A 61-year-old man had hyponatremia (serum Na 112 mmol/L), which was associated with disturbance of consciousness. Therefore, administration of hypertonic saline was commenced. Eventually he was diagnosed with the syndrome of inappropriate secretion of antidiuretic hormone (SIADH). Hypertonic saline was continued for 45 days, and plasma Na concentration rose to 138 mmol/L. At that time we were consulted regarding further administration of hypertonic saline. At the time of the consultation marked edema had developed affecting the whole body. The cardiothoracic ratio was increased and pleural effusion was evident on the chest X-ray. Administration of hypertonic saline was discontinued to prevent further worsening of the edema. Furthermore, water restriction (500 mL/day) was started. Body weight decreased by 4.3 kg in 7 days and the edema was diminished. However, plasma Na concentration decreased to 117 mmol/L. At that stage, we needed to balance the treatment of hyponatremia to the increased extracellular fluid volume (ECF). To normalize the ECF, we carried out ultrafiltration (UF) three times. Resolution of edema by using an extracorporeal UF method allowed the control of plasma Na concentration. In this case increased ECF volume hindered the adjustment of plasma Na concentration. The infusion of hypertonic saline is now used commonly by physicians. It is necessary to consider the potential risks of such treatment.
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