Cerebrovascular relaxation responses to endothelium-dependent and -independent vasodilators after normothermic and hypothermic cardiopulmonary bypass in the rabbit.

BACKGROUND: Cardiopulmonary bypass causes activation of leukocytes and increased concentrations of proinflammatory mediators, which may result in endothelial dysfunction. Because hypothermia attenuates many inflammatory processes, the authors hypothesized that hypothermic cardiopulmonary bypass would be associated with better endothelial function than normothermic cardiopulmonary bypass. METHODS: Isoflurane-anesthetized New Zealand White rabbits were randomized to undergo 90 min of either normothermic (37 degrees C, n=9) or hypothermic (27 degrees C, n=9) cardiopulmonary bypass with terminal rewarming. A third group served as anesthetized normothermic non-cardiopulmonary bypass surgical controls (n=8). Basilar artery and descending thoracic aorta were isolated from each animal. In vitro vessel relaxation responses to increasing concentrations of acetylcholine (which induces endothelial release of nitric oxide) and nitroprusside (which provides exogenous nitric oxide) were measured in phenylephrine-precontracted vessel rings. RESULTS: There were no differences in vessel relaxation responses between normothermic and hypothermic cardiopulmonary bypass groups in basilar artery or aorta. In contrast, basilar arteries from non-cardiopulmonary bypass controls had increased relaxation responses to both acetylcholine (P=0.004) and nitroprusside (P=0.031) compared with the pooled cardiopulmonary bypass animal data. CONCLUSIONS: The authors observed no differences in endothelial or vascular smooth muscle function between normothermic and hypothermic cardiopulmonary bypass groups. Compared with non-cardiopulmonary bypass controls, cardiopulmonary bypass appeared to decrease basilar artery smooth muscle relaxation in response to endogenous and exogenous nitric oxide.

Recommendations for hyperbaric oxygen therapy of cerebral air embolism based on a mathematical model of bubble absorption.

Transcranial doppler studies show that microscopic cerebral artery air emboli (CAAE) are present in virtually all patients undergoing cardiac surgery. Massive cerebral arterial air embolism is rare. If it occurs, hyperbaric oxygen therapy (HBO) is recommended as soon as surgery is completed. We used a mathematical model to predict the absorption time of CAAE, assuming that the volumes of clinically relevant CAAE vary from 10(-7) to at least 10(-1) mL. Absorption times are predicted to be at least 40 h during oxygenation using breathing gas mixtures of fraction of inspired oxygen approximately equal to 40%. When CAAE are large enough to be detected by computerized tomography, absorption times are calculated to be at least 15 h. Decreases in cerebral blood flow caused by the CAAE would make the absorption even slower. Our analysis suggests that if the diagnosis of massive CAAE is suspected, computerized tomography should be performed, and consideration should be given to HBO therapy if the CAAE are large enough to be visualized, even if patient transfer to a HBO facility will require several hours.