Detection of arrhythmogenic cellular magnesium depletion in hip surgery patients

The use of high-dose magnesium infusions in critically ill and surgicalpatients is increasing. This practice is associated with considerable riskof toxicity, as no reliable criteria are currently available to detectsignificant intracellular magnesium depletion. We have evaluated, beforeand after surgery, 33 elderly patients with hip fracture, by 24-h HolterECG monitoring, Doppler echocardiography and serum chemistry; lymphocytemagnesium was measured using atomic absorption spectrophotometry. Theseverity of ventricular arrhythmias increased, and serum and mononuclearmagnesium concentrations decreased significantly after surgery. Decreasesin either serum magnesium concentrations > 0.125 mmol litre-1 orcellular magnesium > 6 nmol mg- 1, but not serum or lymphocyte absolutemagnesium concentrations, were associated with postoperative development ofrepetitive arrhythmias. Variations in serum magnesium concentrationscorrelated with intracellular decreases, and yielded good accuracy inpredicting the postoperative worsening of arrhythmias. Thus perioperativedifferences in serum magnesium concentrations reflected intracellularvariations and allowed us to identify patients with clinically relevantcellular magnesium depletion.