9/10/15 – Morning Report – Hyponatremia

  • Important to determine whether serum is hypo-osmolar, iso-osmolar, or hyperosmolar.
  • If hypo-osmolar, determine overall fluid status.
  • Using urine osmolality and urine sodium can assist with history and physical to determine etiology
  • Patients with significant vomiting can present with very low chloride levels (<60) due to high concentration of chloride within gastric lumen. Parietal cells secrete HCl into stomach lumen so excessive vomiting can significantly decrease serum chloride levels.
  • Metabolic alkalosis and hypokalemia can result from excessive vomiting. Hypokalemia could also be worsened with intracellular shift due to alkaline conditions.
  • Main trigger for renin aldosterone system is low volume status.
  • Main trigger for ADH secretion is elevated osmolality. Second trigger is low volume status.
  • Low volume status results in a higher urine osmolality and low urine sodium level, in the setting of proper renal function.
  • Low volume status with low solute intake (as in alcoholics) may display lower values of urine osmolality in addition to low urine sodium level.
  • May check urine chloride in a patient with hyponatremia, hypokalemia, and alkalosis:
    • If urine chloride low, suggestive of excessive vomiting.
    • If urine chloride high, suggestive of diuretic use.
    • If urine chloride normal, suggestive of possible Gitelman/Barttner syndrome

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