Intracranial pressure during nitroglycerin-induced hypotension

Nitroglycerin was given intravenously to 5 anesthetized, hyperventilated (PaCO₂ 25 to 30 torr) patients during craniotomy, to facilitate surgery by creating a relatively bloodless field, and to decrease the potential need for blood transfusion. A subarachnoid screw and an indwelling radial artery catheter were inserted to monitor intracranial pressure (ICP) and mean arterial pressure (MAP). As MAP decreased from 104.4 ± 4.0 (SE) to 69.0 ± 1.8 torr, ICP increased from 14.2 ± 0.7 (SEM) to 30.8 ± 1.1 torr. Cerebral perfusion pressure decreased from 90.2 ± 3.6 (SEM) to 38.2 ± 2.3 torr (p < 0.0005). The authors attribute this nitroglycerin-induced ICP increase to capacitance vessel dilation within the relatively noncompliant cranial cavity, with subsequent cerebral blood volume increase.