Is cerebral oxygenation negatively affected by infusion of norepinephrine in healthy subjects?

Background: Vasopressor agents are commonly used to increase mean arterial pressure (MAP) in order to secure a pressure gradient to perfuse vital organs. The influence of norepinephrine on cerebral oxygenation is not clear. The aim of this study was to evaluate the impact of the infusion of norepinephrine on cerebral oxygenation in healthy subjects.

Methods: Three doses of norepinephrine (0.05, 0.1, and 0.15 microg kg(-1) min(-1) for 20 min each) were infused in nine healthy subjects [six males; 26 (6) yr, mean (SD)]. MAP, cerebral oxygenation characterized by frontal lobe oxygenation (Sc(O2)) and internal jugular venous oxygen saturation (Sjv(O2)), middle cerebral artery mean flow velocity (MCA Vmean), cardiac output (CO), and arterial partial pressure for carbon dioxide (Pa(CO2)) were evaluated.

Results: MAP increased from 88 (79-101) [median (range)] to 115 (98-128) mm Hg with increasing doses of norepinephrine (P < 0.05), reflecting an increase in total peripheral resistance [20.3 (12.2-25.8) to 25.2 (16.4-28.5) mm Hg min litre(-1); P < 0.05] since CO remained at baseline values. Sc(O2) and Sjv(O2) decreased with increasing doses of norepinephrine, reaching statistical significance with norepinephrine infused at 0.1 microg kg(-1) min(-1) [Sc(O2): 78 (75-94) to 69 (61-83)%; P < 0.05; Sjv(O2): 67 (8) to 64 (7)%; P < 0.01]. MCA Vmean was reduced with each dose of norepinephrine [56.9 (11.2) to 55.0 (11.7) cm s(-1); P < 0.05] and Pa(CO2) lowered from 5.4 (0.4) to 5.1 (0.4) kPa (P < 0.001).

Conclusions: This study suggests that infusion of norepinephrine at 0.1 microg kg(-1) min(-1) or higher may negatively affect cerebral oxygenation.