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Carlos Ayus, MD
Department of Medicine
University of Texas Health Science Center
San Antonio, TX 78229-3900
We welcome the comments of Hatherill et al, because they agree with our main contention,1 ie, that the current practice of administering hypotonic maintenance parenteral fluid therapy to children can lead to dangerous hyponatremia and is in need of change. Where we differ, however, is in how we propose to change it. Hatherill et al suggest reducing the volume of maintenance fluid rather than using isotonic saline.2 Although it is true that fluid restriction will prevent hyponatremia, we are concerned that this practice could cause harm by perpetuating a state of subclinical volume depletion. Volume depletion is common in children who are unable to take enteral fluids, and it can be difficult to assess on clinical grounds.3 Using 0.9% NaCl is the most physiologic approach, because it is an excellent volume expander and does not provide unnecessary free water, which can lead to hyponatremia.
Hatherill et al ask for evidence showing that isotonic maintenance fluids are effective in preventing hospital-acquired hyponatremia. Prospective studies in both children and adults undergoing major surgery have shown that patients who receive 0.9% NaCl do not develop hyponatremia, whereas patients who receive a more hypotonic fluid, including lactated Ringer's solution (sodium: 131 mEq/L), have a fall in serum sodium.4–7 This is significant, because postoperative patients are at the highest risk for developing hyponatremic encephalopathy.8
Hatherill et al surmise, based on the article by Hoorn et al,9 that the main factor that results in hyponatremia is excess fluid administration. In fact, it is a misrepresentation by Hoorn et al that 73% of patients with hyponatremia received "more than recommended maintenance"9 fluids, because the fluid volume reported included both deficit and maintenance therapy. Forty percent of these patients received 45 mL/kg 0.9% NaCl boluses. Additionally, there were more surgical patients in the hyponatremia group than in the control group. It is well known that intraoperative fluid requirements can be large. Despite this, 27% of patients in the Hoorn et al study9 who developed hyponatremia received "recommended maintenance" fluids.
What Hatherill et al fail to consider is that hyponatremia results from an impaired ability to excrete free water due to antidiuretic hormone (ADH) excess and not from an impaired ability to handle sodium. There are 2 major reasons that a patient would have a stimulus for ADH excess resulting in impaired free-water excretion: (1) a hemodynamic stimulus such as volume depletion or (2) a nonhemodynamic stimulus such as syndrome of inappropriate ADH secretion. In either case, whether it is volume depletion or syndrome of inappropriate ADH secretion, the most appropriate fluid would be 0.9% NaCl. There is no rationale for the routine administration of hypotonic maintenance fluids to hospitalized patients that may have impaired free-water excretion caused by ADH excess. Hypotonic fluids should not be administered unless there is a free-water deficit or ongoing free-water losses. Even in edematous states such as nephrosis, cirrhosis, congestive heart failure, or acute glomerulonephritis, a case could be made to use 0.9% NaCl at a restricted volume, because these patients are at high risk for developing hyponatremia.
What is clear from the literature is that the practice of prescribing maintenance hypotonic fluids as recommended by Holliday and Segar10 is unsafe and places children at risk for fatal hyponatremic encephalopathy. NaCl (0.9%), on the other hand, has been used extensively in surgical patients and has never been associated with neurologic morbidity in the nonneurosurgical patient. The continued use of routine maintenance hypotonic fluids cannot be justified given the inherent neurologic risks. The administration of maintenance 0.9% NaCl is the most physiologic approach to preventing a disorder in both tonicity and hydration. It must be kept in mind that no one fluid rate or composition is suitable for all patients, and the administration of any intravenous fluid should be considered an invasive procedure, requiring close monitoring.
REFERENCES
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This article has been cited by other articles:
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  D. Bohn, E. Hoorn, and M. L Halperin Hospital-Acquired Hyponatremia Is Associated With Excessive Administration of Intravenous Maintenance Fluid: In Reply Pediatrics, December 1, 2004; 114(6): 1744 - 1745. [Full Text] [PDF]
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