Prolonged surgery increases the likelihood of admission of scheduled ambulatory surgery patients

Study Objective: To identify variables influencing the likelihood of unanticipated admission following scheduled ambulatory surgery. Design: Retrospective case-controlled chart review study. Setting: A large academic tertiary care hospital. Patients: 8,549 ASA physical status I, II, III, and IV patients who underwent scheduled ambulatory surgery in 1991. Measurements and Main Results: Of the 8,549 patients, 216 were admitted, with complete medical record information available for 167 of the admitted patients. The most common reasons for admission among the 167 were surgical (43%), anesthetic (28%), and medical (17%) complications. Odds for admission following long surgery (of at least 60 minutes) were 7.5 times (p < 0.001) greater than following short surgery (under 60 minutes). Among long cases, independent variables influencing admission were: general anesthesia [odds ratio 20.8; 95% confidence interval (CI) 4.4 to 45.6], and monitored anesthesia care or regional anesthesia (combined odds ratio 8.3; 95% CI 1.7 to 40.8). ASA physical status and patient age did not significantly influence admission rate for long cases. For short cases, patients over 65 years (odds ratio 5.6; 95% CI 2.6 to 12.0), ASA physical status III or IV (odds ratio 4.8; 95% CI 2.0 to 11.6), use of general anesthesia (odds ratio 4.7; 95% CI 1.5 to 14.2), and monitored anesthesia care or regional anesthesia (odds ratio 3.1; 95% CI 1.0 to 10.1) independently influenced the likelihood of admission. Type of surgery and gender had no detectable effect on admission. Conclusions: Surgery duration of 60 minutes or longer was the most important predictor of unanticipated admission following scheduled ambulatory surgery.