Subanesthetic concentration of sevoflurane increases regional cerebral blood flow more, but regional cerebral blood volume less, than subanesthetic concentration of isoflurane in human volunteers

Both sevoflurane and isoflurane are used in moderate concentrations in neur oanesthesia practice. The limiting factors for using higher concentrations of inhalational anesthetics in patients undergoing neurosurgery a e e agent s' effects on cerebral blood flow (CBF) and cerebral blood volume (CBV). In particular, an increase in CBV, which is a key determinant of intracranial pressure, may add to the neurosurgical patient's perioperative risk. To co mpare the effects of a subanesthetic concentration (0.4 minimum alveolar co ncentration) of sevoflurane or isoflurane on regional CBF (rCBF), regional CBV (rCBV) and regional mean transit time (rMTT), contrast-enhanced magneti c resonance imaging perfusion measurements were made in spontaneously breat hing human volunteers. Absolute changes in rCBF, regional CBV, and rMTT dur ing administration of either drug in regions of interest outlined bilateral ly in white and grey matter were nonparametrically (Mann-Whitney test) anal yzed. Sevoflurane increased rCBF in practically all regions (absolute chang e, 4.44 +/- 2.87 to 61.54 +/- 2.39 mL/100g per minute) more than isoflurane did (absolute change, 12.91 +/- 2.52 to 52.67 +/- 3.32 mL/100g per minute) , which decreased frontal, parietal, and white matter rCBF (absolute change , -1.12 +/- 0.59 to -14.69 +/- 3.03 mL/100g per minute). Regional CBV was h igher in most regions during isoflurane administration (absolute change, 0. 75 +/- 0.03 to 4.92 +/- 0.16 mL/100g) than during sevoflurane administratio n (absolute change, 0.05 +/- 0.14 to 3.57 +/- 0.14 mL/100g). Regional mean transit time was decreased by sevoflurane (absolute change, -0.18 +/- 0.05 to -0.60 +/- 0.04 s) but increased by isoflurane (absolute change, 0.19 +/- 0.03 to 0.69 0.04 s). In summary, regional CBV was significantly lower dur ing sevoflurane than during isoflurane administration, although sevoflurane increased rCBF more than isoflurane, which even decreased rCBF in some reg ions. For sevoflurane and, even more pronouncedly, for isoflurane, the obse rved changes in cerebral hemodynamics cannot be explained by vasodilatation alone.