Mature human breast milk is normally low in sodium. This protects against the development of hypernatremia in breast-fed neonates. Studies of the electrolyte composition of breast milk have shown a mean sodium value of 64.8 ± 4.4 mEq/L after delivery, dropping to a mean of 21.4 ± 2.3 mEq/L by the third postpartum day (colostrum), and leveling off to a value of 7 ± 2 mEq/L by 2 weeks (mature milk). Compared with cow's milk, mature human milk contains considerably less sodium, potassium, and chloride. Also, as the sodium concentration drops, the lactose level increases. Sodium chloride and lactose concentrations combine reciprocally to maintain the milk's osmolality at a level similar to that of blood. Any fall in lactose concentration could cause a rise in the sodium content of the milk.
The drop in sodium concentration is not dilutional, as the major decline in sodium concentration occurs approximately 1 day before the major increase in milk volume. Sodium concentration does not vary from foremilk to hind milk, suggesting that there is no alteration during storage in ductal structures. Allen et al showed that the correlation between lactose levels and sodium, chloride, and potassium levels during pregnancy provides evidence that paracellular pathways between mammary alveolar cells are open during pregnancy and are at least partially closed during lactation. Failure of these paracellular pathways to close might be one mechanism involved in elevated breast milk sodium content and lactation failure, but this mechanism has not been studied.
High levels of sodium in breast milk are closely associated with lactation failure. One study showed that those who failed lactation had higher initial breast milk sodium concentrations, and the longer they stayed elevated, the lower the success rate. This association has subsequently been confirmed. Several possibilities have been suggested as to the cause of increased sodium levels in breast milk. Delayed maturation, perhaps caused by inadequate levels of lactose is one possibility. It has been shown that sodium values are not affected by the mother's diet by the method of milk expression. One study looked specifically at the effects of maternal sodium intake on postprandial sodium concentrations in breast milk and showed no meaningful impact.
Reduction in feeding frequency is associated with a marked rise in milk sodium concentrations. This association might be related to reduced production, which could in turn be secondary to neonatal factors, such as primary suckling deficiency or poor suckling as a result of infection, or to maternal factors, such as stress, mastitis, or sore or retracted nipples. A vicious circle can develop so that when breast milk production is reduced, the infant becomes weak and sucks poorly, and the drive for lactation drops further until dehydration occurs.[8,12]
Breast milk sodium concentration is of particular physiologic importance in the feeding of neonates, and clinical problems arise if there is an excessive newborn intake of sodium. The kidney of the neonate has a limited capacity to concentrate solids, and the renal solute load, which is determined by sodium, potassium, chloride, phosphorous, and protein, exerts a major effect on water balance. This process can lead to a smaller margin of safety against dehydration, which is particularly a problem with diarrhea, fever, and low water intake. In hypernatremic dehydration, the extracellular fluid volume and plasma volumes are relatively preserved. The typical signs of dehydration, such as decreased skin turgor, tachycardia, and hypotension, are less pronounced than in hyponatremic or isonatremic dehydration. For these infants, the combination of inadequate fluid intake and hyperosmolarity is particularly devastating. Complications reported include convulsions, hyperglycemia, focal neurologic deficits, and disseminated intravascular coagulation.
The infant with hypernatremic dehydration secondary to breast-feeding is typically encountered somewhere between the first and third weeks of life. The infants are often strikingly lethargic, malnourished, and dehydrated. Gestation, delivery, and initial neonatal course are usually uncomplicated. The mother is often primigravid, intelligent, and well motivated to breast-feed. The infant is often described as a sleepy or quiet baby who does not appear hungry, and he or she usually thrives with adequate nutritional support.[2,4,9,12] A specific danger lies in the possible delayed recognition of this disorder, because most of the infants reported have nursed well and appear content. They therefore come to medical attention late, with severe dehydration, often weighing much less than 10% below birth weight.
Prevention of hypernatremic dehydration secondary to lactation failure requires the physician to be alert to this possibility as well as adequate instruction to the parents regarding the signs and symptoms of feeding difficulties. Lactation counseling should begin at the hospital and continue in the physician's office for at least 2 weeks after discharge. Encouraging mothers to pump their breasts to facilitate maturation might help. Scheduling a weight check for the infant within the first week after discharge might also be prudent and could in the long run result in both cost savings and health care advantages.
J Am Board Fam Med. 2001;14(2) © 2001 American Board of Family Medicine
Cite this: Neonatal Hypernatremic Dehydration Secondary to Lactation Failure - Medscape - Mar 01, 2001.