Hypertonic Mannitol-Induced Hyperkalemia during Craniotomy

We experienced two cases of mannitol-induced hyperkalemia during craniotomy for ruptured aneurysms. Hyperkalemia was first diagnosed by peaked T wave on the ECG. Serum potassium concentration in each patient was approximately 2 mEq/l higher than the baseline value, reaching 6.0 and 5.7 mEq/l, respectively, at 2 hours after completion of infusion of 45 and 30 g mannitol, respectively. Although the underlying mechanism was not elucidated, we recommend that patients with potassium concentration more than 4 mEq/l before infusion, should undergo repeated arterial blood gases analysis until at least 2 hrs after completion of mannitol infusion.