Preservation of cerebral oxidative metabolism in fulminant hepatic failure: an autoregulation study

Under normal conditions cerebral blood flow (CBF) is regulated to secure oxidative brain metabolism, but in patients with fulminant hepatic failure (FHF), insufficient CBF has been suggested to precede cerebral edema and intracranial hypertension. In order to determine if insufficient CBF and hypoxia are present in patients with FHF we increased the mean arterial pressure and measured cerebral metabolism. In six patients with FHF CBF determined by 133Xenon injection technique, transcranial Doppler mean flow velocity in the middle cerebral artery (Vmean) and cerebral metabolism were determined, before and after an increase in mean arterial pressure by norepinephrine infusion. Mean arterial pressure was measured in a radial artery, and blood samples from the radial artery and internal jugular vein allowed calculation of the cerebral arteriovenous oxygen (AVDO2), -glucose (AVDgl), and -lactate (AVDlac) differences. Cerebral metabolic rates (CMRO2,-gl,-lac) were calculated as AVDO2,-gl,-lac times CBF. Mean arterial pressure was raised from 70 (54-105) to 111 (93-128) mm Hg during intravenous infusion of norepinephrine. CBF increased from 34 (12-55) to 47 (27-81) mL . 100g-1. min-1 (p < 0.05) and Vmean from 53 (42-60) to 67 (61-79) cm.s-1 (p < 0.05), whereas CMRO2 (1.4 (0.9-2.4) mL . 100g-1 . min-1), CMRgl (11 (4.8-20) mumol 100g-1 . min-1), and CMRlac (3.2 (0-8.9) mumol . 100g-1 . min-1) remained unchanged. Our finding indicates that cerebral oxidative metabolism is preserved in patients with FHF. Cerebral autoregulation is absent, however, and neuroprotective critical care is suggested to be guided by internal jugular vein oxygen saturation to secure appropriate cerebral oxygenation.