In what will come as news to almost no one, researchers have found that “after hours” procedures, defined as those beginning after 4PM, are associated with higher rates of complications than procedures starting between 7AM-4PM, even after excluding emergency cases and controlling for patient and procedure conditions.

Time of day has already been shown to be a risk factor for complications during ICU care, dialysis, and anesthesia, so it is not surprising that the same applies to the operating room.

Interestingly, the effect was significant for morbidity but not for mortality, which we interpret as a sign that even the most fatigued resident will perk up after an unexpected cardiac arrest.

Although the researchers note that these results can only be extended to the VA system, from which the data were drawn, it’s reasonable to assume a similar problem occurs at most hospitals.

One potential criticism of these data is that the later cases typically involved much sicker patients. As the authors write:

Patients whose surgeries began after 4pm were more likely to have a history of heart failure, an impaired sensorium, a dependent functional status, and nutritional/immune compromise… The late group was also more likely to have renal or severe pulmonary compromise

Although, of course, the authors regressed out every such variable they could conceive of, it’s still possible that other factors went uncontrolled and confounded the observed effect.

It’s also possible that handing medical students the scalpel at 4pm is a bad idea after all.