Cerebral metabolism and the electroencephalogram during hypocapnia plus hypotension induced by sodium nitroprusside or trimethaphan in dogs

The effects on cerebral metabolism and the electroencephalogram (EEG) of combining hypocapnia with hypotension have been only incompletely examined. The present study examined the possibility that hypocapnia may worsen the cerebral metabolic and EEG disturbances caused by hypotension. Cerebral metabolism and the EEG were studied at three levels of hypotension during hypocapnia (PaCO2 = 20 mm Hg) in dogs under light halothane anesthesia. A sequential decrease of the mean arterial pressure (MAP) to 60, 50, and 40 mm Hg (30 minutes at each level) was achieved with sodium nitroprusside (SNP) (n = 12) or trimethaphan (TMP) (n = 12). With SNP-induced hypotension plus hypocapnia, the power of the alpha and beta 2 spectra of the EEG decreased at MAP less than or equal to 60 mm Hg. Cerebral metabolic values were unchanged at a MAP of 60 or 50 mm Hg. Brain tissue phosphocreatine and the cerebral energy charge decreased, and the lactate/pyruvate ratio increased at a MAP of 40 mm Hg. With TMP-induced hypotension plus hypocapnia, power decreased in the alpha and beta 2 spectra of the EEG at MAP less than or equal to 60 mm Hg. Cerebral metabolic values were unchanged at a MAP of 60 mm Hg. At MAP less than or equal to 50 mm Hg, power in the beta 1 spectrum, brain tissue phosphocreatine, and the cerebral energy charge all decreased. At a MAP of 40 mm Hg, the cerebral glucose value decreased and the lactate/pyruvate ratio increased.(ABSTRACT TRUNCATED AT 250 WORDS)