Carbon dioxide reactivity and local cerebral blood flow during prostaglandin E1- or nitroglycerin-induced hypotension

The aims of this randomized study were to determine the effect of prostaglandin-(PGE1) or nitroglycerin-(TNG) induced hypotension on local cerebral blood flow (LCBF) and carbon dioxide reactivity during isoflurane anaesthesia in 20 patients after subarachnoid haemorrhage (SAH) scheduled for aneurysm clip ligation. Mean arterial blood pressure decreased immediately, after giving either PGE1 or TNG. The LCBF, measured using a thermal gradient blood flowmeter, was unchanged after PGE1, while the LCBF increased after TNG infusion (control; 47.6 + 10.0, 60 min after infusion; 55.1 +/- 6.5 (P < 0.05), before clipping; 55.5 +/- 7.8 (P < 0.05)) but returned to control values after its discontinuation. Carbon dioxide reactivity, calculated from % delta LCBF/delta PaCO2 was unchanged during PGE1- or TNG-induced hypotension (PGE1; 2.13 +/- 0.9, 2.48 +/- 0.68 and 2.31 +/- 0.79%/mmHg for before, during and after hypotension respectively) (TNG; 2.08 +/- 0.68, 2.17 +/- 0.64 and 2.02 +/- 0.69%/mmHg for before, during and after hypotension respectively). Carbon dioxide reactivity correlated with presurgical neurological status (rs = -0.7, -0.648 and -0.458 for before, during and after hypotension respectively) and the initial LCBF (rs = -0.605). These results suggest that both PGE1 and TNG are useful drugs for induced hypotension for cerebral aneurysm surgery, because neither decreased LCBF.