PEDIATRICS Vol. 114 No. 6 December 2004, pp. 1744-1745 (doi:10.1542/10.1542/peds.2004-1791)
Hospital-Acquired Hyponatremia Is Associated With Excessive Administration of Intravenous Maintenance Fluid: In Reply
Desmond Bohn, MB, FRCPCEwout Hoorn, MD
Department of Critical Care Medicine
Hospital for Sick Children
Toronto, Ontario, Canada M5G 1X8
Mitchell L Halperin, MD, FRCPC
Division of Nephrology
St Michael’s Hospital
Toronto, Ontario, Canada M5V 1A6
The correspondence of Roberts and Hatherill et al1 in response to our study2 raises some important points that we feel require additional clarification. Their focus is on maintenance-fluid administration. Although there are comments in their letters and in the article by Moritz and Ayus3 about needs for sodium, this is a separate issue, and we shall not address it in our reply.
In both letters, the central issue is that all hospitalized children who do not have free access to water intake require maintenance-fluid administration. A second issue emphasized by Roberts is that there are sufficiently accurate data to provide guidelines for maintenance-fluid recommendations.
Issue of agreement: Humans produce heat during metabolism, and this heat must be lost to maintain a steady state. One of the means to lose heat is by evaporation of water; thus, there is an obligatory need for this form of water loss.
Issues for which there is disagreement:
- Loss of water from the lungs represents a deficit of water from the body. As summarized in our recently published article,4 we believe this is incorrect. Because the oxidation of carbohydrate and fat yield CO2 and H2O in a 1:1 stoichiometry, and their concentrations in alveolar air are also in a 1:1 stoichiometry (PCO2: 40 mm Hg; PH2O: 47 mm Hg), there is no deficit of water when production equals excretion.
- One cannot extrapolate from an estimate of caloric expenditure how much evaporation of water must occur to dissipate the heat produced in a patient. For example, heat production depends on activity, the metabolic demand to transform ingested nutrients into storage compounds, and how much uncoupling of oxidative phosphorylation is present. The latter is said to be
25% of resting energy expenditure in the rat,5 but this is just a crude guess for humans (for review, see ref 4).
In addition, consider the quantitative contribution of evaporative water loss to heat dissipation. In a normal adult, the volume of sweat at rest is said to be 500 mL/day. When this volume evaporates, one dissipates only 1050 kJ,6 an amount equal to only 10% of nonexercising caloric expenditure! Therefore, 90% of heat dissipation occurs by conduction, convection, and radiation. These latter processes are influenced by how much skin is exposed to air as well as the speed of air currents that favor evaporative cooling.6 Moreover, not all sweat will evaporate on the skin, because some will be adsorbed on the bedding.
Therefore, because one does not know the rate of heat production or the amount of heat that must be dissipated by water evaporation, one cannot deduce how much sweat loss there should be in an individual patient. Thus, one has only a crude guess of the volume of maintenance fluids needed by an individual patient, especially if that patient has an abnormal body temperature or the intake of drugs that can affect heat production.
- Even if we assume that evaporation of water was needed for thermoregulation, is it reasonable to assume that we must administer water for this physiologic effect? For example, if a patient has a surplus of water in cells, why not evaporate this "extra water" for this purpose? The best way to identify a surplus of water in cells is to have a low plasma sodium (Na) concentration (PNa).7 Although one could argue about a specific number, we suggest that if the PNa is appreciably less than 138 mM, do not administer exogenous maintenance fluids; let that patient rid themselves of their surplus water! You can tell when they need an exogenous source of water—when their PNa approaches 140 mM. In practical terms, we do not recommend that every child have a PNa measurement. Rather, if 10% of body water will be administered, one should measure the PNa to guide therapy.
We wish to emphasize 2 additional points.
- Too many patients die from our current, and inappropriate at times, administration of hypotonic intravenous fluids. Therefore, rather than just blaming this on excessive fluid administration according to guidelines, one must also suspect that the guidelines are overly "generous" for certain patients.
- There is no "1 size fits all" for an intravenous fluid-administration prescription. Physicians must decide on the best information for their patients, and we contend that the PNa provides the best indication of the benefits of and risks for hypotonic fluid administration.
As Sterns and Silver8 pointed out in their article "Salt and Water—Read the Package Insert," which accompanied our opinion piece,4 we should think of salt and water administration the same way we prescribe drugs. They went on to state that "prescribing hypotonic saline to a patient with a serum sodium concentration that is low and falling is the moral equivalent of giving warfarin to a patient with a high INR." We agree.
REFERENCES
- Hatherill M, Waggie Z, Salie S, Argent A. Hospital-acquired hyponatremia is associated with excessive administration of maintenance fluid [letter].
Pediatrics. 2004;114
:1368
[Free Full Text] - Hoorn EJ, Geary D, Robb M, Halperin ML, Bohn D. Acute hyponatremia related to intravenous fluid administration in hospitalized children: an observational study.
Pediatrics. 2004;113
:1279
–1284
[Abstract/Free Full Text] - Moritz ML, Ayus JC. Prevention of hospital-acquired hyponatremia: a case for using isotonic saline.
Pediatrics. 2003;111
:227
–230
[Abstract/Free Full Text] - Shafiee MA, Bohn D, Hoorn EJ, Halperin ML. How to select optimal maintenance intravenous fluid therapy.
QJM. 2003;96
:601
–610
[Abstract/Free Full Text] - Brand MD. Uncoupling to survive? The role of mitochondrial inefficiency in ageing. Exp Gerontol. 2000;35 :811 –820[CrossRef][Web of Science][Medline]
- Schmidt-Nielson K. Animal Physiology: Adaptation and Environment. 5th ed. Cambridge, United Kingdom: Cambridge University Press; 1997
- Halperin ML, Goldstein M. Fluid, Electrolyte and Acid Base Physiology: A Problem-Based Approach. 1998, Philadelphia, PA: W. B. Saunders
- Sterns RH, Silver SM. Salt and water: read the package insert.
QJM. 2003;96
:549
–552
[Free Full Text]
PEDIATRICS (ISSN 1098-4275). ©2004 by the American Academy of Pediatrics
CiteULike 
Connotea 
Del.icio.us 
Digg 
Facebook 
Reddit 
Technorati 
Twitter What's this?
Related articles in Pediatrics:
- Hospital-Acquired Hyponatremia Is Associated With Excessive Administration of Intravenous Maintenance Fluid
- Kenneth B. Roberts
Pediatrics 2004 114: 1743-1744.[Extract] [Full Text]
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
