Effects of magnesium sulphate on cerebral haemodynamics in healthy volunteers: a transcranial Doppler study

Abstract

Magnesium is increasingly being considered as a neuroprotective agent. We aimed to study its effects on middle cerebral artery blood flow velocity (V(mca)), cerebral autoregulation and cerebral vascular reactivity to carbon dioxide (CRCO(2)) in healthy volunteers. Fifteen healthy volunteers were recruited. Using transcranial Doppler ultrasonography, V(mca) was recorded continuously. The strength of autoregulation was assessed by the transient hyperaemic response test, and the CRCO(2) was measured by assessing changes in V(mca) to the induced changes in end-tidal carbon dioxide. I.V. infusion of magnesium sulphate was then started (loading dose of 16 mmol followed by an infusion at the rate of 2.7 mmol h(-1)) for 45 min. The cerebral haemodynamic variables were measured again near the end of the infusion of magnesium sulphate. Total serum magnesium levels were doubled by the infusion regimen. However, there were no significant changes in V(mca), strength of autoregulation, or CRCO(2). Five of the volunteers reported marked nausea and two developed significant hypotension during the loading dose. Infusion of magnesium sulphate, in a dose that doubles its concentration in plasma, does not affect V(mca), strength of autoregulation or CRCO(2) in healthy volunteers. However, it can be associated with nausea and hypotension.