I have been interested in the impact of vasopressors on brain blood flow and oxygenation since a couple of years now. You can read a post related to previous work here, and pieces related this issue here and here.
Accumulating evidence, published by independent research teams, suggests that the utilization of some vasopressor agents can be associated with a reduction in brain oxygenation monitored by near-infrared spectroscopy. However, the picture isn’t that perfect because other research teams have published the opposite. In upcoming posts, I will discuss results related to that very exciting research area.
I will begin with a small correspondence published last year in the British Journal of Anaesthesia. In this study, phenylephrine (50–100 mg; n=4) and ephedrine (5–10 mg; n=7) were administered in patients undergoing carotid endarterectomy under general anesthesia, in order to correct hypotension (corresponding to a 20% reduction in mean arterial pressure (MAP) vs. preoperative MAP before cross-clamping). MAP, middle cerebral artery flow velocity (MCAVmean; transcranial Doppler) and cerebral oxygenation (near-infrared spectroscopy) were monitored.
The figure below shows the main results of this study.
MAP augmented with both vasopressor agents. Following administration of ephedrine, MCAVmean stayed constant and cerebral oxygenation (rSO2) increased. However, MCAVmean increased while cerebral oxygenation decreased following the administration of phenylephrine. Of interest, heart rate raised with ephedrine and dropped with phenylephrine.
The authors suggest that this reduction in cerebral oxygenation with phenylephrine may be explained by 1) a change (decrease) in cardiac output following administration of this vasopressor or 2) a direct alpha-receptor-mediated cerebral vasoconstriction.
Although the data are very limited, the observations were consistent, since no patients treated with phenylephrine showed an increase in cerebral oxygenation, and no patient in the ephedrine group showed a decrease.
Pennekamp CW, Immink RV, Moll FL, Buhre WF, de Borst GJ. Differential effect of phenylephrine and ephedrine on cerebral haemodynamics before carotid cross-clamping during carotid endarterectomy. Br J Anaesth 2012 109(5):831-3. doi: 10.1093/bja/aes370.