Venous-arterial PCO2 and pH gradients in acutely ill postsurgical patients.

OBJECTIVE: To investigate the venous-arterial PCO2 gradient, and the mixed venous blood acid-base status together with the oxygen transport variables in a group of acutely ill postsurgical patients. DESIGN: Retrospective, descriptive study of hemodynamic and acid-base data collected immediately after the patients' admission to the Postsurgical Intensive Care Unit. SETTING: Eight-bed, Postsurgical Intensive Care Unit in a University Hospital. PATIENTS: A total of one hundred and one postsurgical patients (87 male, 14 female; 14 to 86 years). INTERVENTIONS: None immediately before the first measurement. MEASUREMENTS AND MAIN RESULTS: Hemodynamic, oxygen transport variables, and arterial and mixed venous acid-base status measurements obtained immediately after the admission to the Postsurgical Intensive Care Unit. The venous-arterial PCO2 gradient was elevated (> 6 torr) in 23 patients and normal (< or = 6 torr) in 78 patients (respectively 9.1 +/- 3.3 vs 4.4 +/- 1.0 torr, p < 0.001). Patients with an increased venous-arterial PCO2 gradient had a higher arterial-venous pH gradient (0.05 +/- 0.03 vs 0.03 +/- 0.01 Unit, p < 0.001) and mixed venous PCO2 (47.5 +/- 8.0 vs 42.1 +/- 5.6 torr, p < 0.001). These patients had a lower cardiac index, oxygen delivery, mixed venous oxygen saturation, and a higher oxygen extraction index than the patients with normal venous-arterial PCO2 and pH gradients. For all the measurements, there was an inverse non linear significant relation between oxygen delivery, venous-arterial PCO2 (r = 0.74, p < 0.001) and pH (r = 0.57, p < 0.01) gradients. CONCLUSIONS: This study suggests that in acutely ill postoperative patients increased venous-arterial PCO2 and pH gradients are directly and principally related to the reduction in blood flow and are both suggestive of low-flow state.