Postoperative serum urea is associated with 30-day mortality in patients undergoing emergency abdominal surgery

BACKGROUND: Emergency abdominal surgery carries considerable postoperative morbidity and mortality. Hypovolaemia is considered to be a cause of renal hypoperfusion, which is associated with a decreased clearance of serum urea and creatinine. This study examines whether the perioperative serum urea and creatinine concentrations are predictors of mortality in patients undergoing emergency abdominal surgery. METHODS: Consecutive patients (n=300) who underwent emergency abdominal surgery were studied. Age- and sex-specific reference intervals were used for the data analysis. Patients with incomplete biochemical (n=51) or mortality data (n=31) or with pre-existing renal failure (n=9) were excluded from the analysis. RESULTS: 209 patients were analysed, of whom 162 (78%) remained alive and 47 (22%) died following surgery. The non-survivors were older (P<0.05), had undergone more extensive surgery (P<0.001) and were more likely to have been admitted to the intensive care unit (P<0.001). The serum urea concentration was higher preoperatively (P<0.05) and on day one postoperatively (P<0.001) in the non-survivors. On multivariate logistic regression analysis, age (odds ratio [OR] 3.27, 95% confidence interval [CI] 1.43-7.47, P<0.005), severity of surgery (OR 2.21, 95% CI 1.14-4.29, P<0.019), admission to intensive care (OR 0.54, 95% CI 0.11-0.54, P<0.001), seniority of anaesthetist (OR 0.50, 95% CI 0.27-0.90, P<0.022) and day one urea (OR 3.33, 95% CI 1.39-7.99, P<0.007) were independently associated with 30-day mortality. CONCLUSIONS: These results indicate that an increased serum urea concentration, but not serum creatinine concentration, in the postoperative period is associated with an increase in 30-day mortality in patients undergoing emergency abdominal surgery.