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 less than or equal to 2. Results: Cerebral blood now (CBF: Xe-133 inhalation technique), jugular bulb oxygen saturation (SjO(2)) 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. SjO(2) 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.