We identified several other patient characteristics that were associated with perioperative complications. Our data were consistent with previous studies linking a history of congestive heart failure,6,7,27,28 significant tobacco use,3,5,29 dementia,5,30 Parkinson disease,31,32 and higher ASA classification4,5,9- 11,22 to increased operative risk. Interestingly, in our study group, age was not an independent predictor of surgical risk. While at least one other study has shown similar findings,33 most other studies have shown age to be an important factor.4,5,7,8,27,28 Several characteristics related to the surgical procedure were also associated with higher risk. Our data confirmed prior reports showing patients with thoracic or peritoneal procedures3,7 to be at increased risk for complications. As in previous studies,3- 5 perioperative complications were associated with prolonged duration of anesthesia. In our data, this was particularly striking when the duration of anesthesia was 8 hours or more. This may be caused by the physiologic stress of the anesthesia, blood loss, or hypothermia,34 or it may simply reflect the complexity and severity of the procedure (eg, number of tissue planes crossed and number of services involved).