Cerebral Blood Flow Response to Increases in Arterial CO 2 Tension during Alfentanil Anesthesia in the Rabbit

The stability of cerebral function and blood flow (CBF), and the CBF response to changes in arterial carbon dioxide tension (CBF reactivity) during alfentanil anesthesia were examined in rabbits. This model was first shown to provide stable anesthesia, cortical function, and CBF for 4 h. CBF increased significantly to 159% [of baseline] in the left hemisphere and to 167% in the right within 5 min of an exposure to 5% CO₂ (p = 0.009 on the left and p = 0.003 on the right), but then decreased to 123% on the left and to 137% on the right (not significantly different from baseline, p = 0.11 on the left and p = 0.07 on the right) while P_aCO₂ was still rising. Steady state reactivity levels (0.8 ml 100 g⁻¹/min⁻¹/mm Hg⁻¹ CO₂ on the left and 0.65 ml 100 g⁻¹/min⁻¹/mm Hg⁻¹ CO₂ on the right) were consistent with previous work and were reached at 20 min. These results suggest that mechanisms other than perivascular hydrogen ion concentration mediate the CBF response to changes in arterial CO₂ tension during alfentanil anesthesia.