Abstracts
2000 Digestive Disease Week

# 2236 Predicting Conversion in Laparoscopic Colorectal Surgery: A Logistic Regression Model.
Tonia M. Young-Fadok, Heung W Lee, Charles H. Darby, Rochester, MN

AIM: Conversion from laparoscopic to open colorectal operation results in loss of patient benefits and increased costs. Our aim was to identify factors that predict conversion. METHOD: From 7/92-6/99, 315 laparoscopic colorectal procedures were performed; 69 were converted. Chart review identified factors potentially associated with conversion: age, gender, body mass index (BMI), prior operation, diagnosis, site of lesion, operative procedure, date of operation, and immunosuppressives. Variables were categorized on a-priori considerations. Univariate screening identified predictors significantly associated with conversion at the 0.25 level in order not to exclude potentially important predictors. Univariate logistic regression models investigated linear relationships between categorical variables and conversion; both linear and quadratic relationships were explored between continuous predictors and conversion. Interaction factors were sought. Stepwise selection was used to choose predictors to be included in the final prediction model. RESULTS: In the multivariate model, risk of conversion was significantly associated with BMI, age, diagnostic category (diverticular disease versus non-diverticular), and site of lesion (see Table). The final model was: ln(P/ (1-P)) = 0.06BMI + 0.03AGE + 0.88DIAG + 0.49SITE - 6.8996 where (P = risk of conversion). The c-value for this model was 0.71. The exponential of the resultant value X (i.e. ex) gives the odds ratio of conversion (P/(1-P)), and from this the risk of conversion, P, can be calculated. CONCLUSION: A logistic regression model was developed to predict risk of conversion. The risk is increased with increasing BMI and age, plus diverticulitis. This model will be employed clinically to guide operative approach and counsel patients.