Predicting infection in localized intraabdominal fluid collections: Value of pH and pO(2) measurements

PURPOSE: To evaluate the use of pH, pO(2), and the subjective opinion of th e radiologist compared with bacterial culture in accurate diagnoses of bact erial infection in intraabdominal fluid collections. MATERIALS AND METHODS: Prospectively, 79 patients who were suspected of hav ing an intraabdominal fluid collection underwent diagnostic fluid aspiratio n. The aspirate was cultured and measured for pH and pO(2), A pH less than or equal to 7.1 and a pO(2) less than or equal to 49 mm Hg were threshold v alues used to separate infected from sterile fluid collections, RESULTS: pH alone had a 92% sensitivity and 79% specificity, whereas pO(2) aone had a 51% sensitivity and 79% specificity. pH or pO(2) combined yielde d a 92% sensitivity and 60% specificity. The radiologist's opinion produced a 83% sensitivity and 92% specificity. pH and the radiologist's opinion co mbined produced a 78% sensitivity and 96% specificity. pH or the radiologis t's opinion combined had a 95% sensitivity and a 63% specificity, CONCLUSION: pH is the most sensitive indicator of infection and the radiolo gist's opinion is the most specific, We recommend proceeding to drainage if the radiologist believes the collection to be infected and performing pH a nalysis if not. If the pH less than or equal to 7.04, proceed to drainage. If neither of the above criteria are met, drainage could be delayed, pendin g the results of culture.