Analysis of pH and pO2 in abscesses, peritoneal fluid, and drainage fluid in the presence or absence of bacterial infection during and after abdominal surgery.

The diagnostic significance of pH, pO2 (partial pressure of oxygen), and pCO2 (partial pressure of carbon dioxide) was studied in pus, peritoneal fluid, and drainage fluid obtained during or after abdominal surgery. Measurements of these fluids in 59 patients with clinically and bacteriologically documented abdominal or anorectal infection (median pH: 6.75, median pO2: 28 mm Hg, median pCO2: 89 mm Hg) differed significantly (p < 0.001) from data of 105 patients undergoing elective laparotomy for a reason other than infection (median pH: 7.49, median pO2: 144 mm Hg, median pCO2: 92 mm Hg). The combined use of a threshold criterion for pH and pO2 allowed for excellent discrimination between infected (pH less than 7.1, pO2 less than 49 mm Hg) and noninfected patients, with positive and negative predictive values of 98% and 99%, respectively. In conclusion, conditions prevailing during standard in vitro susceptibility tests more closely reflect physiologic conditions as opposed to the conditions prevailing at the site of abdominal infections. Measurements of pH and pO2 allow for an easy, quick, sensitive, and specific diagnosis of bacterial abdominal infection.