Hyponatremia Vs Hypernatremia

Serum sodium is a concentration: it reflects the relationship between body sodium and body water, not simply how much sodium is in the body. Hyponatremia is a serum sodium concentration below 135 mEq/L; hypernatremia is above 145 mmol/L. Either disorder can become a neurologic emergency because water shifts across cell membranes and changes brain-cell volume. The number is only the beginning of the assessment. Ask how quickly it developed, whether the patient is hypovolemic, euvolemic, or hypervolemic, and whether neurologic symptoms are present. Acute disturbances develop in less than 48 hours; chronic disturbances have been present for 48 hours or longer. Duration matters because the brain adapts to a sustained sodium abnormality, making overly rapid correction dangerous. A postoperative patient who received excess free water may become confused and seize as sodium falls. An older adult with impaired thirst and limited access to fluids may become lethargic, intensely thirsty, and hypotensive as sodium rises. Both patients require more than a replacement value; they require a response matched to the direction of the abnormality, its duration, the volume assessment, and the...