Cerebral blood flow and metabolism in severe brain injury: the role of pressure autoregulation during cerebral perfusion pressure management

Objective: To ascertain if norepinephrine can be used as part of the cerebral perfusion pressure (CPP) management to increase arterial blood pressure (MAP) without causing cerebral hyperemia after severe head injury (HI).¶Design: Prospective, interventional study.¶Setting: Intensive care unit in a university hospital.¶Patients: Twelve severely HI patients; median Glasgow Coma Scale was 6 (range 3–8).¶Interventions: CPP management ( = 70 mmHg). Pressure autoregulation (assessed by norepinephrine infusion) was defined intact if %CPP/%CVR ≤ 2.¶Results: Cerebral blood flow (CBF: Xe¹³³ inhalation technique), jugular bulb oxygen saturation (SjO₂) and transcranial Doppler (TCD) were recorded during the test. Norepinephrine increased CPP by 33 % ( ± 4). Autoregulation was found to be intact in ten patients and defective in two. In the ten patients with preserved autoregulation, CBF decreased from 31 ± 3 to 28 ± 3 ml/100 g/min; in the two patients with impaired autoregulation CBF increased respectively from 16 to 35 and from 21 to 70 ml/100 g/min. SjO₂ did not change significantly from baseline. TCD remained within the normal range.¶Conclusions: During CPP management norepinephrine can be used to increase MAP without potentiating hyperemia if pressure autoregulation is preserved. The assessment of pressure autoregulation should be considered as a guide for arterial pressure-oriented therapy after HI.