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Letters to the Editor

Indian Pediatrics 2002; 39:599-600

Hypernatremic Dehydration in a Neonate

 

I read the recent case report(1) on this subject with interest. The authors have discussed a neonate with breast-feed mal-nutrition related hypernatremia. Many features of the index case however do not fit into this entity and require clarifications:

1. Inadequate breast milk production is the most important factor in the pathogenesis of this entity(2) No comment has been made regarding the adequacy of milk production. Authors have mentioned that normal urine output, as in this case, could not be the only criteria for adequacy of breast-feeding and factors like weight loss and dehydration should also be valuated. As conditions like diabetes insipidus (DI) can also lead to weight loss and dehydration, these criteria cannot be a surrogate to inadequate breast milk production.

2. Hypernatremia in this case has been attributed to dehydration and thereby should have been associated with concentrated urine. How do authors explain extremely low urinary osmolality (61 mOsm/kg) and specific gravity (1005) in this case, a finding that excludes the diagnosis of dehydration due to decreased breast milk production?

3. Excessive weight loss, hypernatremia, elevated serum osmolality, normal urine output, dehydration and low urinary osmolality in this case strongly suggest the diagnosis of DI. The authors have mentioned that fluid deprivation test ruled out central and nephrogenic DI. A few points however require clarifications: (a) Serum osmolality decreased from 294 mOsm/kg to 290 mOsm/kg after fluid deprivation! How do the authors explain a decrease in serum osmolality (instead of an expected increase) after a period of fluid deprivation?; (b) Criteria for termination of water deprivation test include weight loss >5%, serum osmolality >300 mOsm/kg, serum sodium >150 mOsm/L or a urine osmolality >800 mOsm/L(3). In this case fluid deprivation was terminated prematurely (serum osmolality 290 mOsm/L). The authors state that normal urinary osmolality after fluid deprivation (320 mOsm/kg) and vasopressin administration (397 mOsm/kg) excluded DI. Contrary to these conclusions, these findings (urinary osmolality <800 mOsm/L after water deprivation and vasopressin administration) are suggestive of nephrogenic DI(4); and (c) There is marked discrepancy between measured (294 mOsm/kg) and calculated osmolality (466 mOsm/kg, as calculated from the laboratory data provided). What explanations do the authors offer?

4. Authors mention that the neonate went into shock after vasopressin injection (severe enough to require fluid boluses and dopamine). It is difficult to understand how vasopressin, a vasopressor, could have led to shock in the already dehydrated neonate. This point needs to be emphasized, as fluid deprivation is not only required but also potentially hazardous under such circumstances. Hypernatremia (Na >150 mEq/L) and elevated serum osmolality (>300 mEq/L) in the presence of low urine osmolaity (<400 mOsm/kg) are sufficient to diagnose DI and fluid deprivation is not required.

5. Breast milk sodium levels should be estimated in all breast fed neonates with hypernatremia as elevated breast milk sodium is an important factor contributing to hypernatremia(5). This also has implications in the decision of restarting breast-feeding, which should be initiated only when the breast milk sodium levels have become normal. Non-availability of breast milk sodium in this case thus poses limitations regarding diagnosis and management.

Anurag Bajpai,

Junior Resident,

Hostel No.7, Room No. 87,

Gents Hostel,

All India Institute of Medical Sciences,

New Delhi 110 029,

India.

.

 References


1. Bhat SR, Lewis P, Dinakar C. Hypernatremic dehydration in a Neonate. Indian Pediatr 2001; 38: 1174-1177.

2. Roddey OF, Martin ES, Swetenburg RL. Critical weight loss and malnutrition in breast-fed infants. Am J Dis Child 1981; 135: 597-599.

3. Hochberg Z, Rogol AD. Polyuria. In: Practical Algorithms in Pediatric Endocrinology, 1st edn. Ed. Hochberg Z. Basel, Karger, 1999; pp 52-53.

4. Coalco MP. Hormones and disorders of water and sodium homeostasis. In: Pediatric Endocrine Disorders, 1st edn. Eds. Desai MP, Bhatia VL, Menon PSN. Mumbai, Orient Longman, 2001; pp 289-300.

5. Anand SK, Sandborg CS, Robinson RG, Leiberman E. Neonatal hypernatremia associated with elevated sodium concentration of breast milk. J Pediatr 1980; 96: 66-68.

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