Effect of phenylephrine on the haemodynamic state and cerebral oxygen saturation during anaesthesia in the upright position.

Background: The upright sitting or beachchair position is associated with hypotension, risk of cerebral hypoperfusion, and cerebral injury. We hypothesized that by increasing arterial pressure with phenylephrine administration, cerebral perfusion, and postoperative recovery would be improved.

Methods: Thirty-four patients undergoing elective shoulder surgery were randomized to receive either saline or phenylephrine infusion (PE) 5 min before being placed in the upright position. Simultaneous measurements of mean arterial pressure, cerebral oxygen saturation, middle cerebral artery velocity, and cardiac function using transthoracic echocardiography were made. Postoperative neurocognitive function was assessed.

Results: At the commencement of PE, mean (SD) cerebral oxygen saturation significantly decreased from 77 (10) to 67 (13)% (P=0.02), and further to 59 (11) % on upright positioning. The level of cerebral saturation upright was not significantly different to patients receiving saline (P=0.07), with values remaining at room-air levels. Middle cerebral artery blood velocity increased by 20% (P=0.04). Phenylephrine prevented hypotension in the upright position primarily by maintaining preload and increasing systemic vascular resistance (P=0.01), and was associated with a decrease in cardiac output. No postoperative neurocognitive dysfunction was identified.

Conclusions: Despite maintaining arterial pressure with phenylephrine, cerebral desaturation occurred with upright positioning. Cerebral oxygen saturation can provide a valuable endpoint when evaluating the effect of vasopressor therapy on cerebral perfusion.