Marshall v Schembri

In a medical negligence claim, a claimant need prove only that the breach probably caused the injury or death. The claimant need not establish the precise mechanism by which the outcome would have been avoided. Where the counterfactual course of events contains substantial uncertainty, the court must assess the evidence as a whole, including expert evidence and relevant medical literature, using a common-sense and pragmatic approach. Statistical evidence must be treated with care, but may assist when considered with the clinical evidence. A number of possible mechanisms cannot simply be aggregated into a probability; the overall evidence must nevertheless be considered to determine whether causation is more likely than not.

The defendant, a general practitioner, admitted that he negligently failed to refer Doreen Marshall directly to hospital when she presented with chest pain and breathlessness and a history of pulmonary embolism. She died the following morning from a massive pulmonary embolism. Damages had been agreed, subject to liability.

The issue was whether the claimant had proved that Mrs Marshall would probably have survived had she been referred to hospital. The court considered alternative counterfactual mechanisms, including anticoagulation, monitoring, thrombolysis and treatment following cardiogenic shock or cardiac arrest.

1. Causation and burden of proof. The claimant bore the burden of proving causation on the balance of probabilities. The claimant did not have to prove the precise medical mechanism by which hospital admission would have avoided death. It was sufficient to prove that survival would probably have occurred.
2. Specific mechanisms. The claimant failed to prove that progressive pulmonary emboli probably formed during the night. Even if such emboli had formed, it was not proved that deterioration would probably have reached the threshold for thrombolysis before collapse. Nor was it proved that thrombolysis and CPR would probably have saved Mrs Marshall after cardiac arrest. Heparin alone would not probably have prevented death, although it would probably have restricted clot growth and improved the prospects of survival.
3. Assessment of the evidence as a whole. The court considered the expert evidence, medical literature, the likely effect of hospital monitoring and treatment, and the low mortality of comparable hospitalised patients. The precise counterfactual sequence remained uncertain, but the evidence showed that Mrs Marshall would probably have survived had she been admitted to hospital. The court adopted a common-sense and pragmatic approach, while recognising the limitations of the statistical evidence.
4. The authorities on proof of causation, including Vaile v London Borough of Havering [2011] EWCA Civ 246, KA v East Midlands Ambulance Service NHS [2015] EWHC 3930 (QB) and Bolitho v City and Hackney Health Authority [1998] AC 232, did not require proof of a precise mechanism. The claim therefore succeeded on causation.