Impact of phenylephrine administration on cerebral tissue oxygen saturation and blood volume is modulated by carbon dioxide in anaesthetized patients †

BACKGROUND: Multiple studies have shown that cerebral tissue oxygen saturation ([Image: see text]) is decreased after phenylephrine treatment. We hypothesized that the negative impact of phenylephrine administration on [Image: see text] is affected by arterial blood carbon dioxide partial pressure ([Image: see text]) because CO(2) is a powerful modulator of cerebrovascular tone. METHODS: In 14 anaesthetized healthy patients, i.v. phenylephrine bolus was administered to increase the mean arterial pressure ∼20–30% during hypocapnia, normocapnia, and hypercapnia. [Image: see text] and cerebral blood volume (CBV) were measured using frequency domain near-infrared spectroscopy, a quantitative technology. Data collection occurred before and after each treatment. RESULTS: Phenylephrine caused a significant decrease in [Image: see text] during hypocapnia [[Image: see text]=−3.4 (1.5)%, P<0.001], normocapnia [[Image: see text]=−2.4 (1.5)%, P<0.001], and hypercapnia [[Image: see text]=−1.4 (1.5)%, P<0.01]. Decreases in [Image: see text] 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. CONCLUSION: The negative impact of phenylephrine treatment on [Image: see text] and CBV is intensified during hypocapnia while blunted during hypercapnia

Effect of phenylephrine and ephedrine bolus treatment on cerebral oxygenation in anaesthetized patients

BACKGROUND: How phenylephrine and ephedrine treatments affect global and regional haemodynamics is of major clinical relevance. Cerebral tissue oxygen saturation ([Image: see text])-guided management may improve postoperative outcome. The physiological variables responsible for [Image: see text] changes induced by phenylephrine and ephedrine bolus treatment in anaesthetized patients need to be defined. METHODS: A randomized two-treatment cross-over trial was conducted: one bolus dose of phenylephrine (100–200 µg) and one bolus dose of ephedrine (5–20 mg) were given to 29 ASA I–III patients anaesthetized with propofol and remifentanil. [Image: see text], mean arterial pressure (MAP), cardiac output (CO), and other physiological variables were recorded before and after treatments. The associations of changes were analysed using linear-mixed models. RESULTS: The CO decreased significantly after phenylephrine treatment [▵CO=−2.1 (1.4) litre min(−1), P<0.001], but was preserved after ephedrine treatment [▵CO=0.5 (1.4) litre min(−1), P>0.05]. The [Image: see text] was significantly decreased after phenylephrine treatment [▵[Image: see text]=−3.2 (3.0)%, P<0.01] but preserved after ephedrine treatment [▵[Image: see text]=0.04 (1.9)%, P>0.05]. CO was identified to have the most significant association with [Image: see text] (P<0.001). After taking CO into consideration, the other physiological variables, including MAP, were not significantly associated with [Image: see text] (P>0.05). CONCLUSIONS: Associated with changes in CO, [Image: see text] decreased after phenylephrine treatment, but remained unchanged after ephedrine treatment. The significant correlation between CO and [Image: see text] implies a cause–effect relationship between global and regional haemodynamics