The zero mortality paradox in surgery

Patients considering where to have surgery may reasonably believe that their chances of survival are highest at hospitals whose reported operative mortality is zero. We sought to determine if hospitals with zero mortality over 3 years also have lower than average mortality in the subsequent year.

We obtained national Medicare data on five operations with high operative mortality (> 4.0%): coronary artery bypass grafting, abdominal aortic aneurysm repair, and resections for colon, lung, and pancreatic cancer. For each procedure, we defined zero mortality hospitals as those with no inpatient or 30-day deaths during the 3-year period 1997 to 1999. To determine whether these hospitals actually have lower mortality than other hospitals, we compared their mortality during the next year (2000) with the mortality at all other hospitals.

For four procedures, operative mortality in zero mortality hospitals in the subsequent year was no different than that in other hospitals: abdominal aortic aneurysm repair (6.3% zero mortality hospitals versus 5.8% other hospitals; (adjusted relative risk [RR]=1.09; 95% CI 0.92 to 1.29); lobectomy for lung cancer (5.1% versus 5.3%; RR=0.96; 95% CI 0.80 to 1.15); colon cancer resection (6.0% versus 6.6%; RR=0.91; 95% CI 0.80 to 1.03); and coronary artery bypass surgery (4.0% versus 5.0%; RR=0.81; 95% CI 0.61 to 1.04). In the case of pancreatic cancer resection, zero mortality hospitals had substantially higher mortality than other hospitals (11.2% versus 8.7%; RR=1.29; 95% CI 1.04 to 1.59).

Paradoxically, hospitals with a history of zero mortality subsequently experience mortality rates that are the same or higher than those of other hospitals. Patients considering surgery should not consider a reported mortality of zero as being a reliable indicator of future performance.