The effects of surgical stimulation on intracranial hemodynamics

This study investigates the effects of surgical stimulation on cerebral blood flow velocity using transcranial Doppler sonography (TCD) in 1 and 2 maximum alveolar concentration (MAC) isoflurane anesthetized patients. Sixty ASA I and II patients undergoing breast surgery were studied. Anesthesia was maintained with 0.6% isoflurane (groups 1 and 2) or 1.2% isoflurane (groups 3 and 4) and nitrous oxide in oxygen (FIO₂, 0.33). TCD recordings of middle cerebral artery mean blood flow velocity (V(mean), cm/s) were taken before each respective treatment and for the 15-min investigation period. In groups 1 and 3 (each n = 20), the patients were exposed to surgical stimulation (skin incision). In groups 2 and 4 (each n = 10), norepinephrine infusion (0.1 μg · kg^-1 · min^-1) was used to increase mean arterial blood pressure (MAP) to levels similar to those seen with surgical stimulation (groups 1 or 3). Body temperature and PET(CO₂) remained constant over time and did not vary between treatment groups. In groups 1 and 3, MAP increased 22 and 16% after surgical stimulation. In groups 2 and 4, MAP increased 28 and 36% after norepinephrine infusion. V(mean) was increased 23 and 17% after surgical stimulation during 1 and 2 MAC isoflurane but did not change with norepinephrine infusion. These data show that cerebral blood flow velocity increases with surgical stimulation in 1 and 2 MAC isoflurane-anesthetized patients. This is not a function of changes in MAP. These data suggest that surgical stimulation increases cerebral blood flow, possibly because of arousal.