A decision of the Privy Council on appeal from the Court of Appeal of Bermuda, the judgment in Williams v The Bermuda Hospitals Board  UKPC 4 was delivered yesterday. The short 13 page judgment was of Lady Hale, Lord Clarke, Lord Hughes and Lord Hodge, delivered by Lord Toulson.
The reasons include discussion of Bonnington Castings Ltd v Wardlaw, Hotson v East Berkshire Health Authority and Bailey v Ministry of Defence. Perhaps of greatest general interest will be the caution expressed, near the end of the reasons for judgment, about inferring causation from proof of heightened risk.
Initially suffering acute appendicitis, there was a negligent delay in performing a CT scan for Mr Williams who, because of sepsis, suffered myocardial ischaemia and lung complications (at ). The trial judge found for the defendant on the basis that the claimant failed to prove that the complications he suffered were probably caused by the delay (at ). The Court of Appeal reversed the decision, as summarised at :
…. the trial judge was in error “by raising the bar unattainably high” in his finding that Mr Williams had failed to prove his case. The proper test of causation, he said, was “not whether the negligent delay and inadequate system caused the injury to [Mr Williams] but rather whether the breaches of duty by [the hospital board] contributed materially to the injury”. That the breaches contributed materially to the injury was in his view beyond argument. He stated that the “but for” test is sometimes relaxed to enable a claimant to overcome the causation hurdle when it might otherwise seem unjust to require the claimant to prove the impossible, and he referred to Bailey v Ministry of Defence  1 WLR 1052 as a case in which the “but for” rule was modified.
The Board of the Privy Council dismissed the appeal, concluding at  – :
41. In the present case the judge found that injury to the heart and lungs was caused by a single known agent, sepsis from the ruptured appendix. The sepsis developed incrementally over a period of approximately six hours, progressively causing myocardial ischaemia. (The greater the accumulation of sepsis, the greater the oxygen requirement.) The sepsis was not divided into separate components causing separate damage to the heart and lungs. Its development and effect on the heart and lungs was a single continuous process, during which the sufficiency of the supply of oxygen to the heart steadily reduced.
42. On the trial judge’s findings, that process continued for a minimum period of two hours 20 minutes longer than it should have done. In the judgment of the Board, it is right to infer on the balance of probabilities that the hospital board’s negligence materially contributed to the process, and therefore materially contributed to the injury to the heart and lungs.
Commenting on Bailey v Ministry of Defence (and whether that case is properly described as a departure from the but for test), the Board at  said:
47. In the view of the Board, on those findings of primary fact Foskett J was right to hold the hospital responsible in law for the consequences of the aspiration. As to the parallel weakness of the claimant due to her pancreatitis, the case may be seen as an example of the well known principle that a tortfeasor takes his victim as he finds her. The Board does not share the view of the Court of Appeal that the case involved a departure from the “but-for” test. The judge concluded that the totality of the claimant’s weakened condition caused the harm. If so, “but-for” causation was established. The fact that her vulnerability was heightened by her pancreatitis no more assisted the hospital’s case than if she had an egg shell skull.
Finally and perhaps of greatest interest is the caution about the use of ‘doubling the risk‘ as a tool in deciding questions of causation. The Board said at :
48. Finally, reference was made during the argument to the “doubling of risk” test which has sometimes been used or advocated as a tool used in deciding questions of causation. The Board would counsel caution in its use. As Baroness Hale of Richmond said in Sienkiewicz at para 170, evaluation of risk can be important in making choices about future action. This is particularly so in the medical field, where a practitioner will owe a duty to the patient to see that the patient is properly informed about the potential risks of different forms of treatment (or non-treatment). Use of such evidence, for example epidemiological evidence, to determine questions of past fact is rather different. That is not to deny that it may sometimes be very helpful. If it is a known fact that a particular type of act (or omission) is likely to have a particular effect, proof that the defendant was responsible for such an act (or omission) and that the claimant had what is the usual effect will be powerful evidence from which to infer causation, without necessarily requiring a detailed scientific explanation for the link. But inferring causation from proof of heightened risk is never an exercise to apply mechanistically. A doubled tiny risk will still be very small.