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O'Keefe, Richard --- "Causation problems in medical negligence cases" [2023] PrecedentAULA 17; (2023) 175 Precedent 18

CAUSATION PROBLEMS IN MEDICAL NEGLIGENCE CASES

By Richard O’Keefe

In medical negligence cases, causation is often the most difficult element to establish in a claim. Some of the pertinent issues that commonly arise in such cases with respect to factual causation are described in this article.

Establishing factual causation is usually the more difficult element of establishing legal causation of the particular harm of which the plaintiff complains. Given the test for causation is clearly established as the ‘but for’ test, the question then arises as to what evidentiary onus is required to fulfil the ‘but for’ test and establish causation.

It is important to distinguish between the legal onus, which the plaintiff bears, and the evidence that is sufficient to satisfy that onus. The law imposes an evidentiary onus on the plaintiff in establishing causation, as noted by Basten JA in Elbourne v Gibbs:^[1]

‘Where it is demonstrated that a defendant has breached a duty owed to a plaintiff, and harm has followed, it would be understandable that the law might impose an onus on the defendant to show that his or her breach of duty had not caused the harm. However, that course has not been taken and it is clear beyond doubt that the burden of establishing causation lies on the plaintiff.’

Evidence must be sufficient in a civil case to satisfy the balance of probability legal test.^[2] In practice this means that the trial judge and appellate court must be persuaded that the contended for facts/events happened.

In Tabet v Gett,^[3] Kiefel J observed:

‘The general standard of proof required by the common law and applied to causation is relatively low. It does not require certainty or precision. It requires that a judge be persuaded that something was probably a cause of the harm the plaintiff suffered. Historically the standard may have been chosen in order to minimise errors in civil jury trials, but it nevertheless serves also to accommodate a level of uncertainty in proof.’

Principles to consider

A helpful summary of the principles to consider with respect to proof was provided by McDougall J in Nguyen v Cosmopolitan Homes (NSW) Pty Ltd:^[4]

‘1. A finding that a fact exists (or existed) requires that the evidence induce, in the mind of the fact-finder, an actual persuasion that the fact does (or at the relevant time did) exist;

2. Where on the whole of the evidence such a feeling of actual persuasion is induced, so that the fact-finder finds that the probabilities of the fact’s existence are greater than the possibilities of its non-existence, the burden of proof on the balance of probabilities may be satisfied;

3. Where circumstantial evidence is relied upon, it is not in general necessary that all reasonable hypotheses consistent with the non-existence of a fact, or inconsistent with its existence, be excluded before the fact can be found; and

4. A rational choice between competing hypotheses, informed by a sense of actual persuasion in favour of the choice made, will support a finding, on the balance of probabilities, as to the existence of the fact in issue.’

Causation is a retrospective factual inquiry by the court – Vairy v Wyong Shire Council^[5] – and the fact-finding process prefers past events, known facts, to prophecy: Johnson v Perez.^[6] For example, if a plaintiff sustains injury from using a particular drug, and information regarding the toxicity of the drug is discovered only after the injury, that evidence will be admissible for proving causation.

Proof of causation will depend upon the admission into evidence of facts from which the cause of an event can either be observed or inferred. In medical negligence cases difficulties often arise in the context of proof of causation. There are numerous reasons for this, ranging from the inability to observe cause and effect by direct observation (such as the metastases of a cancer) to the lack of established scientific knowledge in novel situations (such as the side effects of exposure to a new drug).

Consequently, when investigating a potential medical negligence claim, it is often preferable for the sake of economy to focus attention first on the issue of causation before investigating and incurring costs obtaining expert opinion to establish breach of duty of care.

When problems arise

Problems arise when unanimous professional peer opinion cannot directly affirm causation. A number of difficult scenarios commonly arise when it comes to fulfilling the evidentiary onus that exists as part of the ‘but for’ test:

1. Problems with evidence:

1.1. No evidence to establish that an event did or would have occurred or not occurred.

1.2. Insufficient evidence to establish that an event did or would have occurred or not occurred.

1.3. Conflicting evidence to establish that an event did or would have occurred or not occurred.

2. Multiple events:

2.1. Concurrent causes and conditions produce the damage.

2.2. Successive acts or omissions produce the damage.

The most conclusive fulfillment of the ‘but for’ test in medical negligence cases is where peer professional opinion clearly attests to direct causation. However, a finding of causal connection may be open, absent supportive expert evidence, or even where the expert evidence proves no more than that a causal connection is possible. The evidence will be sufficient if, but only if, the evidence justifies an inference of probable, as opposed to possible, connection.

In Naxakis v Western General Hospital (Naxakis)^[7] Gaudron J said:

‘For the purposes of the allocation of legal responsibility, “[i]f a wrongful act or omission results in an increased risk of injury to the plaintiff and that risk eventuates, the defendant's conduct has materially contributed to the injury that the plaintiff suffers whether or not other factors also contributed to that injury occurring”. And in that situation, the trier of fact – in this case, a jury – is entitled to conclude that the act or omission caused the injury in question unless the defendant establishes that the conduct had no effect at all or that the risk would have eventuated and resulted in the damage in question in any event’ [footnotes omitted].

A jury direction in accordance with the judgment of McHugh J in Chappel v Hart (Chappel)^[8] in similar terms to the above passage was approved in Freidin v St Laurent (Freidin).^[9] That case involved an allegation that a negligent failure to perform an episiotomy caused severe perineal injuries. The decision in Freidin was referred to with approval in Queen Elizabeth Hospital v Curtis,^[10] where a hospital was found to have negligently failed to make a timely diagnosis of meningitis, thus delaying commencement of treatment resulting in brain damage that would otherwise have been reduced.

In Naxakis, Gaudron J also said that:

‘For the purpose of assigning legal responsibility ... a common sense approach which allows that “breach of duty coupled with an [event] of the kind that might thereby be caused is enough to justify an inference, in the absence of any sufficient reason to the contrary, that in fact the [event] did occur owing to the act or omission amounting to the breach”’.^[11]

The principle that causation can be established by proof of a breach of duty coupled with an injury, which it is known can be caused by such a breach, is however controversial. Where the question for decision is whether, on the balance of probabilities, event A caused the result B, the burden of proof is not satisfied merely by evidence that it is possible that the causal relationship exists. See the decision of Spigelman CJ in Seltsam Pty Ltd v McGuiness (Seltsam).^[12] However, as their Honours pointed out in Seltsam,^[13] the inference of causation may be drawn from all of the evidence in the case, including expert evidence as to the possibility that the causal relationship exists.

A significant increase in statistical risk of harm has been recognised to be sufficient for causation in some cases. In Sydney Southwest Area Health Service v Stamoulis^[14] there was evidence that a 10-month delay in detecting breast cancer meant that the chance of metastasis increased from 38 per cent to 42 per cent. This amounted to a 10 per cent increase in the risk of metastasis which had in fact occurred. Ultimately, the Court of Appeal found that the risk had been increased to an extent that was not negligible and applied the ‘common-sense’ test on causation; see also EMI (Aust) Ltd v Bes;^[15] Elbourne v Gibbs;^[16] Pierce v Metro North Hospital and Health Service;^[17] and East Metropolitan Health Service v Ellis (Ellis).^[18]

If there is general information, such as data derived from medical trials or other studies or learning, it is always necessary to adduce some evidence that the general data or statistical correlations can be applied to the circumstances of the particular case. In Amaca v Booth,^[19] French CJ held that the mere existence of a statistical correlation between two events does not necessarily imply a causal relationship. However, if a causal explanation for the correlation can be found, it may be possible to conclude that the first event was a contributing cause of the second event, using the standard of proof of balance of probabilities. The strength of the association between the two events may also support an inference of a causal connection.

The West Australian Supreme Court of Appeal provided the most recent summary of relevant principles in Ellis, which built upon the exposition of principles by the NSW Court of Appeal and the High Court. In Ellis, the Court noted that causation may be established through inference, and if direct proof is not available, an inference of causation may be drawn if the relevant circumstantial evidence is ‘sufficiently strong and coherent’.^[20] When it comes to expert opinion admitted into evidence, the Court held that if it is presented, the Court must take it into account and accord such weight as is appropriate. However, plaintiffs are not always required to provide expert evidence to prove causation and judges are not required to find causation based solely on expert testimony. It is possible for a court to infer causation even if the expert witnesses do not affirmatively say that the damage was caused by the breach in question. Causation can be inferred even without medical evidence or if the expert evidence only indicates that a causal connection is possible. A court can draw this inference as long as the available evidence as a whole supports the probable connection.

In Ellis the Court provided guidance on the circumstance where an expert witness may be unable to help: If the cause of an event is unclear or a subject of scientific debate, a court is still capable of making decisions about causation based on the balance of probabilities. In these cases, evidence of the possibility of causation, such as epidemiological studies, can be considered circumstantial evidence that may help establish causation in a specific instance. As with any circumstantial evidence, an inference about the likelihood of causation can be made based on several pieces of evidence, even if each individual piece does not provide conclusive proof on its own. In other words, a combination of proven facts which attest to the possibility of an event causing another event may be sufficient to establish causation of harm.

The Court likened the process of finding a causal relationship to combining strands in a cable, contrasting it with that of links in a chain. The Court found that causation doesn’t require an intermediate fact to be established, merely the ultimate inference.

Key pointers

From the Court’s restatement of relevant principles in Ellis, one can derive a few key pointers for practitioners when considering if causation can be made out in a particular case:

1. Causation may be inferred through circumstantial evidence.

2. Expert evidence is not necessarily required for courts to find a causal relationship.

3. If expert evidence is provided, it does not necessarily have to attest to a direct causal relationship, merely the possibility of one, as long as on the whole, the evidence supports the existence of a causal relationship.

4. In circumstances where the medical science is undecided, the court may accept tentative evidence of the possibility of a causal relationship, such as epidemiological studies.

A useful example of this approach to causation is to be found in Dhupar v Lee,^[21] in which the plaintiff was able to establish that the Filshie clip that detached from her fallopian tube and led to an unwanted pregnancy was due to negligent application, by the plaintiff’s use of a matrix of evidence, including:

• evidence from the defendant regarding the manner in which the procedure was performed;

• intraoperative photographic evidence of tissues;

• direct observations of anatomic structures made by a treating doctor at the subsequent delivery of the child;

• medical literature that suggested a link between defective technique and clip failure if a pregnancy occurred within 12 months of the Filshie clip sterilisation procedure; and

• data regarding the generally accepted high success rate of the procedure.

In cases where there may be multiple, concurrent or successive causes of harm, practitioners should bear in mind that it is not necessary for a plaintiff to establish the mechanism of the cause of the loss with precision. The factual causation of loss by the breach of duty of a defendant is to be assessed on the balance of probabilities, including in circumstances in which alternative causes are possible: Circular Head Fencing Pty Ltd v Motor Accidents Insurance Board.^[22]

When a hypothetical and different state of affairs is contended for in order to establish factual causation, a plaintiff must adduce evidence about what would have occurred but for the defendant’s negligence. Section 5D(3)(a) of the Civil Liability Act 2002 (NSW) (CLA)^[23] provides that if it is relevant to the determination of factual causation to determine what the person who suffered harm would have done if the negligent person had not been negligent the matter is to be determined subjectively in the light of all relevant circumstances.

The plaintiff, however, cannot give evidence about what he or she would have done except to the extent (if any) that the statement is against his or her interest: s5D(3)(b), CLA.

The adoption of a subjective test is consistent with common law decisions which have held that one must consider what the particular plaintiff, as opposed to a reasonable person in her position, would have done had she been given the advice she should have been given: Chappel.^[24]

In Varipatis v Almario (Varipatis)^[25] the plaintiff suffered from terminal liver cancer and alleged that the defendant (a general practitioner) was legally responsible for failing to procure appropriate treatment over a lengthy period to enable him to lose weight including bariatric surgery. Had that occurred, the plaintiff would have lost weight and cirrhosis and consequent cancer would not have developed. The trial judge accepted this argument.

The Court of Appeal upheld an appeal, holding that the general practitioner’s duty was to advise the patient that weight loss was necessary, to discuss ways that could be achieved and to offer and encourage acceptance of referrals, but no more than that. Justice of Appeal Meagher noted:

‘[A] finding of negligence constituted by an omission to act or advise requires consideration of the probable course of events had, in this case, the appellant not been negligent in the respects found: Strong v Woolworths Ltd [2012] HCA 5; 86 ALJR 267 at [18]. This made it necessary to consider what was likely to have happened if the appellant by 30 July 1998, either had referred Mr Almario to a bariatric surgeon or taken active steps to refer him to an obesity clinic.’^[26]

In cases such as Varipatis and failure to warn claims, it is vital to the plaintiff’s success to establish by evidence emanating from sources other than the plaintiff that but for the defendant’s breach of duty the plaintiff would have acted in a particular way to have avoided the particular harm suffered. Helpful evidence may also include evidence of statistics concerning the number of persons who decline to proceed with a specific treatment when warned of various risks and evidence of the plaintiff’s reluctance to undergo other medical procedures prior to the impugned event. A thorough examination of pre-incident medical history and life events must be undertaken to identify whether such information exists and can be tendered in evidence.

Policy considerations that are relevant to normative causation (application of s5D(4), CLA) must always be borne in mind, particularly in relation to failure to warn claims and cases where the alleged breach of duty is novel or controversial. In such cases there must be a direct relationship between the subject matter requiring a warning and the scope of liability for harm.

In Wallace, the High Court rejected an appeal by a plaintiff who established breach of duty but failed on causation. He underwent spinal surgery. One risk of the procedure was temporary nerve damage resulting from immobility during the procedure. Another risk was catastrophic paralysis from direct nerve damage. The plaintiff claimed he was not advised of either risk. The less serious risk, neuropraxia, eventuated. The plaintiff sued the defendant and claimed that if he was warned pre-operatively of the more serious risk of permanent paralysis then he would not have proceeded with the operation. The trial judge found that even though the plaintiff had not been warned of the neuropraxia, he would have chosen to undergo the surgical procedure even if he had been warned of that risk. The causative link was not established as it was not within the scope of liability under section 5D(1)(b) of the CLA. The plaintiff also failed in the Court of Appeal. The High Court held that in order to establish causation between the failure to warn and injury, that injury must have been caused by the particular failure to warn. It is not necessarily appropriate for the doctor to be liable for materialisation of a risk about which he had a duty to warn, even if factual causation is established.

The High Court held that it was necessary to look at the policy underlying the imposition of the duty. The policy here was not to protect the patient from exposure to all unacceptable risks, rather it was to protect the patient from an unacceptable risk of physical injury.

Richard O’Keefe is a member of Maurice Byers Chambers in Sydney and practises in all Australian jurisdictions in personal injury litigation with a special interest in medical negligence law. Richard was recognised by Doyle’s Guide as pre-eminent junior counsel – personal injury and insurance law in 2022, 2021 and 2020 and recommended professional indemnity junior counsel in 2021. Richard is a co-editor of Professional Liability in Australia (4th ed, Lawbook Co, 2023), responsible for the chapter ‘Doctors’.

^[1] [2006] NSWCA 127, [75].

^[2] Section 140, Evidence Act 1995 (NSW).

^[3] [2010] HCA 12, [145].

^[4] [2008] NSWCA 246, [55].

^[5] [2005] HCA 62; 223 CLR 422, [124].

^[6] [1988] HCA 64; 166 CLR 351, [6].

^[7] [1999] HCA 22; 197 CLR 269, [31] (Naxakis).

^[8] [1998] HCA 55; 195 CLR 232, [34] (Chappel).

^[9] [2007] VSCA 16; (2007) 17 VR 439, [19]–[20] (Chernov JA) (Freidin).

^[10] [2008] SASC 344; (2008) 102 SASR 534, [49].

^[11] Naxakis, above note 7, [36], citing Betts v Whittingslowe [1945] HCA 31; (1945) 71 CLR 637, 649 (Dixon J).

^[12] [2000] NSWCA 29; (2002) 49 NSWLR 262, 275 [80].