Effects of catecholamines on cerebral blood vessels in patients with traumatic brain injury.

Data on the cerebrovascular effects of catecholamines after head injury are difficult both to interpret and to compare. Diverse parameters with regard to brain trauma animal models, methods of determining the effects on the cerebral blood flow and metabolism and choice of end-points have been used. Many studies investigate the cerebrovascular effects of catecholamines over a range of cerebral perfusion pressures above the range recommended by current guidelines. The relationship between patient outcome and the use of a specific substance to improve cerebral perfusion has not been investigated. Dopamine, norepinephrine and phenylephrine all seem to increase cerebral blood flow in various animal models and in patients. The data suggest that norepinephrine may be the most predictable. It is associated with an improved restoration of global and regional oxygenation when compared to dopamine. Dopamine has been associated with an increase in brain oedema. There is further evidence that dopamine has many disadvantages in critically ill patients due to its ability to suppress circulating concentrations of most anterior pituitary-dependent hormones. Both aspects would further discourage its use. Data on phenylephrine are scarce. It has been associated with increased intracranial pressure and a failure to improve cerebral oxygenation despite markedly improved cerebral perfusion pressure. For all other catecholamines and related substances there are insufficient data on the cerebrovascular effects after head injury. This suggests that norepinephrine may be the catecholamine that is the most suitable substance to maintain or restore adequate cerebral perfusion. The data, however, are insufficient to formulate a guideline.