Magnesium Concentration in Cerebrospinal and Brain Interstitial Fluid Correlates with Serum Level in Induced Hypermagnesemia

Being a modulator of the N-methyl-D-aspartate (NMDA) receptor function magnesium has been studied for its neuroprotective and vasodilatative properties in acute and delayed brain ischemia due to vasospasm in aneurysmal subarachnoid haemorrhage (aSAH) and stroke. A number of clinical phase II and III studies have correlated serum magnesium concentrations after intravenous continuous application to clinical outcome and have failed to show a positive therapeutic effect. However, no study supported its conclusion by providing evidence for a local increase in magnesium, i.e. in the cerebrospinal fluid (CSF) and the brain parenchyma. The objective of our observational study was to compare magnesium levels in serum, CSF, and brain microdialysis samples (MDS) in patients with aSAH. Seventeen patients with aSAH at World Federation of Neurosurgeons (WFNS) grade IV and V were included. According to our internal standard treatment protocols, all patients received a ventricular catheter, a frontal intracerebral microdialysis probe, and a continuous intravenous application of 80 mmol MgSO₄ per 24 hours. Magnesium concentrations of serum, CSF, and MDS were recorded. We found a positive and significant correlation of increased serum levels of magnesium to CSF and MDS magnesium concentrations. These pharmacokinetic findings may serve as a basis for further discussion of the concept of induced hypermagnesemia in patients with aSAH, especially in the context of recent level A evidence of the lack of clinical benefit.