EFFECTS OF HYPOTENSIVE TREATMENT WITH ALPHA(2)-AGONIST AND BETA(1)-ANTAGONIST ON CEREBRAL HEMODYNAMICS IN SEVERELY HEAD-INJURED PATIENTS

Therapy of post-traumatic brain oedema often includes preservation of high arterial blood pressure to avoid secondary ischaemic injuries to the brain. This practice can be questioned since high arterial blood p ressure may aggravate brain oedema through raised hydrostatic capillar y pressure, causing fluid filtration across the damaged blood-brain ba rrier. This latter view is in agreement with our clinical experience a nd therefore hypotensive therapy with an alpha(2)-adrenergic agonist ( clonidine) and a beta(1)-adrenergic antagonist (metoprolol) has become part of our treatment protocol for severely head injured patients to decrease the post-traumatic brain oedema. The present study is an atte mpt to analyse whether there are any direct local cerebrovascular effe cts of the hypotensive agents used, which also might influence intracr anial pressure. Severely head injured patients were investigated. Hear t rate, mean arterial blood pressure, intracranial pressure, cerebral blood flow and arteriovenous difference in oxygen content were measure d before and after a bolus dose of clonidine (six patients) and metopr olol (nine patients). Clonidine decreased mean arterial blood pressure and cerebrovascular resistance without affecting other parameters mea sured. Metoprolol decreased heart rate and mean arterial pressure, but had no effect on the cerebrovascular parameters. The results show tha t clonidine and metoprolol have no, or only minor, direct influence on local cerebral haemodynamics in severely brain injured patients. This implies that if there is an intracranial pressure reducing effect of these drugs, as suggested, this must be due to other mechanisms, namel y a reduction in capillary hydrostatic pressure secondary to decreased arterial blood pressure and heart rate.