Q: The rule at our ambulatory surgery unit (ASU) is that a patient who received sedation should not drive after discharge. They are instructed about this when they make their appointment and on the day of the procedure. Recently, a patient I did anesthesia on left on his own and there was a problem. When he didn’t answer his phone, the head nurse sent the cops to his house, and he was passed out on the porch. EMS brought him to the ER, and he was fine. Risk management has told me that I have no issue here, because this all occurred after I signed him out to recovery, but I’m not clear on how the hospital could be on the hook if he had had a bad outcome since he broke the rule.

You are referring to the legal doctrine of intervening superseding cause, which goes back to the requirement that when a plaintiff is making a medical malpractice claim, they must show that the alleged negligent act or omission was the proximate cause of the harm that they suffered —that it was the direct and uninterrupted cause of the injury. If there are several negligent acts in the series of events that resulted in an injury, a subsequent act by another defendant or by the plaintiff themselves may sever the causal link to the original defendant for some or all of the ultimate injury.

This would then be an “intervening superseding cause” of the injury—“intervening” because it happened between the original negligence and the injury, impinging on the connection between them, and “superseding” because it turned aside the original course to a different outcome. The intervening superseding cause doctrine will apply if the subsequent negligent act or omission was 1) sufficient by itself to cause the injury and 2) was not foreseeable to the first defendant.

A defendant is not responsible to predict a rare event but cannot claim that anything less than certainty was not foreseeable. The exact mechanism of subsequent negligence does not have to be foreseeable if the general mechanism is foreseeable.

In the situation at your ASU, the patient’s choice to leave and drive despite being made aware of the safety issues was definitely negligent. It also was capable of causing the harm on its own. However, that someone might leave and drive despite the rule was fully foreseeable. The patient’s conduct, therefore, did not interrupt the causation from the hospital’s negligence in failing to keep an adequate eye on patients who should not leave and drive.