• L Meng, A W Gelb, B S Alexander, A E Cerussi, B J Tromberg, Z Yu, and W W Mantulin.
• Department of Anesthesiology and Perioperative Care, University of California Irvine Medical Center, Orange, CA 92868, USA. meng.lingzhong@gmail.com
• Br J Anaesth. 2012 May 1;108(5):815-22.

BackgroundMultiple studies have shown that cerebral tissue oxygen saturation (Sct(O(2))) is decreased after phenylephrine treatment. We hypothesized that the negative impact of phenylephrine administration on Sct(O(2)) is affected by arterial blood carbon dioxide partial pressure (Pa(CO(2))) because CO(2) is a powerful modulator of cerebrovascular tone.MethodsIn 14 anaesthetized healthy patients, i.v. phenylephrine bolus was administered to increase the mean arterial pressure ~20-30% during hypocapnia, normocapnia, and hypercapnia. Sct(O(2)) and cerebral blood volume (CBV) were measured using frequency domain near-infrared spectroscopy, a quantitative technology. Data collection occurred before and after each treatment.ResultsPhenylephrine caused a significant decrease in Sct(O(2)) during hypocapnia [ΔSct(O(2)) =-3.4 (1.5)%, P<0.001], normocapnia [ΔSct(O(2)) =-2.4 (1.5)%, P<0.001], and hypercapnia [ΔSct(O(2)) =-1.4 (1.5)%, P<0.01]. Decreases in Sct(O(2)) were significantly different between hypocapnia, normocapnia, and hypercapnia (P<0.001). Phenylephrine also caused a significant decrease in CBV during hypocapnia (P<0.01), but not during normocapnia or hypercapnia.ConclusionThe negative impact of phenylephrine treatment on Sct(O(2)) and CBV is intensified during hypocapnia while blunted during hypercapnia.

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