Snell v. Farrell, [1990] 2 S.C.R. 311

Dr. D. H. Farrell Appellant

v.

Margaret Snell Respondent

indexed as: snell v. farrell

File No.: 20873.

1989: December 6; 1990: August 16.

Present: Dickson C.J.* and Wilson, La Forest, L'Heureux‑Dubé, Sopinka, Cory and McLachlin JJ.

on appeal from the court of appeal for new brunswick

Physicians and surgeons ‑‑ Medical malpractice ‑‑ Negligence ‑‑ Causation ‑‑ Surgeon removing cataract from patient's eye ‑‑ Patient later losing sight in that eye as a result of optic nerve atrophy ‑‑ Expert witnesses unable to state with certainty whether the operation caused the atrophy ‑‑ Whether burden of proof of causation in a malpractice case is on the plaintiff.

Negligence ‑‑ Causation ‑‑ Medical malpractice ‑‑ Burden of proof ‑‑ Surgeon removing cataract from patient's eye ‑‑ Patient later losing sight in that eye as a result of optic nerve atrophy ‑‑ Expert witnesses unable to state with certainty whether the operation caused the atrophy ‑‑ Whether burden of proof of causation in a malpractice case is on the plaintiff.

The appellant, an ophthalmologist, performed surgery on the respondent to remove a cataract from her right eye. After injecting a local anaesthetic into the retrobulbar muscles behind the eyeball, the appellant noticed a small discolouration, which he stated on discovery was a very small retrobulbar bleed. On palpitating the eye, he found that it was not hard, and there were no other signs of retrobulbar haemorrhage. After waiting thirty minutes he proceeded with the operation. Following the surgery there was blood in the vitreous chamber of the eye. When the chamber cleared some nine months later the appellant was able to see for the first time that the optic nerve had atrophied, resulting in a loss of sight in the respondent's right eye. One possible cause of optic nerve atrophy is pressure due to retrobulbar haemorrhage. Neither of the expert witnesses was able to state with certainty what caused the atrophy in this case or when it occurred. The trial judge accepted the expert evidence that where there is bleeding other than the obvious pinprick of the needle, the operation should not be continued. Relying on the decision of the House of Lords in McGhee v. National Coal Board, he concluded that the respondent had prima facie proved that the appellant's actions had caused her injury and that the appellant had not satisfied the onus that had shifted to him. The trial judge accordingly found the appellant liable in negligence. The Court of Appeal dismissed the appellant's appeal.

Held: The appeal should be dismissed.

While proof of causation in medical malpractice cases is often difficult for the patient, it is unnecessary to adopt either of the alternatives arising out of the McGhee case ‑‑ namely, that the plaintiff simply prove that the defendant created a risk that the injury which occurred would occur, or that the defendant has the burden of disproving causation ‑‑ since, properly applied, the traditional principles relating to causation are adequate to the task. Adoption of either of the proposed alternatives would have the effect of compensating plaintiffs where a substantial connection between the injury and the defendant's conduct is absent. A plaintiff should not be compensated by reversing the burden of proof for an injury that may very well be due to factors unconnected to the defendant and not the fault of anyone.

Dissatisfaction with the traditional approach to causation stems to a large extent from its too rigid application in many cases. Causation need not be determined with scientific precision. In many malpractice cases, the facts lie particularly within the knowledge of the defendant, and very little affirmative evidence on the part of the plaintiff will justify the drawing of an inference of causation in the absence of evidence to the contrary. It is not strictly accurate to speak of the burden of proof shifting to the defendant when what is meant is that evidence adduced by the plaintiff may result in an inference being drawn adverse to the defendant. The legal or ultimate burden remains with the plaintiff, but in the absence of evidence to the contrary adduced by the defendant an inference of causation may be drawn although positive or scientific proof of causation has not been adduced. If some evidence to the contrary is adduced by the defendant, the trial judge should weigh that evidence according to the proof. It is therefore not essential that the medical experts provide a firm opinion supporting the plaintiff's theory of causation. Medical experts ordinarily determine causation in terms of certainties whereas a lesser standard is demanded by the law. It is the function of the trier of fact, not the medical witnesses, to make a legal determination of the question of causation.

In this case, the appellant was negligent in continuing with the operation when retrobulbar bleeding occurred. This finding was not contested and was fully supported by the evidence. It was common ground that the respondent's blindness occurred due to atrophy or death of the optic nerve which was occasioned by a stroke. There were two possible causes of the stroke, one of which was natural and the other due to continuing the operation. The trial judge virtually ruled out natural causes when he found that retrobulbar bleeding was facilitated during the operation. The trial judge's subsequent finding that the respondent had prima facie proved that the appellant's actions caused her injury and that the appellant had not satisfied the onus shifted to him can be read as a finding of causation inferred from the circumstances. While such a reading was probably not intended by the trial judge, had he applied the proper principles of law, he would have drawn an inference of causation between the appellant's negligence and the injury to the respondent. By continuing the operation, which was found by the trial judge to constitute negligence, the appellant made it impossible for the respondent or anyone else to detect the bleeding which is alleged to have caused the injury. In these circumstances, it was open to the trial judge to draw the inference that the injury was caused by the retrobulbar bleeding. The fact that testing the eye for hardness did not disclose bleeding is insufficient to rebut this inference.

Cases Cited

Not followed: McGhee v. National Coal Board, [1973] 1 W.L.R. 1; considered: Wilsher v. Essex Area Health Authority, [1988] 2 W.L.R. 557, rev'g [1987] 2 W.L.R. 425; referred to: Finlay v. Auld, 1973 CanLII 188 (SCC), [1975] 1 S.C.R. 338; Sindell v. Abbott Laboratories, 607 P.2d 924 (1980); National Trust Co. v. Wong Aviation Ltd., 1969 CanLII 11 (SCC), [1969] S.C.R. 481; Cook v. Lewis, 1951 CanLII 26 (SCC), [1951] S.C.R. 830; Summers v. Tice (1948), 5 A.L.R. (2d) 91; Interlake Tissue Mills Co. v. Salmon and Beckett, 1948 CanLII 74 (ON CA), [1949] 1 D.L.R. 207; Cudney v. Clements Motor Sales Ltd., 1969 CanLII 200 (ON CA), [1969] 2 O.R. 209; Kirk v. McLaughlin Coal & Supplies Ltd., 1967 CanLII 345 (ON CA), [1968] 1 O.R. 311; Jackson v. Millar (1972), 1972 CanLII 44 (ON CA), 31 D.L.R. (3d) 263; Powell v. Guttman (1978), 1978 CanLII 1933 (MB CA), 89 D.L.R. (3d) 180; Letnick v. Toronto (Municipality of Metropolitan), 1988 CanLII 9438 (FCA), [1988] 2 F.C. 399; Dalpe v. City of Edmundston (1979), 1979 CanLII 3239 (NB CA), 25 N.B.R. (2d) 102; Nowsco Well Service Ltd. v. Canadian Propane Gas & Oil Ltd. (1981), 1981 CanLII 2034 (SK CA), 122 D.L.R. (3d) 228; Rendall v. Ewert (1989), 1989 CanLII 232 (BC CA), 38 B.C.L.R. (2d) 1; Kitchen v. McMullen (1989), 1989 CanLII 218 (NB CA), 100 N.B.R. (2d) 91; Westco Storage Ltd. v. Inter‑City Gas Utilities Ltd., 1989 CanLII 7270 (MB CA), [1989] 4 W.W.R. 289; Haag v. Marshall, 1989 CanLII 236 (BC CA), [1990] 1 W.W.R. 361; Alphacell Ltd. v. Woodward, [1972] 2 All E.R. 475; Blatch v. Archer (1774), 1 Cowp. 63, 98 E.R. 969; Cummings v. City of Vancouver (1911), 1911 CanLII 265 (BC CA), 1 W.W.R. 31; Dunlop Holdings Ltd.'s Application, [1979] R.P.C. 523; Diamond v. British Columbia Thoroughbred Breeders' Society (1965), 1965 CanLII 474 (BC SC), 52 D.L.R. (2d) 146; Pleet v. Canadian Northern Quebec R. Co. (1921), 1921 CanLII 518 (ON CA), 64 D.L.R. 316; Guaranty Trust Co. of Canada v. Mall Medical Group, 1969 CanLII 78 (SCC), [1969] S.C.R. 541; Sentilles v. Inter‑Caribbean Shipping Corp., 361 U.S. 107 (1959).

Authors Cited

Cross, Sir Rupert. Cross on Evidence, 6th ed. By Sir Rupert Cross and Colin Tapper. London: Butterworths, 1985.

Fleming, John G. "Probabilistic Causation in Tort Law" (1989), 68 Can. Bar Rev. 661.

Great Britain. Royal Commission on Civil Liability and Compensation for Personal Injury. Report, vol. I. London: H. M. Stationery Off., 1978.

Harvey, David M. Medical Malpractice. Indianapolis: A. Smith, 1973.

Louisell, David W. Medical Malpractice, vol. 3. By Charles Kramer. New York: Matthew Bender, 1977‑1990.

Posner, James R. "Trends in Medical Malpractice Insurance, 1970‑1985", 49 Law & Contemp. Probs., Spring 1986, p. 37.

Robinson, Glen O. "The Medical Malpractice Crisis of the 1970's: A Retrospective", 49 Law & Contemp. Probs., Spring 1986, p. 5.

Wigmore, John Henry. Evidence in Trials at Common Law, vol. 9. Revised by James H. Chadbourne. Boston: Little, Brown & Co., 1981.

APPEAL from a judgment of the New Brunswick Court of Appeal, (1988), 1988 CanLII 8128 (NB CA), 84 N.B.R. (2d) 401, 214 A.P.R. 401, affirming the judgment of the Court of Queen's Bench (1986), 1986 CanLII 5365 (NB QB), 77 N.B.R. (2d) 222, 195 A.P.R. 222, 40 C.C.L.T. 298, finding the appellant liable in negligence for the respondent's loss of vision in her right eye. Appeal dismissed.

B. A. Crane, Q.C., and Margaret Ross, for the appellant.

E. Neil McKelvey, Q.C., and Kenneth B. McCullogh, for the respondent.

//Sopinka J.//

The judgment of the Court was delivered by

SOPINKA J. -- The issue of law in this case is whether the plaintiff in a malpractice suit must prove causation in accordance with traditional principles or whether recent developments in the law justify a finding of liability on the basis of some less onerous standard. The practical effect of a determination of this issue will be whether the appellant was liable for the loss by the respondent of the vision in her right eye.

The Facts

The respondent, age 70 at the time of trial, consulted the appellant with respect to problems with her vision. The appellant is a medical doctor specializing in the field of ophthalmology. The respondent was "legally blind" in her right eye. She was advised that she had a cataract which should be surgically removed. After the appellant had explained the operation and the risks involved, the respondent consented. The accepted procedure for elderly patients consisted of local anaesthetization, to avoid risks associated with general anaesthetic, followed by removal of the cataract and implantation of a prosthetic lens into the anterior chamber of the eye behind the cornea.

The procedure is first to anaesthetize the eyelid to prevent blinking. Then a needle is inserted underneath the eyeball to inject anaesthetic into the retrobulbar muscles behind the eyeball to prevent movement and pain. These muscles control eye movement and surround the optic nerve. One complication, which occurs in one to three percent of cases, is haemorrhage in the retrobulbar area caused by inserting the needle. There is no treatment for such haemorrhage but to let it be reabsorbed naturally. A common result of such haemorrhage is pressure behind the eyeball, which can cause the contents of the eye to be expelled when an incision is made in the cornea during the procedure to remove the cataract. Both experts testifying at trial stated that if retrobulbar haemorrhage occurs, the operation should not be continued. They also testified that an incision into the eye would remove the tamponade effect created by an intact eyeball, allowing a retrobulbar haemorrhage to flow more freely.

The classic symptoms of retrobulbar haemorrhage are redness of the eyelids where they touch the eyeball, and hardness of the eye. After injecting the anaesthetic into the retrobulbar area of the eye, Dr. Farrell noticed a small discolouration, one to two centimeters in diameter, at the puncture site below the eye on the surface of the skin. On discovery he stated that this was a very small retrobulbar bleed. He palpitated the eye, finding that it was not hard, and there were no other signs of retrobulbar haemorrhage. After waiting thirty minutes he proceeded with the surgery. The operation went normally. The trial judge accepted Mrs. Snell's evidence that Dr. Farrell told another doctor assisting him that he would have to hurry the operation.

Following the surgery Mrs. Snell developed excruciating pain and was given pain killers. That evening Dr. Farrell removed the patch on Mrs. Snell's eye, finding more blood than at the time of surgery. A retrobulbar bleed had obviously occurred. Dr. Farrell found there to be pressure on the eye, although it was not too great and he did not accurately measure it until a month later. There was blood in the anterior chamber, which cleared rapidly, and blood in the vitreous chamber, which took some nine months to clear. When the vitreous chamber cleared Dr. Farrell was able to see for the first time that the optic nerve had atrophied, resulting in the loss of sight in Mrs. Snell's right eye.

Atrophy results from a loss of the optic nerve's blood supply. One possible cause is pressure due to retrobulbar haemorrhage. The plaintiff's expert, Dr. Samis, examined Mrs. Snell in 1985 (about 17 months after the operation) finding new blood vessel formation in the iris, which indicated that she had suffered a stroke in the back of the eye at some point. He could not identify what caused the stroke. He testified that a major cause of optic nerve atrophy is a stroke in the eye itself, which is most likely in a patient with cardiovascular disease, high blood pressure or diabetes. Mrs. Snell suffered from the latter two conditions, although only to the extent that they were controlled by diet rather than medication. Mrs. Snell also suffered from severe glaucoma, which over a long period can also cause optic nerve atrophy. The plaintiff's expert testified that it was unusual to have chronic glaucoma in just one eye, like Mrs. Snell, unless there has been an intervention of some type. The only intervention of which the expert was aware was the operation itself.

Neither expert was able to express with certainty an opinion as to what caused the atrophy in this case or when it occurred.

The respondent succeeded in an action against the appellant in the Court of Queen's Bench of New Brunswick, the trial judge finding that the appellant was liable in negligence: (1986), 1986 CanLII 5365 (NB QB), 77 N.B.R. (2d) 222. The appellant's appeal to the Court of Appeal of New Brunswick was dismissed: (1988), 1988 CanLII 8128 (NB CA), 84 N.B.R. (2d) 401.

Judgments

Court of Queen's Bench

The respondent sued claiming in both negligence and battery. Considering his conclusion with respect to negligence, the trial judge did not make a finding with respect to battery.

The trial judge accepted the appellant's evidence that the respondent did not develop the hardening of the eye ordinarily associated with a retrobulbar bleed. He concluded, however, that the appellant had thought that there was a small retrobulbar bleed and that he would have to work quickly before it exerted pressure on the content of the eye. He remarked that the appellant's decision "went beyond a judgment call" and he accepted the evidence of the expert Dr. Samis that, where there is bleeding other than the obvious pinprick of the needle, the operation should be aborted as it is impossible to determine the location of the bleeding.

Turnbull J. was of the opinion that once the appellant had made the decision to proceed with the operation the onus shifted to him under the doctrine of res ipsa loquitur. In so concluding, he relied upon the decision of the Supreme Court of Canada in Finlay v. Auld, 1973 CanLII 188 (SCC), [1975] 1 S.C.R. 338. However, as the defendant could provide an explanation of the occurrence equally consistent with there being no negligence, the plaintiff could not succeed under this doctrine.

Although neither of the expert witnesses called by the parties could say whether the operation had caused the injury, the trial judge was satisfied that the facts of the case at bar brought it "within an emerging branch of the law of causation" whereby the onus to disprove causation shifts to the defendant in certain circumstances. In this regard, he relied on the decision of the House of Lords in McGhee v. National Coal Board, [1973] 1 W.L.R. 1. He concluded that the respondent had prima facie proved that the appellant's actions had caused her injury and that the appellant had not satisfied the onus that had shifted to him. Therefore causation, and negligence, was made out.

Court of Appeal

In the opinion of the Court of Appeal, the evidence supported the trial judge's conclusion that the appellant recognized a small retrobulbar haemorrhage following his administration of the anaesthetic. Hoyt J.A. considered Wilsher v. Essex Area Health Authority, [1987] 2 W.L.R. 425 (C.A.), and approved of the analysis of McGhee, supra, by Mustill L.J. According to Mustill L.J. if it is established that conduct of a certain kind materially adds to the risk of injury, if the defendant engages in such conduct in breach of a common law duty, and if the injury is the kind to which the conduct related, then the defendant is taken to have caused the injury even though the existence and extent of the contribution made by the breach cannot be ascertained. The Court of Appeal found that Turnbull J. was correct in applying the decision of the House of Lords in McGhee. The conduct of the appellant, in not aborting the operation, made it more likely that the respondent, to whom the appellant owed a duty, would lose the sight in her right eye.

The Issues

1. Is the burden of proof of causation in a medical malpractice case on the plaintiff and if so, how is it satisfied?

2. If the burden of proof of causation is on the plaintiff, did the trial judge infer causation in this case and if not, ought he to have done so?

Causation -- Principles

Both the trial judge and the Court of Appeal relied on McGhee, which (subject to its re-interpretation in the House of Lords in Wilsher) purports to depart from traditional principles in the law of torts that the plaintiff must prove on a balance of probabilities that, but for the tortious conduct of the defendant, the plaintiff would not have sustained the injury complained of. In view of the fact that McGhee has been applied by a number of courts in Canada to reverse the ordinary burden of proof with respect to causation, it is important to examine recent developments in the law relating to causation and to determine whether a departure from well-established principles is necessary for the resolution of this appeal.

The traditional approach to causation has come under attack in a number of cases in which there is concern that due to the complexities of proof, the probable victim of tortious conduct will be deprived of relief. This concern is strongest in circumstances in which, on the basis of some percentage of statistical probability, the plaintiff is the likely victim of the combined tortious conduct of a number of defendants, but cannot prove causation against a specific defendant or defendants on the basis of particularized evidence in accordance with traditional principles. The challenge to the traditional approach has manifested itself in cases dealing with non-traumatic injuries such as man-made diseases resulting from the widespread diffusion of chemical products, including product liability cases in which a product which can cause injury is widely manufactured and marketed by a large number of corporations. The developments in this area are admirably surveyed by Professor John G. Fleming in "Probabilistic Causation in Tort Law" (1989), 68 Can. Bar Rev. 661. Except for the United States, this challenge has had little impact in the common law jurisdictions. Even in the United States, its effect has been sporadic. In the area referred to above, courts in some states have experimented with a theory of probability which requires proof on the basis of probability at less than 51 percent, and apportionment of liability among defendant manufacturers of the product in question on the basis of market share. See Fleming, op. cit.; Sindell v. Abbott Laboratories, 607 P.2d 924 (Cal. 1980).

Although, to date, these developments have had little impact in other common law countries, it has long been recognized that the allocation of the burden of proof is not immutable. The legal or ultimate burden of proof is determined by the substantive law "upon broad reasons of experience and fairness": 9 Wigmore on Evidence, {SS} 2486, at p. 292. In a civil case, the two broad principles are:

1.that the onus is on the party who asserts a proposition, usually the plaintiff;

2.that where the subject matter of the allegation lies particularly within the knowledge of one party, that party may be required to prove it.

This Court has not hesitated to alter the incidence of the ultimate burden of proof when the underlying rationale for its allocation is absent in a particular case: see National Trust Co. v. Wong Aviation Ltd., 1969 CanLII 11 (SCC), [1969] S.C.R. 481. This flexibility extends to the issue of causation. In Cook v. Lewis, 1951 CanLII 26 (SCC), [1951] S.C.R. 830, the plaintiff was struck by a bullet fired from the gun of one of his two companions. The evidence supported the theory that they fired simultaneously in the plaintiff's direction when they knew his location. The plaintiff could not prove which shot struck him and therefore on traditional rules, he would fail. The basic premises referred to above did not make good legal sense in this instance. Both defendants were negligent and each asserted that his negligence did not cause the injury. Since the plaintiff could establish that one of them caused the injury, why should not the defendants be required to exculpate themselves by proving their assertions, and failing that, be held equally liable? Applying the reasoning in Summers v. Tice (1948), 5 A.L.R. (2d) 91, this Court concluded that if it could not be determined which defendant fired the shot that struck the plaintiff, both defendants must be found liable.

Proof of causation in medical malpractice cases is often difficult for the patient. The physician is usually in a better position to know the cause of the injury than the patient. On the basis of the second basic principle referred to above, there is an argument that the burden of proof should be allocated to the defendant. In some jurisdictions, this has occurred to an extent by operation of the principle of res ipsa loquitur: Cross on Evidence (6th ed. 1985), at p. 138. In Canada, the rule has been generally regarded as a piece of circumstantial evidence which does not shift the burden of proof: see Interlake Tissue Mills Co. v. Salmon and Beckett, 1948 CanLII 74 (ON CA), [1949] 1 D.L.R. 207 (Ont. C.A.); Cudney v. Clements Motor Sales Ltd., 1969 CanLII 200 (ON CA), [1969] 2 O.R. 209 (C.A.); Kirk v. McLaughlin Coal & Supplies Ltd., 1967 CanLII 345 (ON CA), [1968] 1 O.R. 311 (C.A.); Jackson v. Millar (1972), 1972 CanLII 44 (ON CA), 31 D.L.R. (3d) 263 (Ont. C.A.). As the rule was properly held not to be applicable in this case and no argument was directed to this issue, I will refrain from commenting further upon it.

This brings me to the McGhee case and its influence on subsequent cases, particularly in the medical malpractice field. The appellant contracted dermatitis while employed as a labourer emptying pipe kilns. This work exposed him to clouds of abrasive dust. His employer provided no washing facilities with the result that the appellant would ride home on his bicycle caked with grime and sweat. He sued his employer, the respondent, for negligence. The medical evidence showed that the dermatitis was caused by the working conditions and that the longer the exposure to dust, the greater the chance of developing dermatitis. The medical evidence could not attribute the dermatitis to the additional exposure after work. The appellant's expert could not say that if washing facilities had been provided, the appellant would not have contracted the disease. A breach of duty was found with respect to the failure to provide washing facilities but not with respect to the conditions under which the kilns were operated. The Lord Ordinary dismissed the action on the ground that it had not been shown that the breach of duty caused or contributed to the injury. An appeal to the First Division of the Court of Session failed but an appeal was allowed by the House of Lords.

Of the five speeches in the House of Lords, only Lord Wilberforce advocated a reversal of the burden of proof. He did so in the following passage which has been the basis of decisions in a number of cases both in Canada and in Britain. He states at p. 6:

First, it is a sound principle that where a person has, by breach of a duty of care, created a risk, and injury occurs within the area of that risk, the loss should be borne by him unless he shows that it had some other cause.

He added at p. 7:

And I must say that, at least in the present case, to bridge the evidential gap by inference seems to me something of a fiction, since it was precisely this inference which the medical expert declined to make.

Two theories of causation emerge from an analysis of the speeches of the Lords in this case. The first, firmly espoused by Lord Wilberforce, is that the plaintiff need only prove that the defendant created a risk of harm and that the injury occurred within the area of the risk. The second is that in these circumstances, an inference of causation was warranted in that there is no practical difference between materially contributing to the risk of harm and materially contributing to the harm itself.

The speeches were subjected to a careful examination and interpretation in Wilsher v. Essex Area Health Authority, [1988] 2 W.L.R. 557, by Lord Bridge when some fifteen years later, the House of Lords revisited the issue. The plaintiff claimed damages from the defendant health authority for negligence in medical treatment which resulted in a condition of the eyes leading to blindness. A likely cause of the condition but not a definite one, in the opinion of medical experts, was too much oxygen. The plaintiff proved that for a period of time he was supersaturated with oxygen. A number of different factors other than excessive oxygen could have caused or contributed to the injury. The expert evidence was conflicting. The trial judge applied McGhee and held the defendant liable since it had failed to prove that the plaintiff's condition had not resulted from its negligence. The Court of Appeal dismissed the appeal by a majority judgment with the Vice-Chancellor dissenting. The House of Lords allowed the appeal and directed a new trial. Lord Bridge, delivering the unanimous judgment of the court, reaffirmed the principle that the burden of proving causation rested on the plaintiff. Since the trial judge had not made the relevant finding of fact to sort out the conflicting evidence, a new trial was directed on this basis. Lord Bridge interpreted McGhee as espousing no new principle. Instead, McGhee was explained as promoting a robust and pragmatic approach to the facts to enable an inference of negligence to be drawn even though medical or scientific expertise cannot arrive at a definitive conclusion. In the course of his reasons, Lord Bridge stated at p. 569:

The conclusion I draw from these passages is that McGhee v. National Coal Board [1973] 1 W.L.R. 1 laid down no new principle of law whatever. On the contrary, it affirmed the principle that the onus of proving causation lies on the pursuer or plaintiff. Adopting a robust and pragmatic approach to the undisputed primary facts of the case, the majority concluded that it was a legitimate inference of fact that the defenders' negligence had materially contributed to the pursuer's injury. The decision, in my opinion, is of no greater significance than that and to attempt to extract from it some esoteric principle which in some way modifies, as a matter of law, the nature of the burden of proof of causation which a plaintiff or pursuer must discharge once he has established a relevant breach of duty is a fruitless one.

Earlier, at p. 567, he stated:

But where the layman is told by the doctors that the longer the brick dust remains on the body, the greater the risk of dermatitis, although the doctors cannot identify the process of causation scientifically, there seems to be nothing irrational in drawing the inference, as a matter of common sense, that the consecutive periods when brick dust remained on the body probably contributed cumulatively to the causation of the dermatitis. I believe that a process of inferential reasoning on these general lines underlies the decision of the majority in McGhee's case.

Lord Bridge concluded with a caution at p. 571:

But, whether we like it or not, the law, which only Parliament can change, requires proof of fault causing damage as the basis of liability in tort. We should do society nothing but disservice if we made the forensic process still more unpredictable and hazardous by distorting the law to accommodate the exigencies of what may seem hard cases.

Canadian cases decided after McGhee but before Wilsher tended to follow McGhee by adopting either the reversal of onus or the inference interpretation. Which interpretation was adopted made no practical difference because even when the latter approach was applied, the creation of the risk by the defendant's breach of duty was deemed to have established a prima facie case, thus shifting the onus to the defendant. Powell v. Guttman (1978), 1978 CanLII 1933 (MB CA), 89 D.L.R. (3d) 180 (Man. C.A.) and Letnick v. Toronto (Municipality of Metropolitan), 1988 CanLII 9438 (FCA), [1988] 2 F.C. 399 (C.A.), applied the reversal of proof theory. In Dalpe v. City of Edmundston (1979), 1979 CanLII 3239 (NB CA), 25 N.B.R. (2d) 102 (S.C., App. Div.), the New Brunswick Court of Appeal, in a flooding case in which negligence was alleged against a municipal authority, held that in circumstances in which a risk of the type of harm which in fact occurred had been created, causation should be inferred in the absence of evidence to the contrary on the part of the defendant. In Nowsco Well Service Ltd. v. Canadian Propane Gas & Oil Ltd. (1981), 1981 CanLII 2034 (SK CA), 122 D.L.R. (3d) 228 (Sask. C.A.), the Saskatchewan Court of Appeal applied McGhee on the basis that proof that the breach of duty which gave rise to the risk "is prima facie proof that the fire was caused by the escape of propane gas" (p. 248).

Decisions in Canada after Wilsher accept its interpretation of McGhee. In the circumstances in which McGhee had been previously interpreted to support a reversal of the burden of proof, an inference was now permissible to find causation, notwithstanding that causation was not proved by positive evidence: see Rendall v. Ewert (1989), 1989 CanLII 232 (BC CA), 38 B.C.L.R. (2d) 1 (C.A.); Kitchen v. McMullen (1989), 1989 CanLII 218 (NB CA), 100 N.B.R. (2d) 91 (C.A.); Westco Storage Ltd. v. Inter-City Gas Utilities Ltd., 1989 CanLII 7270 (MB CA), [1989] 4 W.W.R. 289 (Man. C.A.); and Haag v. Marshall, 1989 CanLII 236 (BC CA), [1990] 1 W.W.R. 361 (B.C.C.A.).

The question that this Court must decide is whether the traditional approach to causation is no longer satisfactory in that plaintiffs in malpractice cases are being deprived of compensation because they cannot prove causation where it in fact exists.

Causation is an expression of the relationship that must be found to exist between the tortious act of the wrongdoer and the injury to the victim in order to justify compensation of the latter out of the pocket of the former. Is the requirement that the plaintiff prove that the defendant's tortious conduct caused or contributed to the plaintiff's injury too onerous? Is some lesser relationship sufficient to justify compensation? I have examined the alternatives arising out of the McGhee case. They were that the plaintiff simply prove that the defendant created a risk that the injury which occurred would occur. Or, what amounts to the same thing, that the defendant has the burden of disproving causation. If I were convinced that defendants who have a substantial connection to the injury were escaping liability because plaintiffs cannot prove causation under currently applied principles, I would not hesitate to adopt one of these alternatives. In my opinion, however, properly applied, the principles relating to causation are adequate to the task. Adoption of either of the proposed alternatives would have the effect of compensating plaintiffs where a substantial connection between the injury and the defendant's conduct is absent. Reversing the burden of proof may be justified where two defendants negligently fire in the direction of the plaintiff and then by their tortious conduct destroy the means of proof at his disposal. In such a case it is clear that the injury was not caused by neutral conduct. It is quite a different matter to compensate a plaintiff by reversing the burden of proof for an injury that may very well be due to factors unconnected to the defendant and not the fault of anyone.

The experience in the United States tells us that liberalization of rules for recovery in malpractice suits contributed to the medical malpractice crisis of the 1970's: See Glen O. Robinson, "The Medical Malpractice Crisis of the 1970's: A Retrospective", 49 Law & Contemp. Probs., Spring 1986, p. 5, at p. 18. Insurance premiums in some states increased up to 500 percent. Some major commercial insurers withdrew from the market entirely, creating serious problems of availability of insurance. See James R. Posner, "Trends in Medical Malpractice Insurance, 1970-1985", 49 Law & Contemp. Probs., Spring 1986, p. 37, at p. 38.

In Britain, proposals to reverse the burden of proof in malpractice cases which gained momentum by virtue of the McGhee case were not adopted. In 1978, the Royal Commission on Civil Liability and Compensation for Personal Injury (Pearson Report, vol. I) reported as follows at p. 285:

Some witnesses suggested that, if the burden of proof were reversed, the patient's difficulties in obtaining and presenting his evidence would be largely overcome. It was said that doctors were in a better position to prove absence of negligence than patients were to establish liability. At the Council of Europe colloquy, however, although it was agreed that the patient was at a disadvantage when he sought to establish a claim, serious doubts were expressed on the desirability of making a radical change in the burden of proof. We share these doubts. We think that there might well be a large increase in claims, and although many would be groundless, each one would have to be investigated and answered. The result would almost certainly be an increase in defensive medicine.

The Wilsher decision in the House of Lords which followed ensured that the common law did not undermine this recommendation.

I am of the opinion that the dissatisfaction with the traditional approach to causation stems to a large extent from its too rigid application by the courts in many cases. Causation need not be determined by scientific precision. It is, as stated by Lord Salmon in Alphacell Ltd. v. Woodward, [1972] 2 All E.R. 475, at p. 490:

... essentially a practical question of fact which can best be answered by ordinary common sense rather than abstract metaphysical theory.

Furthermore, as I observed earlier, the allocation of the burden of proof is not immutable. Both the burden and the standard of proof are flexible concepts. In Blatch v. Archer (1774), 1 Cowp. 63, 98 E.R. 969, Lord Mansfield stated at p. 970:

It is certainly a maxim that all evidence is to be weighed according to the proof which it was in the power of one side to have produced, and in the power of the other to have contradicted.

In many malpractice cases, the facts lie particularly within the knowledge of the defendant. In these circumstances, very little affirmative evidence on the part of the plaintiff will justify the drawing of an inference of causation in the absence of evidence to the contrary. This has been expressed in terms of shifting the burden of proof. In Cummings v. City of Vancouver (1911), 1911 CanLII 265 (BC CA), 1 W.W.R. 31 (B.C.C.A.), Irving J.A. stated at p. 34:

Stephens [sic] in his Digest (Evidence Act, 1896) says: "In considering the amount of evidence necessary to shift the burden of proof, the Court has regard to the opportunities of knowledge with respect to the fact to be proved, which may be possessed by the parties respectively."

Hollis v. Young (1909) 1 K.B., 629, illustrates the rule that very little affirmative evidence will be sufficient where the facts lie almost entirely within the knowledge of the other side.

In Dunlop Holdings Ltd.'s Application, [1979] R.P.C. 523 (C.A.), Buckley L.J. affirmed this principle in the following terms at p. 544:

Where the relevant facts are peculiarly within the knowledge of one party, it is perhaps relevant to have in mind the rule as stated in Stephen's Digest, which is cited at page 86 of Cross on Evidence [3rd ed.]:

"In considering the amount of evidence necessary to shift the burden of proof, the court has regard to the opportunities of knowledge with respect to the facts to be proved which may be possessed by the parties respectively".

"This does not mean", Sir Rupert continues, "that the peculiar means of knowledge of one of the parties relieves the other of the burden of adducing some evidence with regard to the facts in question, although very slight evidence will often suffice". [Emphasis added.]

See also Diamond v. British Columbia Thoroughbred Breeders' Society (1965), 1965 CanLII 474 (BC SC), 52 D.L.R. (2d) 146 (B.C.S.C.), at p. 158; Pleet v. Canadian Northern Quebec R. Co. (1921), 1921 CanLII 518 (ON CA), 64 D.L.R. 316 (Ont. S.C., App. Div.), at pp. 319-20; and Guaranty Trust Co. of Canada v. Mall Medical Group, 1969 CanLII 78 (SCC), [1969] S.C.R. 541, at p. 545.

These references speak of the shifting of the secondary or evidential burden of proof or the burden of adducing evidence. I find it preferable to explain the process without using the term secondary or evidential burden. It is not strictly accurate to speak of the burden shifting to the defendant when what is meant is that evidence adduced by the plaintiff may result in an inference being drawn adverse to the defendant. Whether an inference is or is not drawn is a matter of weighing evidence. The defendant runs the risk of an adverse inference in the absence of evidence to the contrary. This is sometimes referred to as imposing on the defendant a provisional or tactical burden. See Cross, op. cit., at p. 129. In my opinion, this is not a true burden of proof, and use of an additional label to describe what is an ordinary step in the fact-finding process is unwarranted.

The legal or ultimate burden remains with the plaintiff, but in the absence of evidence to the contrary adduced by the defendant, an inference of causation may be drawn although positive or scientific proof of causation has not been adduced. If some evidence to the contrary is adduced by the defendant, the trial judge is entitled to take account of Lord Mansfield's famous precept. This is, I believe, what Lord Bridge had in mind in Wilsher when he referred to a "robust and pragmatic approach to the ... facts" (p. 569).

It is not therefore essential that the medical experts provide a firm opinion supporting the plaintiff's theory of causation. Medical experts ordinarily determine causation in terms of certainties whereas a lesser standard is demanded by the law. As pointed out in Louisell, Medical Malpractice, vol. 3, the phrase "in your opinion with a reasonable degree of medical certainty," which is the standard form of question to a medical expert, is often misunderstood. The author explains, at p. 25-57, that:

Many doctors do not understand the phrase ... as they usually deal in "certainties" that are 100% sure, whereas "reasonable" certainties which the law requires need only be more probably so, i.e., 51%.

In Harvey, Medical Malpractice (1973), the learned author states at p. 169:

Some courts have assumed an unrealistic posture in requiring that the medical expert state conclusively that a certain act caused a given result. Medical testimony does not lend itself to precise conclusions because medicine is not an exact science.

The respective functions of the trier of fact and the expert witness are distinguished by Brennan J. of the United States Supreme Court in the following passage in Sentilles v. Inter-Caribbean Shipping Corp., 361 U.S. 107 (1959), at pp. 109-10:

The jury's power to draw the inference that the aggravation of petitioner's tubercular condition, evident so shortly after the accident, was in fact caused by that accident, was not impaired by the failure of any medical witness to testify that it was in fact the cause. Neither can it be impaired by the lack of medical unanimity as to the respective likelihood of the potential causes of the aggravation, or by the fact that other potential causes of the aggravation existed and were not conclusively negated by the proofs. The matter does not turn on the use of a particular form of words by the physicians in giving their testimony. The members of the jury, not the medical witnesses, were sworn to make a legal determination of the question of causation. They were entitled to take all the circumstances, including the medical testimony, into consideration.

With respect, it was the failure to appreciate this distinction which led Lord Wilberforce in McGhee to suggest bridging the evidential gap by reversing the burden of proof. He writes at p. 7:

... to bridge the evidential gap by inference seems to me something of a fiction, since it was precisely this inference which the medical expert declined to make.

In Wilsher, supra, Lord Bridge gave effect to this difference when he explained McGhee at p. 567:

... where the layman is told by the doctors that the longer the brick dust remains on the body, the greater the risk of dermatitis, although the doctors cannot identify the process of causation scientifically, there seems to be nothing irrational in drawing the inference, as a matter of common sense, that the consecutive periods when brick dust remained on the body contributed cumulatively to the causation of the dermatitis. I believe that a process of inferential reasoning on these general lines underlies the decision of the majority in McGhee's case. [Emphasis added.]

The issue, then, in this case is whether the trial judge drew an inference that the appellant's negligence caused or contributed to the respondent's injury, or whether, applying the above principles, he would or ought to have drawn such an inference.

Causation in This Case

The trial judge found that the appellant was negligent in continuing with the operation when retrobulbar bleeding occurred. This finding is not contested and is fully supported by the evidence. An opinion expressed by both the appellant and his assistant, Dr. Quinn, that what occurred was a "lid bleed" was rejected by the trial judge. It was common ground that the respondent's blindness occurred due to atrophy or death of the optic nerve which was occasioned by a stroke. A stroke is the destruction of a blood vessel due to an interruption of the blood supply. There were two possible causes of the stroke, one of which was natural and the other due to continuing the operation. Dr. Regan, the appellant's expert, testified as follows on cross-examination:

Q.But it's not the only thing. As you indicated earlier in your testimony a retrobulbar hemorrhage can also place pressure on the optic nerve.

A.Yes.

Q.And if it becomes aggravated for whatever reason or in whatever fashion it can eventually harm the optic nerve, even cause stroke?

A.Could.

Q.Well the stroke could occur due to some systemic disease of the patient as well, couldn't it?

A.By stroke you're talking about destruction of a vessel?

Q.Yes.

A.Yes.

Q.That could happen either as a result of a retrobulbar bleed which continued or got aggravated, or naturally. It could occur naturally without any traumatic interference.

A.That's correct.

Earlier in chief, Dr. Regan gave the following answer:

Q.Is it possible to tell what caused the atrophy of the optic nerve in your opinion?

A.I would think probably the base cause is the retrobulbar hemorrhage, the fact that there was enough pressure behind the eye at some point that caused all this bleeding, that this may have been sufficient to compromise the blood supply to the optic nerve and result in the optic damage, but I can't tell you this for sure, it's just a .. in reading the charts this may well be what it is. Certainly there are people that have retrobulbar hemorrhages who do not have any compromise of the vascular supply and do not end up with nerve damage.

The appellant testified in cross-examination as follows:

Q.Right. But we're on common ground that the most likely cause of blindness in Mrs. Snell's case was an ocular occlusion or an occlusion, a stroke, affecting the blood supply to the optic nerve.

A. Yes.

Q.The most reasonable explanation.

In re-examination he gave the following answer:

Q.The question, doctor, is that there's no evidence, is there, that anything other than the operation, the whole operation, was a factor in causing the stroke which Mrs. Snell suffered. There's no evidence of anything external to the operation that caused that stroke, is there?

A.Well it's partially semantics here but there's a very .. in medical terms there's a very distinct definition or distinction between the operation and the anesthetic so that if you're including the anesthetic in your general term operation, then fine, I can agree, but in particular, there's no evidence that the operation per se, other than the anesthetic, involved or caused a problem with the stroke. There are the other systemic problems that Mrs. Snell has that may possibly have caused the stroke but there's no indication that they did. [Emphasis added.]

The anaesthetic, of course, was the needle which caused the retrobulbar bleeding. The trial judge found that it should have been recognized as such and the operation terminated. If it had, the bleeding would have been stanched. Continuing with the operation permitted the bleeding to continue undetected because the eye was occluded by blood and patched. Palpitation of the eye to test for hardness apparently failed to disclose the haemorrhaging. A crucial finding of the trial judge was the following at pp. 228-29:

Neither Dr. Samis nor Dr. Regan could give an opinion as to what caused the atrophy to the optic nerve. Neither doctor could state when the atrophy occurred since it was some eight months before Dr. Farrell could see the optic nerve because of the blood in the anterior chamber. It was atrophied when he first saw it in August 1984. Neither doctor was able to express an opinion that the operation contributed to the atrophy except to the extent that the retrobulbar hemorrhage which may have been stanched may have been reopened by the operation. Perhaps what eventually did happen was going to happen once the injection was completed. The retrobulbar bleeding commenced at that time. It may have been a slow hemorrhage that had not stopped and was not going to stop. The hemorrhage would have been allowed to flow more freely with the removal of the tamponade effect of opening the cornea. I cannot go beyond this since neither doctor did and I should not speculate in matters of medical opinion. Both doctors agree that the atrophy resulted from a loss of its own blood supply. This may have been as a result of natural causes although I am not inclined to this view. The operation would assist bleeding while the cornea remained open. [Emphasis added.]

It is significant that this finding virtually rules out natural causes as did the appellant. The trial judge then continued at p. 241:

Dr. Farrell greatly increased the risk of injury to Mrs. Snell's eye by operating when he knew she had a retrobulbar bleed. Bleeding in the retrobulbar area was facilitated during the operation. No one can say what happened or with certainty when it happened, because the bleeding from the cataract removal prohibited the doctors from seeing the optic nerve. I am of the opinion that the defendant was "asking for trouble" by operating when he knew his patient had a retrobulbar bleed and that the increased risk was followed by injury in the same area of risk.

I am of the opinion that the plaintiff has prima facie proved that the defendant's actions caused the plaintiff's injury and that the defendant has not satisfied the onus that shifted to him. [Emphasis added.]

The finding in the last paragraph can be read as a finding of causation inferred from the circumstances and in the absence of evidence to the contrary in satisfaction of the evidential burden cast upon the defendant. Or it could be interpreted as accepting Lord Wilberforce's formulation in McGhee which reverses the ultimate burden upon finding that a risk was created and an injury occurred within the area of the risk. If the former was intended, I am of the opinion that such an inference was fully warranted on the evidence. On the other hand, if the latter is the interpretation to be placed on that statement, and I am inclined to think that it is, then I am satisfied that had the trial judge applied the principles referred to above he would have drawn an inference of causation between the appellant's negligence and the injury to the respondent.

The appellant was present during the operation and was in a better position to observe what occurred. Furthermore, he was able to interpret from a medical standpoint what he saw. In addition, by continuing the operation which has been found to constitute negligence, he made it impossible for the respondent or anyone else to detect the bleeding which is alleged to have caused the injury. In these circumstances, it was open to the trial judge to draw the inference that the injury was caused by the retrobulbar bleeding. There was no evidence to rebut this inference. The fact that testing the eye for hardness did not disclose bleeding is insufficient for this purpose. If there was any rebutting evidence it was weak, and it was open to the trial judge to find causation, applying the principles to which I have referred.

I am confident that had the trial judge not stated that "I cannot go beyond this since neither doctor did and I should not speculate", he would have drawn the necessary inference. In stating the above, he failed to appreciate that it is not essential to have a positive medical opinion to support a finding of causation. Furthermore, it is not speculation but the application of common sense to draw such an inference where, as here, the circumstances, other than a positive medical opinion, permit.

While this Court does not ordinarily make findings of fact, this course is fully justified in this case. First, I am of the opinion that the trial judge either made the necessary finding or would have but for error of law. Second, it would be a disservice to all to send this case back for a new trial when the evidence is not essentially in conflict. I note that in Wilsher, the House of Lords refrained from deciding the case only because the evidence of the experts was seriously in conflict. That is not the case here.

In the result, I would dismiss the appeal with costs.

Appeal dismissed with costs.

Solicitors for the appellant: Gilbert, McGloan, Gillis, Saint John.

Solicitors for the respondent: McKelvey, Macaulay, Machum, Saint John.

• Chief Justice at the time of hearing.