Effects of hypertonic saline on intracranial pressure variables in subarachnoid haemorrhage patients

Abstract

Elevated intracranial pressure (ICP) and reduced cerebral perfusion pressure (CPP) can be life threatening for patients suffering from acute subarachnoid haemorrhage (SAH). Osmotherapy can be used in these situations. Three clinical studies looking at the effects of intravenous hypertonic saline (HS) on intracranial pressure variables in SAH patients form the basis for this thesis in neuro intensive care medicine.<br><br>

The main aim of osmotherapy is to reduce the water content of the brain, creating a more favourable compliance situation and allowing adequate brain perfusion. Mannitol has been the drug of choice, but evidence is emerging that HS might be a better alternative. However, the use of HS in SAH patients has not been studied systematically. The first main aim of this thesis was to describe the effects of HS on mean ICP and CPP, both the magnitude and the temporal pattern. The second main aim was to compare the effect of HS on mean ICP with the effect on mean ICP wave amplitude (intracranial pulse pressure). This variable can like mean ICP be monitored continuously at the bedside and reflects better the intracranial compliance situation than does the mean ICP.<br><br>

Intravenous bolus infusion of 2 mL/kg of 7.2% saline in 6% hydroxyethyl starch in SAH patients reduced elevated mean ICP by more than 50% at time of maximum effect and increased CPP correspondingly. This occurred 20 – 30 minutes after the end of the infusion, and average mean ICP was still below baseline after 3 hours. Both observational and placebo controlled data supports these findings. Infusion of HS also reduces mean ICP wave amplitude. There was however poor agreement between mean ICP and mean ICP wave amplitude. Even though a target level for mean ICP was reached in most cases, this was not the case for the pulse pressure. This suggests that the intracranial compliance may be less favourable than expected in many SAH patients with normal mean ICP.