The Effect of PaCO₂ on Cerebral Perfusion: An Experimental Swine Model

Abstract

Adequate cerebral perfusion is of particular concern to the clinician and is a major factor in postoperative morbidity. Cerebral circulation has the ability to autoregulate blood flow in order to maintain nutrient delivery and prevent high intravascular pressures. The focus of this study was to characterize the impact of gradually changing arterial CO2 levels on cerebral perfusion. A total of eight porcine subjects were placed into either a normothermic group (NG, N = 4, rectal temperature = 35.4 ± 1.2° C) or a hypothermic group (HG, N = 4, 30.6 ± 0.6° C). After initiation of cardiopulmonary bypass, the PaCO2 values sequentially varied between 24 and 56 mmHg. Arterial, venous, and internal jugular blood gas data were collected at 4 mmHg increments, and relative cerebral blood flow was calculated as CBF = 1 (CarterialO2–CjugularO2)−1 Physiological parameters were similar in both groups across all test conditions: mean arterial pressure— NG 81.6 ± 11.9 mmHg versus HG 73.4 ± 7.0 mmHg, p = NS, and systemic oxygen consumption—HG 110.6 ± 30.0 mL min−1 versus NG 136.4 ± 37.9 mL min−1, p = NS. No significant differences were found in CBF in the NG (21.8 ± 4.4 mL min−1 100 gL at PaCO2= 56 mmHg versus 20.5 ± 5.0 mL min−1 100 g−1 at PaCO2 = 24 mmHg) or the HG (24.3 ± 9.5 mL min−1 100 g−1 at PaCO2 = 56 mmHg versus 25.6 ± 12.0 mL min−1 100 g−1 at PaCO2 = 24 mmHg). In conclusion, the alteration of PaCO2 under both hypothermic and normothermic conditions resulted in no significant differences in 1 (CarterialO2 – CjugularO2)−1 in this model.