It is likely worse to treat younginfants and toddlers with hypotonic intravenous (IV) fluid (D5 1/2 or D5 1/3), because hypo-osmotic fluids canlead to iatrogenic hyponatremia

It is likely worse to treat younginfants and toddlers with hypotonic intravenous (IV) fluid (D5 1/2 or D5 1/3), because hypo-osmotic fluids canlead to iatrogenic hyponatremia: Excerpt from Avoiding Common Pediatric Errors

Author: Madan Dharmar, MD

What to Do - Make a Decision

Acute gastroenteritis is one of the common illnesses affecting infants and children throughout the world. Correction of dehydration is the mainstay of treatment, which is given as oral rehydration therapy (preferably) or intravenous fluids, depending on the severity of dehydration and various other factors. It is imperative to correctly choose the type of fluid to avoid electrolyte disturbances that might lead to dangerous complications.

Among children in the United States, acute gastroenteritis remains a major cause of morbidity and hospitalization, accounting for >1.5 million outpatient visits, 200,000 hospitalizations, and approximately 300 deaths per year.

The volume of fluid lost through stools can vary from 5 mL/kg body weight per day,which is approximatelynormal, to >=200 mL/kg body weight per day, which is severe diarrhea. Dehydration and electrolyte losses associated with untreated diarrhea are the main reason for morbidity in acute gastroenteritis. History, physical examination, and dehydration assessment are the main features in the assessment of diarrhea. Treatment usually includes two phases: rehydration and maintenance. The rehydration phase involves quick replacement of fluids usually within 3 to 4 hours. The maintenance phase is the phase inwhich maintenance caloriesandfluids are administered. IV fluids are the mainstay of management in cases of severe dehydration.

IV fluid administration to maintain water and electrolyte balance in an individual was first described by Holliday and Segar in 1957. They had based the free water requirement on evidence that it equated the energy expenditure in healthy children. However, sodium and potassium requirements (3.0 and 2.0 mEq/100 kcal/24 hour, respectively) were rationalized based on intake of electrolytes by infants receiving breast and cow milk. Use of hypotonic IV fluids was based on the above recommendations. Although these recommendationsmay beappropriatefor thehealthychild,theydo not necessarily apply in acute illness, where energy expenditure and electrolyte requirements deviate significantly from that of a normal healthy individual. The calculation based on this recommendation could overestimate the hypotonic solution needs in patients.

Hyponatremiaoccurswhenthewatertosodiumratioisincreased,which means that the plasma sodium concentration is <136 mM. This can be either due to decrease in sodium or an increase in the water. This could occur when there is a positive balance of electrolyte free water in the body due to increased input of water than excretion of water. A decrease in the water output usually occurs secondary to antidiuretic hormone (ADH) secretion. In normal individuals, ADH is controlled by osmotic stimuli and hence water diuresis occurs only when the plasma sodium level falls below 136 mM (due to ADH suppression). However, hospitalized pediatric patients have multiple causes for nonosmotic stimuli for ADH secretion, and hence when the plasma sodium level falls below 136 mM, water diuresis does not take place due to the presence of ADH (nonosmotic stimuli) and this increases the available electrolyte free water in the body. Administration of hypotonic solution would further contribute to the electrolyte free water, leading to hyponatremia in these patients. It has been shown that patients admitted with gastroenteritis have obligate urinary sodium losses irrespective of initial serum sodium. The urinary tonicity at presentation of these patients is approximately equal to normal saline. Therefore, infusion of a hypotonic solution, which is lower in tonicity than that of urine passed, is predictive of a decrease in subsequent serum sodium.

Hyponatremia can cause water to move into the intercellular compartment, thereby causing the cells to swell. The expansion of intracellular fluid volume is of major importance in the central nervous system, as the brain is confined in a rigid bony cage and has only limited ability to expand. Thus, brain cell swelling is very likely to increase intracranial pressure and predispose to brain herniation. Children are at greater risk of this sequela because their brains have a larger intracellular fluid volume per total skull volume. The incidence of permanent brain damage is higher in children with symptomatic hyponatremia when compared to adults. Symptoms of cerebral edema include nausea, vomiting, agitation, headache, seizures, and coma. Choong et al. state that "based on published case reports of deaths and neurological injury from acute hyponatremia that the administration of hypotonic solutions to children with a PNa, 138 mmol/L is potentially hazardous, given that ADH is likely to be acting."

The administration of isotonic maintenance solution in certain cases has resulted in a more rapid return of ADH to normal concentrations, when compared to hypotonic fluids. Isotonic crystalloid solutions, such as lactated Ringer and normal saline, expand the fluid space and improve circulating volume without exacerbating hyponatremia, thereby decreasing the risk of cerebral edema. Isotonic fluids could cause hyponatremia during the perioperative period in a person who had been given Ringer lactate solution to prevent a fall in blood pressure by the process of desalination. However, administration of isotonic fluids in individuals who produced hypotonic urine could cause positive sodium, leading to hypernatremia.

In conclusion, the current recommendation for IV fluid management is not based on clinical experiment on hospitalized patients but rather was derived based on the normal homeostatic mechanismsinhealthy individuals. Thereisevidencethat,atleastinsomepediatricpatients,hypotonicsolutions exacerbate the risks of hyponatremia, whereas isotonic solutions may be protective. Taking these into account a judicious choice of fluid type should be made in the management of dehydration based on individual needs.

Suggested Readings

Choong K, Kho ME, Menon K, et al. Hypotonic versus isotonic saline in hospitalised children: a systematic review. Arch Dis Child. 2006;91(10):828–835.
HollidayMA,SegarWE. Themaintenanceneedforwaterinparenteral fluidtherapy. Pediatrics. 1957;19(5):823–832.
King CK, Glass R, Bresee JS, et al. Managing acute gastroenteritis among children oral rehydration,maintenance, and nutritionaltherapy. MMWRRecomm Rep. 2003;52(RR-16):1–16.
Moritz ML, Ayus JC. Prevention of hospital-acquired hyponatremia: a case for using isotonic saline. Pediatrics. 2003;111(2):227–230.
Shafiee MA, Bohn D, Hoorn EJ, et al. How to select optimal maintenance intravenous fluid therapy. QJM. 2003;96(8):601–610.
World Health Organization. The Treatment of Diarrhoea: A Manual for Physicians and Other Senior Health Workers. Geneva, Switzerland: World Health Organization; 2005.

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Book Source Details

• Book Title: Avoiding Common Pediatric Errors
• Author(s): Anthony D Slonim MD, DrPH; Lisa Marcucci MD
• Year of Publication: 2008
• Copyright Details: Avoiding Common Pediatric Errors, Copyright © 2008 Lippincott Williams & Wilkins.

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More About This Book: Title: Avoiding Common Pediatric Errors Authors: Anthony D Slonim MD, DrPH; Lisa Marcucci MD Publisher: Lippincott Williams & Wilkins Copyright: 2008 ISBN: 0-7817-7489-6

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