MANIPULATION OF CEREBROVASCULAR RESISTANCE DURING INTERNAL CAROTID-ARTERY OCCLUSION BY INTRAARTERIAL VERAPAMIL

Occlusion of the internal carotid artery (ICA) results in acute cerebr al hypotension. We hypothesized that during acute cerebral hypotension , in addition to physiological autoregulation, further arteriolar rela xation is possible by pharmacological means. We tested the feasibility of using intracarotid verapamil, a calcium channel blocker, to decrea se the cerebrovascular resistance (CVR) and augment cerebral blood flo w (CBF) at low postocclusion distal ICA pressures (P-ICA). Eleven pati ents undergoing trial occlusion of ICA were enrolled. Distal ICA or st ump pressure, hemispheric CBF, and CVR were determined before and afte r carotid occlusion. During ICA occlusion, CBF and other physiological variables were determined before and after intracarotid verapamil. Tw o patients were excluded from the study. Carotid occlusion (n = 9) sig nificantly decreased P-ICA (mean +/- SD, from 82 +/- 22 to 46 +/- 11 m m Hg, P = 0.001) and CBF (from 42 +/- 11 to 33 +/- 11 mL.100 g(-1).min (-1), P < 0.05). During occlusion, after intracarotid verapamil (3.9 /- 1.6 mg), hemispheric CBF tended to increase from 31 +/- 11 to 35 +/ - 14 mL.100 g(-1).min(-1) (P = 0.067). However, the percent increase i n CBF after verapamil was a linear function of P-ICA (y = 1.01 x -32, n = 9, r(2) = 0.84, P = 0.006). The decrease in CBF during carotid occ lusion suggests that near maximal cerebral autoregulatory vasodilation had occurred, although our results indicate that it may be feasible t o further augment CBF by pharmacological means during acute cerebral h ypotension. Implications: When the internal carotic artery is occluded during neurosurgical procedures, there may be a significant reduction in cerebral perfusion. The authors have demonstrated that the intraar terial administration of verapamil increases cerebral blood flow as a linear function of cerebral artery pressure. Intracarotid injection of vasodilators may augment cerebral blood flow during acute cerebral hy potension.