Incidence and significance of pneumoperitoneum in continuous ambulatory peritoneal dialysis

In a retrospective study we reviewed upright chest x-ray films of 101 continuous ambulatory peritoneal dialysis (CAPD) patients to determine the incidence and significance of free subdiaphragmal air. A pneumoperitoneum (PP) was diagnosed if a minimal shadow of free air was detected under the diaphragm. The amount of free air was determined by measuring the height and width of the subdiaphragmal air shadow. Of all CAPD patients, 33.6% (34 of 101) had at least one occurrence of PP. Thirteen of these 34 patients (38.2%) were diagnosed within 30 days after catheter implantation, 10 patients (29.5%) acquired a PP during an episode of peritonitis, and in 11 patients (32.4%) no additional risk factor could be determined. Patients radiographed within 30 days after catheter implantation showed a statistically significant higher incidence of PP compared with the same patients radiographed later (22% v 10%; P < 0.05). The incidence of PP in CAPD patients suffering from peritonitis (33%) was significantly higher than in patients without peritonitis (10%; P < 0.001). The amount of free air did not differ statistically significantly between the investigated groups. Only two patients with PP and peritonitis had surgically confirmed visceral perforation. Therefore, the main reason for PP seemed to be handling faults during CAPD bag exchange. There was no correlation between the organisms causing peritonitis and PP or the CAPD connector system and PP. In conclusion, a PP occurs in approximately one third of all CAPD patients and a visceral perforation cannot be diagnosed by the occurrence and amount of free subdiaphragmal air.