This important case makes two broad points:
- that the doctrine of res ipsa loquitur works in simple medical negligence cases; but
- that in more complex cases it is not directly applicable because there will almost certainly be medical evidence to strengthen or weaken the claimant’s case and therefore the court will not be drawing the res ipsa inference.
After reviewing the authorities Brooke L.J. said,
It is likely to be a very rare medical negligence case in which the defendants take the risk of calling no factual evidence, when such evidence is available to them, of the circumstances surrounding a procedure which led to an unexpected outcome for a patient…
(1) In its purest form the maxim [rers ipsa loquitur] applies where the [claimant] relies on the res (the thing itself) to raise the inference of negligence, which is supported by ordinary human experience, with no need for expert evidence.
(2) In principle, the maxim can be applied in that form in simple situations in the medical negligence field…
(3) In practice, in contested medical negligence cases the evidence of the [claimant], which establishes the res , is likely to be buttressed by expert evidence to the effect that the matter complained does not ordinarily occur in the absence of negligence.
(4) The position may then be reached at the close of the [claimant’s] case that the judge would be entitled to infer negligence on the defendant’s part unless the defendant adduces evidence which discharges this inference.
(5) This evidence may be to the effect that there is a plausible explanation of what may have happened which does not connote any negligence on the defendant’s part. The explanation must be a plausible one and not a theoretically or remotely possible one, but the defendant certainly does not have to prove that his explanation is more likely to be correct than any other. If the [claimant] has no other evidence of negligence to rely on, his claim will then fail.
(6) Alternatively, the defendant’s evidence may satisfy the judge on the balance of probabilities that he did exercise proper care If the untoward outcome is extremely rare, or is impossible to explain in the light of the current state of medical knowledge, the judge will be bound to exercise great care in evaluating the evidence before making such a finding, but if he does so, the prima facie inference of negligence is rebutted and the plaintiff’s claim will fail…
(7) It follows from all this that although in very simple situations the res may speak for itself at the end of the lay evidence adduced on behalf of the plaintiff, in practice the inference is then buttressed by expert evidence adduced on his behalf, and if the defendant were to call no evidence, the judge would be deciding the case on inferences he was entitled to draw from the whole of the evidence (including the expert evidence), and not on the application of the maxim in its purest form.
In O’Connor v Pennine Acute Hospitals NHS Trust  EWCA Civ 1224 the trial judge was held not to be at fault in taking the Ratcliffe factors into account where the defendant had not offered an alternative explanation to that put forward by the Claimant.