Pathophysiology-hypernatremia

(Crit Care 2013;17:206; NEJM 2015;372:55)

• Deficit of water relative to sodium; by definition, all hypernatremic Pts are hypertonic
• Usually loss of hypotonic fluid (ie, “dehydration”);
• occasionally infusion of hypertonic fluid,
• post-ATN diuresis w/ loss of low or electrolyte-free water (Am J Neph 2012;36:97)
• And impaired access to free water (eg, intubation, Δ MS, elderly):
  • hypernatremia is a powerful thirst stimulus,
  • ∴ usually only develops in Pts w/o access to H2O or ill