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Isotonic Saline Expands Extracellular Fluid and Is Inappropriate for Maintenance Therapy

2005; American Academy of Pediatrics; Volume: 115; Issue: 1 Linguagem: Inglês

10.1542/peds.2004-1769

1098-4275

Malcolm A. Holliday,

Renal function and acid-base balance

To the Editor.—The article by Hoorn et al1 surveys the frequency of hyponatremia in children seen in the emergency department of a large children's hospital. The survey included children who were hyponatremic on presentation (6% of 1586) and those who became hyponatremic when given intravenous (IV) fluid therapy (9% of 432). Both groups had nonosmotic (mostly hypovolemic) stimulated antidiuretic hormone (ADH) release and received electrolyte free water in excess of a renal excretory capacity, limited by ADH.My colleagues and I2 recently reviewed evidence that rapid and generous expansion of extracellular fluid (ECF) suppresses ADH in acutely ill children with subtle hypovolemia, which is similar to that seen in severe dehydration, burn shock, and septic shock, although much less intense. Once ECF is expanded, IV maintenance therapy can be given safely in the recommended amounts using hypotonic saline. We concluded that the key to preventing hyponatremia is suppressing ADH before undertaking maintenance therapy.This approach differs from the authors and that of Moritz and Ayus,3 who recommend using isotonic saline as generic maintenance fluid. Although initially accomplishing the same goal, it needlessly distorts the meaning of the term "maintenance" therapy and confuses follow-up planning. The term "maintenance" was derived by Gamble, Darrow, Butler, and others in the 1940s (see ref 4) to describe replacement needs for insensible and urinary losses after rehydration (ECF expansion). Segar and I4 then found an easy way to derive metabolic rate from body weight in 420-kcal increments and to define average maintenance therapy in easily remembered terms.On the other hand, using isotonic saline as generic maintenance therapy imposes an IV sodium-chloride load that substantially increases when IV maintenance therapy is extended beyond the first day. This can cause hypernatremia, which, similar to hyponatremia, results in brain injury or death (as pediatricians active 40 years ago vividly remember).To restore ECF before maintenance therapy is begun, many emergency departments initially give isotonic saline, ∼5 mL/kg per hour for 6 to 12 hours. After this, maintenance needs often can be met by oral fluids, but they will be safely met by IV maintenance therapy when given in recommended amounts. We proposed the more robust response of giving isotonic saline at a rate of 10 mL/kg per hour for 2 to 4 hours. This rapidly and safely expands ECF, suppresses ADH if elevated, and initiates normal urine flow.