Effects of increasing FiO₂ on venous saturation during cardiopulmonary bypass in the swine model

Adequacy of perfusion during cardiopulmonary bypass (CPB) is dependent on nutrient delivery and waste removal from the tissue. A recent study showed that over 75% of cardiopulmonary bypass procedures are completed using continuous venous saturation (SvO₂) monitoring. The purpose of this study was to determine the effect of changing FiO₂ concentration on SvO₂. A total of eight mixed gender 45-kg swine were placed on CPB under moderate hypothermic conditions. Animals were divided evenly into two groups: Experimental, where FiO₂ was increased to 100% and blood flow decreased to an SvO₂ level of prechange in FiO₂, and Control, where the same condition was created except no change in blood flow. Variables measured include hemodynamic, blood gas, intramyocardial pH, and lactic acid concentrations. In the experimental group, percentage change of blood flow was decreased from baseline 28.4% ± 12.5% (p < .005) as well as percentage change of oxygen delivery 23.9% ± 14.7% (p < .005). Systemic venous saturation percentage change was increased in both the experimental 14.4% ± 6.8% (p < .05) and control 11.2% ± 7.1% (p < .05) groups. Jugular venous saturation percentage change was decreased in the experimental group 7.8% ± 6.34% (p < .02), but not in the control animals. Myocardial venous saturation percentage change decreased in the experimental group to 3.73% ± 8.34% (p < .004). Experimental manipulation, however, did not significantly change jugular lactic acid concentrations or intramyocardial pH values. In conclusion, these results suggest that decreased blood flow adjusting for increased SvO₂ associated with high PaO₂ did not result in significant reduction of adequacy of perfusion markers for organs studied.