pCO2 Gap (Central Venous-arterial Carbon Dioxide Difference) as A Guide to Adequacy of Fluid Resuscitation in Postoperative High Risk Surgical Patients and Prediction of Prognosis

BACKGROUND: pCO2 gap (ΔpCO(2)) calculated by the difference between central venous and arterial partial pressure of carbon dioxide has been evaluated as a global index of tissue perfusion. It has been used as a promising tool for adequacy of fluid resuscitation and marker of prognosis in critically ill. We hypothesized that pCO(2) gap could be used to identify patients still needing hemodynamic resuscitation in the immediate postoperative period following major abdominal surgery. PRIMARY OBJECTIVE: 1. To access the correlation of pCO(2) gap with adequacy of fluid resuscitation in postoperative high risk surgical patients. SECONDARY OBJECTIVES: 1. To compare pCO(2) gap with serum lactate levels, ScvO(2) (central venous oxygen saturation) levels. 2. To study the correlation of pCO(2) gap with 28-day mortality. MATERIAL AND METHODS: A prospective study was conducted on 60 postoperative high-risk adult surgical patients. 60 consecutive patients received in the ICU after major abdominal surgery who were on inotropic support and mechanical ventilation were included in the study. Demographic data, clinical characteristics, hemodynamic parameters, fluid intake, and inotropic doses were recorded on predesigned proforma. Arterial blood gas was done to evaluate pCO(2) gap, lactate and ScvO(2) at ICU admission, 12 hrs, and 24 hrs. Post-operative complications including postoperative sepsis (pneumonia, intraperitoneal abscess, wound infection, peritonitis and urinary tract infection), acute renal and cardiac failures, postoperative hemorrhage, ischemic events, and postoperative mortality were also recorded. Following univariate analysis, multivariate analysis using a logistic regression model was performed. RESULTS: In our study of 60 patients undergoing major abdominal surgery, mean pCO(2) gap in immediate post-operative period was higher in patients with complications than those without complications (7.8 ± 2 mm Hg vs. 5.6 ± 2). The higher number of patients who had persistently high pCO(2) gap at 24 hours even after fluid resuscitation belonged to the group with post-operative complications (n = 21, 34%) compared to the group of patients without complications (n = 9, 15%). Higher pCO(2) gap and higher sofa score were independently associated with postoperative complications. Higher pCO(2) gap was associated with increased incidence of organ failure, duration of mechanical ventilation, and length of stay. CONCLUSION: High pCO(2) gap (>6mm of Hg) can be used as a complementary tool to predictor of postoperative complications in high-risk patients following major abdominal surgery.