced the level of the evidence from these studies [START_REF] Cannon | Laparoscopic versus open resection of hepatic colorectal metastases[END_REF][START_REF] Beppu | Long-term and perioperative outcomes of laparoscopic versus open liver resection for colorectal liver metastases with propensity score matching: a multi-institutional Japanese study[END_REF][START_REF] Untereiner | Laparoscopic hepatectomy versus open hepatectomy for colorectal cancer liver metastases: comparative study with propensity score matching[END_REF][START_REF] Allard | Early and long-term oncological outcomes after laparoscopic resection for colorectal liver metastases: a propensity score-based analysis[END_REF][START_REF] Cipriani | Propensity score-based analysis of outcomes of laparoscopic versus open liver resection for colorectal metastases[END_REF][START_REF] Martínez-Cecilia | Laparoscopic versus open liver resection for colorectal metastases in elderly and octogenarian patients: a multicenter propensity score based analysis of short-and long-term outcomes[END_REF][START_REF] Ratti | Impact of totally laparoscopic combined management of colorectal cancer with synchronous hepatic metastases on severity of complications: a propensity-score-based analysis[END_REF][START_REF] Tranchart | Laparoscopic simultaneous resection of colorectal primary tumor and liver metastases: a propensity score matching analysis[END_REF]). Indeed, most of studies were completed between 1997 and 2016, and the huge advances in both chemotherapy and targeted therapies in the treatment of CRLM might explain the significant improvement of prognosis during this period. Therefore, the impact of the laparoscopic approach on the overall and disease-free survival after resection of CRLM is really difficult to identify. Also, the comparability of the patients included in these series is debated since the patients undergoing LLR of CRLM had smaller and more peripheral metastases than those treated with the open approach.

An interesting expected benefit of LLR in patients with CRLM would be its theoretical oncologic superiority. This could be achieved (i) provided that the oncologic quality of the resection (margins, rate of parenchymal sparing resection, quality of laparoscopic ultrasonography) is at least similar to that of OLR; and (ii) through a decrease of overall postoperative complications. Indeed, the longterm prognostic influence of major postoperative complications for different cancers (such as esophageal cancer) has previously been established and thus the observed improvement in survival from minimally invasive surgery, maybe mediated by the reduction in major complications.

In the specific setting of CRLM, decreasing postoperative complications yields two advantages: (a) a direct oncologic effect through a decrease in recurrence; (b) a higher feasibility of adjuvant chemotherapy including a shorter time to return to chemotherapy. The randomized study by Fretland et al. indicated that LLR was superior to open resection in reducing the inflammatory response [START_REF] Fretland | Inflammatory response after laparoscopic versus open resection of colorectal liver metastases: data from the Oslo-CoMet trial[END_REF]. This decreased inflammatory response is associated with better-preserved immune function during the postoperative period, which may lower the risk of surgical complications [START_REF] Veenhof | Surgical stress response and postoperative immune function after laparoscopy or open surgery with fast track or standard perioperative care: a randomized trial[END_REF].

Hence, the reduced inflammatory response achieved by laparoscopic approach might be one of the explanations for the decreased morbidity observed in the different series.

Interestingly, a recent study using a propensity score matching, found an approximately 2 weeks benefit for adjuvant chemotherapy administration after LLR. More importantly, in this series, all patients started adjuvant chemotherapy within 8 weeks after LLR, unlike OLR patients who had delayed adjuvant chemotherapy start in 34% of cases [START_REF] Kawai | Laparoscopic liver resection for colorectal liver metastasis patients allows patients to start adjuvant chemotherapy without delay: a propensity score analysis[END_REF]. The hypothesis is that, besides its potential impact on postoperative complications and the diminished surgical trauma, the minimally invasive approach may shorten postoperative recover, and thus help to start adjuvant chemotherapy within appropriate timing.

CRLM recurrence

Repeat hepatectomy for CRLM recurrence is increasingly performed owing to recent advances in the early diagnosis of recurrence, in chemotherapy efficiency, and in the expertise of hepatic surgery. In 2016 the group of the Institut Mutualiste Montsouris showed that laparoscopic repeat resection for recurrent CRLM was feasible and safe with acceptable perioperative mortality and morbidity after second and third LLR [START_REF] Nomi | Second and Third Laparoscopic Liver Resection for Patients With Recurrent Colorectal Liver Metastases[END_REF]. In addition, laparoscopic repeat hepatectomy provides an additional benefit of overall survival similar to that provided by first LLR. Even though laparoscopy significantly decreases adhesions formation, significant adhesions were observed in patients who had previous laparoscopic major hepatectomy or any other procedure in which the hepatic pedicle was dissected. A second or a third hepatectomy, even by laparoscopy, is technically more demanding and more time consuming due to technical difficulties from intra-abdominal adhesions, variations in liver anatomy on the hypertrophied remnant, chemotherapy induced liver injury but also higher intraoperative bleeding resulting in a higher risk of complications [START_REF] Andreou | Repeat hepatectomy for recurrent colorectal liver metastases is associated with a high survival rate[END_REF].

Bilobar disease and patient installation

In some situations, such as bilobar disease, laparoscopic resection of a posterior lesion associated with a lesion in left lobe for example can be difficult with a single installation of the patient. Indeed, for laparoscopic resection of lesions located in the posterior segment, the patient is placed in the left lateral decubitus position with the right arm suspended. In addition to 3 trocars placed in the right upper quadrant of the abdomen, 2 balloon-tipped trocars in order to isolate the chest from the abdominal cavity, one 5 mm and one 10 mm, can be disposed through the diaphragm in the same intercostal space. In this setting, the operative table should be rotated provided that reinforcement band prevent the patient fall. In some infrequent situations, the patient could be reinstalled during the surgical procedure in order to facilitate access to some « difficult segments ».

Laparoscopic ultrasonography

Ultrasound exploration of the liver during laparoscopic resection of CRLM is more challenging than in open approach especially when both posterior and anterior lesions need to be resected.

Laparoscopic ultrasonography has been proven to be an indispensable tool in all laparoscopic liver procedures [START_REF] Zhu | Intraoperative ultrasonography of robot-assisted laparoscopic hepatectomy: initial experiences from 110 consecutive cases[END_REF][START_REF] Garancini | Intraoperative ultrasound: a review on its role in liver surgery for primitive and metastatic tumors[END_REF][START_REF] Tang | Augmented reality technology for preoperative planning and intraoperative navigation during hepatobiliary surgery: A review of current methods[END_REF]. The laparoscopic ultrasonography allows all intraoperative procedures such as resection, biopsy, or radiofrequency ablation. The major disadvantage of laparoscopic ultrasonography is that the image orientation is difficult to interpret. The images are small, specular, and present with shadowing and reflection artifacts with a variable contrast. Therefore, the quality of the image is operator-dependent, which represents another disadvantage. Nevertheless, the realtime imaging capabilities and the convenience of laparoscopic ultrasonography for intraoperative use compensate many of the disadvantages. Indeed, development of navigation technology or the use of contrast agents during laparoscopic procedures guided by laparoscopic ultrasonography would solve the orientation problems in the future.

FUTURE ADVANCES

Augmented reality guidance systems

Despite its proven benefits and the adaption of modern technology to reduce the learning curve, minimally invasive liver surgery is presently used only in specialized centers. Surgeons still struggle with the anatomy and identification of major vascular and nonvascular structures within the liver parenchyma. Although preoperative CT and intraoperative ultrasonography are useful to surgeons, these imaging systems are either not in real-time or they show only a small part of the entire picture. As a result, many researchers are working on developing a real-time anatomical map of a patient's liver to assist surgeons navigate challenging dissections. Augmented reality guidance systems have been used for real-time image guidance. Surgeons can obtain intraoperative fluoroscopic C-arm con-beam CT (CBCT) images. Software can be used to produce a real-time overlay of these images to highlight important structures during dissection. Ideally, if augmented reality guidance systems can provide real anatomical information during surgery, it can help orient surgeons, which would lead to fewer intraoperative complications [START_REF] Kenngott | Real-time image guidance in laparoscopic liver surgery: first clinical experience with a guidance system based on intraoperative CT imaging[END_REF].

ICG is a widely available dye that absorbs and emits light in the near-infrared (NIR) spectrum.

Advances in imaging technologies have led to the development of NIR cameras to visualize injected dye in humans. Because ICG is hepatically cleared, it has become clinically important in liver surgery because it can identify intrahepatic lesions even when preoperative CT, palpation, inspection, and intraoperative ultrasound cannot [START_REF] Lim | Indocyanine green fluorescence imaging in the surgical management of liver cancers: current facts and future implications[END_REF]. Well-differentiated tumors absorb ICG, therefore result in homogenous fluorescence. Poorly differentiated and metastatic tumors do not absorb or excrete dye therefore develop a rim of ICG or halo sign [START_REF] Ishizawa | Mechanistic background and clinical applications of indocyanine green fluorescence imaging of hepatocellular carcinoma[END_REF]. In a study published in 2014, 276 hepatocellular carcinomas were resected, including 273 identified by ICG (99% success rate) [START_REF] Van Der Vorst | Near-infrared fluorescence-guided resection of colorectal liver metastases[END_REF]. In a series of 40 patients with CRLM, intraoperative ICG discovered unanticipated LM in 5 (12,5%) [START_REF] Van Der Vorst | Near-infrared fluorescence-guided resection of colorectal liver metastases[END_REF]. ICG can even be used to distinguish benign from malignant lesions [START_REF] Lim | Indocyanine green fluorescence imaging in the surgical management of liver cancers: current facts and future implications[END_REF]. Use of this dye has been used to increase identification of lesions and is being more frequently employed for both open and minimally invasive approaches.

3D Visualization

Three-dimensional (3D) visualization gives better depth perception than the tradition twodimensional (2D) screens used in laparoscopy. This enhanced depth perception is excellent to enable accurate dissection and identification of intraparenchymal vessels. A study by Velayutham et al. compared major liver resection using 3D and 2D laparoscopy. No difference was seen in blood loss or major complications; however, the operative time was significantly shortened in the 3D group [START_REF] Velayutham | 3D visualization reduces operating time when compared to high-definition 2D in laparoscopic liver resection: a case-matched study[END_REF].

Robotic Instruments

Ergonomics is still a problem for complex laparoscopic surgery. There is a limited number of degrees of freedom (DOF) of laparoscopic instruments due to the passage of the shaft through the trocar as well as the fixed position of the trocar on the abdominal wall. These factors limit laparoscopic instruments to four DOF compared to a human arm which has nine DOF. As a result, this limits the surgeon's freedoms of movement including during the most basic surgical maneuvers like tying intracorporeal knots. As a result, most of laparoscopic surgeons suffer from musculoskeletal pain often in the upper back and neck due to awkward positioning while performing surgery [START_REF] Wauben | Application of ergonomic guidelines during minimally invasive surgery: a questionnaire survey of 284 surgeons[END_REF]. To overcome these two issues, researchers are developing robotized laparoscopic instruments, to improve surgeon postures and add more DOF thus facilitating the most difficult surgical maneuvers [START_REF] Zahraee | Towards the development of a hand-help surgical robot for laparoscopy[END_REF][START_REF] Herman | Ergonomic and gesture performance of robotized instruments for laparoscopic surgery[END_REF]. In addition, these instruments allow the surgeon to still receive haptic feedback, that telemanipulated surgical devices like the da Vinci® robot cannot provide [START_REF] Bensignor | Evaluation of the effect of a laparoscopic robotized needle holder on ergonomics and skills[END_REF]. These new robotized instruments appear to be the future of laparoscopic surgery since they improve ergonomics and surgical skill, and could increase the overall quality of the surgical procedure.

CONCLUSION

Although laparoscopic surgery for primary colorectal cancer is well documented and widely used, laparoscopic surgery for CRLM has developed more slowly. The presumed obstacles to this approach included foremost a long-lasting learning curve, fear of difficult-to-control bleeding or gas embolism, and issues regarding patient selection. However, in spite of these difficulties, laparoscopic approach showed strong advantages in early postoperative course, and offered similar oncological outcomes compared with open approach. A large pragmatic randomized study with less selection of the patients could reinforce its diffusion in the field surgery of CRLM.

Highlights:

1. The main obstacles to laparoscopic liver resection (LLR) for colo-rectal metastases (CRLM) are the risk of gas embolism, the difficulties to locate intraparenchymal lesions and to achieve hemostasis.

2.

LLR is associated with reduced blood loss, lower morbidity rates, shorter length of hospital stay and earlier return to functional activities.

3.

Other advantages of LLR could include less tissue damage, less surgical stress, and reduced overall costs.

4.

Oncological outcomes of LLR for CRLM such as rates of R0 margin and tumor recurrence, and 5year overall survival offered by the laparoscopic approach seem similar to that obtained after open approach.

5. However, the level of scientific evidence of comparative studies between open and laparoscopic approaches remains low, suggesting the need for further studies, including randomized control trials.

Table 1 .

 1 Results of comparative series of laparoscopic resection of cancer colorectal liver metastases: short-and long-term outcomes

Author