Brain energy metabolism during controlled reduction of cerebral perfusion pressure in severe head injuries

Objective: To study cerebral biochemical markers with intracerebral microdialysis and bedside analysis in patients with severe head injuries treated with a controlled reduction of cerebral perfusion pressure (CPP). Design: Prospective observational study. Setting: Neurological intensive care unit in a university hospital. Patients: A consecutive series of 48 patients with severe head injuries and intracranial pressure (ICP) above 20 mmHg after conventional treatment. Interventions: Reduction of CPP was attained with i.v. infusion of beta (1)-antagonist (metoprolol) and an alpha2-agonist (clonidine). One microdialysis catheter was inserted via a burr hole frontally to that used for the intraventricular catheter ("better" position). In 27 patients one or more catheters were inserted into cerebral cortex surrounding an evacuated focal contusion or underlying an evacuated haematoma ("worse" position). Perfusion rate was 0.3 mul/min and samples were taken every 30 or 60 min. The levels of glucose, pyruvate, lactate, glycerol and glutamate were analysed and displayed bedside. Results: After initiation of treatment mean CPP decreased from 73 to 62 mmHg. During the first 96 h CPP was less than 60 mmHg and less than 50 mmHg during 30% and 8% of the time, respectively. The treatment was associated with a gradual normalisation of all biochemical markers in the "better" as well as the "worse" catheter position. Conclusion: The study shows that pharmacological decrease in CPP according to the "Lund concept" is associated with a normalisation of cerebral metabolism. The study also indicates that intracerebral microdialysis can be used for evaluation of new treatment strategies.