The interaction of nitrous oxide and isoflurane with incomplete cerebral ischemia in the rat

In rats with incomplete cerebral ischemia the effects of 70% N2O alone, isoflurane alone (0.5 and 1 MAC), and the combination of N2O + isoflurane on neurologic outcome, neurohistopathology, and EEG were compared. Moderate and severe ischemia were produced by right carotid artery occlusion combined with hemorrhagic hypotension (moderate ischemia, MAP = 30 mmHg, FIO2 = 0.30; severe ischemia, MAP = 25 mmHg, FIO2 = 0.20). Neurologic outcome was evaluated using a graded deficit score from 0 to 5 (0 = normal, 5 = death associated with stroke), and neurohistopathology was evaluated using a 40-point scale from 0 = normal to 40 = total hemisphere infarct at the level of the caudate nucleus in coronal section. Compared with N2O alone, isoflurane (0.5 and 1 MAC) improved neurologic outcome following moderate ischemia (P less than 0.05). Isoflurane also decreased histopathologic damage following moderate ischemia (N2O control = 33 +/- 1 vs. 0.5 MAC isoflurane = 11 +/- 4 and 1 MAC isoflurane = 12 +/- 3, P less than 0.05), whereas only 0.5 MAC isoflurane decreased histopathologic damage following severe ischemia (N2O control = 38 +/- 1 vs. 0.5 MAC isoflurane = 25 +/- 5; P less than 0.05) Adding N2O to 0.5 MAC isoflurane attenuated the neurologic protective effect of isoflurane alone and increased histopathologic damage following both moderate and severe ischemia (moderate = 23 +/- 5, severe = 37 +/- 2; both P greater than 0.05 compared with N2O controls). The effect of adding 70% N2O to isoflurane on cerebral blood flow (CBF) and cerebral oxygen consumption(CMRO2) was also evaluated.(ABSTRACT TRUNCATED AT 250 WORDS)