Early Recognition of Hypermagnesemia-Induced Prolonged Muscle Relaxation and Delayed Arousal Through Ionized Magnesium Measurement.

Hypermagnesemia is often iatrogenic and special attention is required in patients taking magnesium oxide, particularly those with impaired renal function or gastrointestinal obstruction. We report a case of a 60-year-old man who developed obstructive ileus due to sigmoid colon cancer. He had been prescribed magnesium oxide (2000 mg/day) and magnesium citrate (34 g) preoperatively. Postoperatively, he exhibited prolonged muscle relaxation and delayed awakening. Blood gas analysis revealed a significantly elevated ionized magnesium level of 3.53 mmol/L (reference range: 0.45-0.67 mmol/L). Continuous hemodiafiltration was promptly initiated, leading to patient awakening on postoperative day one and transfer to the general ward on postoperative day three. Retrospective analysis confirmed a total serum magnesium level of 14.1 mg/dL (reference range: 1.8-2.4 mg/dL) immediately after surgery. In this case, magnesium oxide accumulation due to obstructive ileus, combined with renal impairment caused by septic shock, likely contributed to the development of hypermagnesemia. The use of a blood gas analyzer capable of measuring ionized magnesium allowed for early recognition and early therapeutic intervention. This case highlights the risk of hypermagnesemia even with short-term magnesium oxide use in patients with gastrointestinal obstruction or renal dysfunction. Furthermore, it underscores the importance of magnesium monitoring in critically ill patients and the utility of ionized magnesium measurement in clinical practice.