The purpose of this study was to evaluate the clinical relevance of high values of central venous-to-arterial carbon dioxide difference (PCO2 gap) in high risk surgical patients admitted in postoperative intensive care unit (ICU). We hypothesized that PCO2 gap could serve as a useful tool to identify patients still requiring hemodynamic optimization at ICU admission.
115 patients were included in this prospective single centre observational study during a one year period. High risk surgical inclusion criteria were adapted from Schoemaker et al. Demographic and biological data, PCO2 gap, ScvO2, lactate level and postoperative complications were recorded for all patients at ICU admission, 6 hours and 12 hours after admission.
A total of 78 (68%) patients developed postoperative complications whom 54 (47%) developed organ failure. From H0 to H12, there was a significant difference for mean PCO2 gap (8.7 ± 2.8 mmHg vs 5.1 ± 2.6 mmHg; p = 0.001) and median lactate values (1.54[1.1-3.2] mmol.l(-1) vs 1.06 ± [0.8-1.8] mmol.l(-1); p = 0.003) between patients who developed postoperative complications and those who did not. These differences were maximal at admission in ICU. At ICU admission, area under the receiver operating characteristic curve for occurrence of postoperative complications was 0.86 for the PCO2 gap compared to SOFA score (0.82), SAPS II score (0.67), lactate level (0.67). Threshold value for PCO2 gap was 5.8 mmHg. Multivariate analysis showed that only high PCO2 gap and a high SOFA score were independently associated with the occurrence of postoperative complications. A high PCO2 gap (≥6 mmHg) was associated to more organ failure, an increase in duration of mechanical ventilation and length of hospital stay.
A high PCO2 gap at admission in postoperative ICU was significantly associated with increased postoperative complications in high risk surgical patients. If the increase in PCO2 gap is secondary to tissue hypoperfusion then the PCO2 gap might be a useful tool complementary to ScvO2 as therapeutic target.