We evaluated the effects of magnesium sulfate on brain tissue oxygen (PtO2) 
tension, carbon dioxide (PtCO2) tension and pH (pHt) in patients undergoing 
temporary artery occlusion for clipping of cerebral aneurysm. We studied 18 
patients with aneurysmal subarachnoid hemorrhage. All patients received standard 
anesthetics using target controlled infusion of propofol (3 microg/ml) and 
remifentanil (10 ng/ml). After craniotomy, a calibrated multiparameter sensor 
(Neurotrend, Diametrics Medical, Minneapolis, MN) was inserted to measure PtO2, 
PtCO2 and pHt in tissue at risk of ischemia during temporary artery occlusion. 
Patients were then randomly allocated to receive either intravenous saline or 
magnesium 20 mmol over 10 min followed by an infusion 4 mmol/h. Plasma magnesium 
concentration, brain tissue gases and pHt were determined at baseline, 30 min 
after study drug infusion and 4 min after temporary clipping. Data were analyzed 
by factorial ANOVA with repeated measures. Intergroup difference was compared 
with unpaired t test. P value < 0.05 was considered significant. Patient 
characteristics, baseline brain tissue gases and pHt did not differ between 
groups. Magnesium infusion increased PtO2 by 34%. Following temporary artery 
occlusion, PtO2 and pHt decreased and PtCO2 increased in both groups. However, 
tissue hypoxia was less severe and the rate of PtO2 decline was slower in the 
magnesium group. Our data suggested that magnesium enhances tissue oxygenation 
and attenuates hypoxia during temporary artery occlusion.