Hypovolemic hypotonic hyponatremia

Possible intestinal leak/perforation, diffuse peritonitis, sepsis, mild dehydration, and hypovolemic hypotonic hyponatremia... 

Patients with hypovolemic hypotonic hyponatremia should be treated with 0.9% saline, initially at infusion rates of200 to 400 mL/hour until symptoms... 

Patients with hypovolemic hypotonic hyponatremia, on the other hand, should be treated with normal saline because the concentration of osmotically effective urine cations is invariably less than that of isotonic saline. In contrast to patients with SIADH, sodium is avidly reabsorbed throughout the nephron when the effective circulating blood volume is decreased. Thus the urine osmolality is primarily comprised of urea, and the concentration of urine sodium is often less than 20 ruEq/L. 

Hypovolemic hypotonic hyponatremia— fluid and solute loss, with more sodium than water lost so that the remaining body fluid is hypotonic (dilute). May occur in hemorrhage or loss of vascular volume owing to gastrointestinal or renal loss (particularly owing to diuretic use). 

Hypotonic hyponatremia, the most common form of hyponatremia, can be further classified as hypovolemic, euvolemic, or hypervolemic hyponatremia. 

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