Postoperative free intraperitoneal gas
Postoperative free intraperitoneal gas refers to the presence of gas in the peritoneal cavity following a surgical procedure and may result from open or laparoscopic surgical techniques.
Terminology
Postoperative free intraperitoneal gas is also referred to as postoperative pneumoperitoneum .
Epidemiology
Free intraperitoneal air after surgery occurs in up to 60% of laparotomies and 25% of laparoscopic procedures . Larger volumes of gas are associated with a smaller body mass index .
Clinical presentation
A tympanic percussion sound on percussion may be elicited on abdominal examination. Post laparoscopic shoulder pain is a common complication following laparoscopic surgery and is caused by irritation of the phrenic nerve by the retained gas used during laparoscopy .
Pathology
In open surgical procedures, direct incision of the skin and then closure of the incision traps gas within the peritoneal cavity. In laparoscopic procedures, insufflation of the peritoneum introduces gas (usually carbon dioxide) which is then retained. The gas is gradually reabsorbed by surrounding tissue and blood vessels and is then expired via the lungs.
In one study the volume of postoperative intraperitoneal gas in a group of patients who underwent laparoscopic gynecological surgery was an average of 17 mL but measured as much as 130 mL in some patients .
Radiographic features
Plain radiograph
Signs of pneumoperitoneum such as subdiaphragmatic free air and the cupola sign may be visible on chest radiographs. The volume of gas on serial radiographs should decrease. If the volume of gas increases then it is concerning for another cause of pneumoperitoneum following surgery such as bowel perforation or anastomotic leak.
On abdominal radiographs, signs of pneumoperitoneum may be visible (eg. Rigler sign).
Treatment and prognosis
If there are no features of peritonitis or other concerning features, management is conservative and the gas will gradually be reabsorbed . Two-thirds of cases resolve within 48 hours and 97% resolve within 5 days . However, whilst the free gas may be considered as an expected postoperative finding if the clinical features point to intra-abdominal deterioration, further imaging such as CT should be considered.
The volume of postoperative free gas is positively associated with the intensity of postoperative pain .
Differential diagnosis
