An interesting study on nine healthy volunteers demonstrated noradrenaline infusions to increase MAP without increasing cardiac output (by increasing systemic vascular resistance). Measures of cerebral (frontal lobe) oxygenation, jugular venous saturation, and mean flow velocity in the middle cerebral artery all reduced with increasing doses of noradrenaline. The authors conclude that doses greater than 0.1 mcg/kg/min may reduce cerebral oxygenation. However increases in noradrenaline lowered paCO2 (through increases pulmonary ventilation) and it is unknown whether this was the major contributor to reduced oxygenation. It is also hard to ascertain the relevance to patients receiving noradrenaline, who unlike the healthy volunteers are not driven to supranormal blood pressures. In the meantime we will continue to attempt to optimise cerebral perfusion pressure using vasoactive drugs, but should be mindful that gross estimates of CPP may not tell us what we’re doing to cerebral oxygenation.
Br J Anaesth. 2009 Jun;102(6):800-5