Background and Goal of Study
The PCO2 gap (ΔPCO2) is considered as a marker of the ability of the venous blood flow to remove the CO2 excess produced in tissues. Some studies have shown that the venous-to-arterial carbon dioxide difference might be a useful and complementary tool to detect persistent tissue hypoperfusion during major abdominal and vascular surgery. However, usefulness of the PCO2 gap during laparoscopic operations have not been studied. 
Materials and Methods
38 ASA III patients with curable colorectal cancer undergoing open (n = 15, group №1) or laparoscopic (n = 23, group №2) elective colorectal surgery.  Arterial and central venous blood gas analyses and noninvasive monitoring of hemodynamic were performed before induction, after induction before pneumoperitoneum or incision, after 10 min, 30 min, 1 h and 2 h of pneumoperitoneum or start of operation, after desuflation or the end of operation. Pneumoperitoneum maintained at the 11-12 mm H2O. Mechanical ventilation maintained normocapnia in the both groups. 
Results and Discussion
Demographic and biological data were comparable between two groups. ΔPCO2 before surgery was 4.8±2.3 mmHg in the group №1 and 5.1±2.2 mmHg (p = 0.75, Mann-Whitney U tests) and cardiac index was 3.1±0.4 and 3.2±0.5 l/min/m2, respectively. During anesthesia venous-to-arterial carbon dioxide difference was significantly higher in the group №2 at all time points (4.2±1.6 vs 5.7±2.2 mmHg, 4.5±1.8 vs 6.5±2.1 mmHg, 4.4±0.9 vs 7.3±2.8 mmHg, 4.7±2.0 vs 7.4±2.9 mmHg at the 10 min, 30 min, 1 h and 2 h for group №1 and №2, respectively, p < 0.05, Mann-Whitney U tests). In the group №2 we distinguished people with decreased cardiac index during pneumoperitoneum (subgroup A, n = 8, mean cardiac index 2.1±0.25 l/min/m2), and carbon dioxide difference was significantly higher after 30 min, 1 h and 2 h in comparison with people with preserved cardiac index from the group №2 and people from the group №1 (7.2±1.9 vs 5.9±1.9 vs 4.5±1.8 mmHg, 8.2±2.1 vs 6.4±1.3 vs 4.4±0.9 mmHg, 8,2±2.6 vs. 6.6±2.9 vs 4.7±2.0 mmHg at the 30 min, 1 h and 2 h for the group №2A, №2, №1, respectively, p < 0.05, Mann-Whitney U tests)  ROC analyses have shown sensitivity 57,1% and specificity 81,2% for the cutoff value 8 mmHg for decreased cardiac index during laparoscopy. 
Conclusion. We speculate that ΔPCO2 may be a marker of hypoperfusion due to insufficient cardiac output during elective laparoscopic operation. Further studies need to confirm our hypothesis. 


06 / Central venous-to-arterial carbon dioxide gradient usefullness during laparoscopic operations