Blood-free magnesium concentration declines following graded experimental traumatic brain injury.

Traumatic brain injury has been shown to result in a decrease in brain-free magnesium concentration that is associated with the development of neurologic motor deficits. Although these changes have been well characterized in the brain, changes in free magnesium homeostasis have not been characterized in other fluid compartments. The current experiments use ion selective electrodes to measure alterations in blood-free magnesium concentration following graded experimental brain injury in rats and to compare these changes with subsequent neurologic outcome. After severe impact-acceleration-induced injury, blood-free magnesium levels significantly declined (p < 0.05) by 25% and remained depressed for at least 4 days after injury. After moderate injury, the decline in blood-free magnesium was less than that observed in the severe injury group with respect to both degree of decline and duration of decline. The post-traumatic blood-free magnesium concentration correlated to observed motor deficits as assessed by rotarod evaluation (p < 0.001). We conclude that blood-free magnesium levels may be a prognostic indicator of outcome following severe traumatic brain injury.