Hypomagnesemia and hypophosphatemia at admission in patients with severe head injury

Objective: Low serum levels of electrolytes such as magnesium (Mg), potassium (K), calcium (Ca), and phosphate (P) can lead to a number of clinical problems in intensive care unit (ICU) patients, including hypertension, coronary vasoconstriction, disturbances in heart rhythm, and muscle weakness. Loss of these electrolytes can be caused, among other things, by increased urinary excretion. Cerebral injury can lead to polyuresis through a variety of mechanisms. We hypothesized that patients with cranial trauma might be at risk for electrolyte loss through increased diuresis. The objective of this study was to assess levels of Mg, P, and K at admission in patients with severe head injury. Design: We measured plasma levels of Mg, P, K, Ca, and sodium at admission in 18 consecutive patients with severe head injury admitted to our ICU (group 1). As controls, we used 19 trauma patients with two or more bone fractures but no significant cranial trauma (group 2). Setting: University teaching hospital. Patients: Eighteen patients with severe head injury admitted to our surgical ICU (group 1) and 19 controls (trauma patients with no significant cranial trauma; group 2). Main Results: Electrolyte levels at admission (group 1 vs. group 2; mean ± SD, units: mmol/L) were as follows. Mg, 0.57 ± 0.17 (range, 0.24-0.85) vs. 0.88 ± 0.21 (range, 0.66-1.42 mmol/L; p < .01). P, 0.56 ± 0.15 (range, 0.20-0.92) vs. 1.11 ± 0.15 (range, 0.88-1.44 mmol/L; p < .01). K, 3.54 ± 0.59 (range, 2.4-4.8) vs. 4.07 ± 0.45 (range, 3.6-4.8 mmol/L; p < .02). Ca, 2.02 ± 0.24 (range, 1.45-2.51) vs. 2.14 ± 0.20 (range, 1.88-2.46; p = NS). In group 1, 12/18 patients had Mg levels