マンニトール投与後の低ナトリウム血症の鑑別のため血漿浸透圧を測定し，治療方針を決定した1症例

The Measurement of Plasma Osmolality for the Differential Diagnosis of Hyponatremia due to Mannitol Administration and the Determination of the Treatment Strategy：A Case Report

要旨

　脳神経外科手術ではマンニトールが頻用されるが，投与後に電解質異常を来す場合がある。今回，開頭腫瘍摘出術中のマンニトール投与後に，血漿浸透圧の実測値と計算値に乖離を伴う高張性低ナトリウム血症を呈した症例を経験した。マンニトール投与後に血漿浸透圧を評価する場合は浸透圧ギャップに注意が必要である。

　Mannitol is frequently used in neurosurgical procedures, but its administration can sometimes cause electrolyte abnormalities. We treated a 60-year-old woman who exhibited hypertonic hyponatremia following an administration of mannitol during a craniotomy for tumor resection. A discrepancy was observed between the measured and calculated values of the patient’s plasma osmolality. This case demonstrates that when a patient’s plasma osmolality is evaluated after an administration of mannitol, close attention must be paid to the potential osmolality gap. In this case, we decided to monitor the patient without administering sodium replacement, and the hyponatremia eventually resolved.