Intraperitoneal xenon for the detection of early intestinal ischemia: Effect of ascites, adhesions, and misdirected injections

Significant delay in the washout of intraperitoneal xenon (¹³³Xe) in rats and dogs with decreased splanchnic blood flow (bowel strangulation, superior mesenteric artery and vein occlusion) has been previously demonstrated as the basis for radionucldide imaging to detect early (prenecrotic) intestinal ischemia. In this study, the effect of ascites, adhesions, and misdirected injections on the validity of this technique is evaluated. Xenon-133 (0.6 mCi) in 3 ml saline was injected into the peritoneal cavity of anesthetized rats and the washout of gamma activity monitored externally for 90 min. Gamma camera images were obtained at 30-min intervals. After 60 min, only 12 ± 2% of injected activity remained in the controls. Sham operation (13 ± 1%) and simple obstruction (12 ± 2%) had been previously shown not to significantly slow washout, but segmental strangulation had done so dramatically (32 ± 2%, P < 0.0001). In these experiments, ascitic fluid (Ringer's lactate) in volumes of 10 ml (13 ± 1%), 20 ml (13 ± 1%), and 40 ml (13 ± 1%), did not significantly slow washout in nonischemic rats. Sixty and eighty milliliters produced very tense ascites and slight but significant delay in washout (14 ± 1%, 17 ± 1%, respectively, P < 0.05). Moderate (11 ± 1%) and severe (11 ± 1%) adhesions produced by serosal scarification did not delay washout nor affect imaging. Injections of isotope intentionally misdirected into the abdominal wall (32 ± 2%), bowel wall (18 ± 1%), and bowel lumen (19 ± 2%), each significantly (P < 0.001) slowed washout. However, such misdirected injections were easily recognizable as such on the 1-min gamma camera images and could thereby be excluded as artifactual. Therefore, no false positive readings were obtained. It is concluded that the intraperitoneal xenon technique is not invalidated by mild to moderate ascites nor by moderate to severe adhesions. Misdirected injections produce invalid studies that are recognizable as such and thus are not misinterpreted. This approach should therefore be applicable to most patients with suspected intestinal ischemia.