Integrity of the Cerebral Blood-Flow Response to Hyperoxia After Cardiopulmonary Bypass

Objective: In this study, the hypothesis that cardiopulmonary bypass (CPB) alters the cerebral blood flow (CBF) vasoconstrictive response to hyperoxia was tested. Design: A prospective, observational study was conducted. Setting: The study was conducted at a single university hospital. Participants: Subjects were patients who presented for cardiac surgery with CPB. Interventions: CBF was measured before and after CPB in 12 subjects while breathing 21% O₂ and 100% O₂. CBF was measured by using continuous arterial spin labeling (CASL) perfusion magnetic resonance imaging. Arterial pO₂ (mmHg), pCO₂ (mmHg), hemoglobin (Hgb), and oxygen content (CaO₂) were also measured. Measurements and Main Results: Mean age of the 12 subjects was 63 ± 16 years. Hgb decreased from 12.0 (±2.4) g/dL to 9.2 (±2.9) g/dL postoperatively (p = 0.008). CBF increased by 39%, from 37.2 (±10.8) mL/100 g/min to 49.2 (±14.3)mL/100 g/min postoperatively (p = 0.01). In response to the hyperoxic challenge CBF decreased by 8.0 (±7.1) mL/100 g/min (21%) preoperatively and by 9.4 (±6.4) mL/100 g/min (19%) postoperatively (p = 0.58). By using multiple regression, the contribution of CPB to the hyperoxic CBF response (ΔCBF) was evaluated, while controlling for other potentially important covariates known to influence CBF, including age, baseline CBF on 21% O₂, and changes in arterial pO₂, pCO₂, and CaO₂. CPB state was not found to be a significant covariate in controlling the CBF response to hyperoxia. Conclusions: CPB does not impair the CBF response to hyperoxia.