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

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.

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.

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.

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.