Postoperative pneumoperitoneum as detected by CT: prevalence, duration, and relevant factors affecting its possible significance.

BACKGROUND: To determine the prevalence and duration of postoperative pneumoperitoneum as detected on computed tomography (CT) and to evaluate factors that influence postoperative pneumoperitoneum.

METHODS: One hundred three CT examinations of 89 patients performed after abdominal surgery for various indications were prospectively collected and reviewed. The presence and volume of free air were noted and correlated with patients' sex, age, and habitus, with the time interval between surgery and CT, with the type of surgery, and with the presence of drains.

RESULTS: Pneumoperitoneum was seen in 44% of examinations performed in the first 3 days after surgery and in 30% between the 4th and 18th postoperative days. The prevalence and volume of free air decreased with the time interval between surgery and CT. It was not detected in any of the 11 examinations performed beyond the 18th postoperative day. The volume of free air in the majority of examinations did not exceed 10 mL and ranged from 0.2 to 10 mL in 19 patients (66% of patients with free air). Larger volumes of free air, ranging from 10 to 20 mL and from 20 to 40 mL, were observed in 5 (17%) and 4 (14%) patients, respectively, and only one patient had more than 40 mL of free air. Free air was found significantly more often in male and in asthenic patients; age had no significant effect. Free air was more prevalent in the presence of drains. The type of surgery did not significantly influence the prevalence of postoperative pneumoperitoneum, although it was noted slightly less often after laparoscopic surgery than after open laparotomy.

CONCLUSIONS: Pneumoperitoneum is a common phenomenon after abdominal surgery, decreasing in frequency with time. The air is most often residual and not a sign of disruption of the gastrointestinal tract. Obesity, female sex, and occurrence of free air several weeks after surgery are factors suggestive of a leak, but the significance of a postoperative pneumoperitoneum on CT should be determined mainly by the clinical setting.