Central venous-to-arterial carbon dioxide difference as a prognostic tool in high-risk surgical patients

INTRODUCTION: The purpose of this study was to evaluate the clinical relevance of high values of central venous-to-arterial carbon dioxide difference (PCO(2) gap) in high-risk surgical patients admitted to a postoperative ICU. We hypothesized that PCO(2) gap could serve as a useful tool to identify patients still requiring hemodynamic optimization at ICU admission. METHODS: One hundred and fifteen patients were included in this prospective single-center observational study during a 1-year period. High-risk surgical inclusion criteria were adapted from Schoemaker and colleagues. Demographic and biological data, PCO(2) gap, central venous oxygen saturation, lactate level and postoperative complications were recorded for all patients at ICU admission, and 6 hours and 12 hours after admission. RESULTS: A total of 78 (68%) patients developed postoperative complications, of whom 54 (47%) developed organ failure. From admission to 12 hours after admission, there was a significant difference in mean PCO(2) gap (8.7 ± 2.8 mmHg versus 5.1 ± 2.6 mmHg; P = 0.001) and median lactate values (1.54 (1.1-3.2) mmol/l versus 1.06 (0.8-1.8) mmol/l; P = 0.003) between patients who developed postoperative complications and those who did not. These differences were maximal at admission to the ICU. At ICU admission, the area under the receiver operating characteristic curve for occurrence of postoperative complications was 0.86 for the PCO(2) gap compared to Sequential Organ Failure Assessment score (0.82), Simplified Acute Physiology Score II score (0.67), and lactate level (0.67). The threshold value for PCO(2) gap was 5.8 mmHg. Multivariate analysis showed that only a high PCO(2) gap and a high Sequential Organ Failure Assessment score were independently associated with the occurrence of postoperative complications. A high PCO(2) gap (≥6 mmHg) was associated with more organ failure, an increase in duration of mechanical ventilation and length of hospital stay. CONCLUSION: A high PCO(2) gap at admission in the postoperative ICU was significantly associated with increased postoperative complications in high-risk surgical patients. If the increase in PCO(2) gap is secondary to tissue hypoperfusion then the PCO(2) gap might be a useful tool complementary to central venous oxygen saturation as a therapeutic target.