Gastric capnometry with air-automated tonometry predicts outcome in critically ill patients

Context: Contrary to tonometer gastric intramucosal pH, there is currently no validated threshold prognostic value for Pco(2) gap (tonometer gastric mucosal Pco(2) minus arterial Pco(2)) in the critically ill patient. Objective: To demonstrate a relationship between Pco(2) gap and mortality in mechanically ventilated patients. Design and Setting: Inception cohort study from a 9-month prospective survey of 95 consecutively ventilated critically ill patients in a teaching hospital. Patients: All the ventilated patients of the intensive care unit were included at their admission. Measurements and Main Results: Gastric Pco(2) using regional capnometry with air-automated tonometry, arterial gas, lactate, and organ system failure score were measured at admission and after 6, 12, 24, 48, 72, 96, and 120 hrs. For the entire population, the 28-day mortality was 44%. In multivariate analysis, independent predictors of death were organ system failure score (odds ratio, 2.12; 95% confidence interval, 1.02-3.14), 24-hr Pco(2) gap (odds ratio, 1.57; 95% confidence interval, 1.10-2.24), and 24-hr lactate (odds ratio, 1.48; 95% confidence interval, 1.06-2.05). We found a threshold value of 20 mm Hg for Pco(2) gap and 2.5 mmol/L for lactate, which was associated with a sensitivity of 0.70 and 0.72, respectively, and a specificity of 0.72 and 0.73, respectively. Conclusion: The Pco(2) gap is a marker of mortality in ventilated patients in the intensive care unit.