Purpose: An erect chest radiograph for subdiaphragmatic free gas can be a useful adjunct in detecting a defect in gastrointestinal continuity. The usefulness of this test after laparotomy has not been defined, because the period of persistence of free gas is unknown. We set out to determine the length of time for natural absorption of postlaparotomy pneumoperitoneum in a prospective cohort study.
Method: Plain erect chest radiographs were performed on the second and fourth postoperative day and daily thereafter until the disappearance of subdiaphragmatic free gas after laparotomy.
Results: Seventy-five consecutive patients were studied after informed consent. The mean age was 62.1 (standard error of the mean, 1.7) years. On the fifth postoperative day, sixth postoperative day, and seventh postoperative day, 71.6, 80, and 89 percent of patients, respectively, had no visible subdiaphragmatic gas. Five patients had gas persisting beyond the tenth postoperative day. Two of these patients did not have an anastomosis. The use of drainage tubes did not affect significantly the mean time to disappearance of subdiaphragmatic free gas (4.5 vs. 4.9 days; P = 0.45: t-test). The duration of surgery, body mass index, and time to resume bowel function had no significant effect on gas disappearance. Two patients had a clinical leak on the fifth postoperative day. This was manifested as an increase in the collection of subdiaphragmatic gas during the course of a day.
Conclusion: By the sixth postoperative day 80 percent of patients had no subdiaphragmatic free gas on an erect chest radiograph regardless of the presence of a drainage tube. The erect chest radiograph may therefore be a simple and readily available adjunct in the evaluation of postoperative abdominal pain, especially after the sixth postoperative day when a similar prior examination is done routinely on the fourth postoperative day for comparison.