A 9 day-old male infant presents to the emergency department (ED) with a history of poor feeding and decreased activity.He was born at term following an uneventful pregnancy by normal delivery without complications. His birthweight was 3,500 g and Apgar scores were 9 and 9 at 1 and 5 minutes, respectively. The physical examination in the delivery room and nursery revealed a healthy newborn, and the baby was discharged from the hospital at 48 hours after birth. According to the parents, he was exclusively breastfed on demand at home, and he did well until 7 days of age, when he was noted to have infrequent latching, poor suck, and diminished feeding time at the breast. The parents also noted that he was less active and alert. They went to the pediatrician’s office, where the pediatrician found the baby to be extremely dehydrated, with decreased responsiveness. The weight at the pediatrician’s office was 2,500 g. He was immediately referred to the ED.On arrival at the ED, his temperature is 97°F (36.1°C), pulse is 98 beats/min, and respiratory rate is 24 breaths/min. Blood pressure cannot be obtained. Physical examination reveals a very wasted and jaundiced baby who has sunken fontanelles, absent tears, dry mucous membranes, and capillary refill greater than 3 seconds. There is no chest deformity, he has fair air entry in the lungs, and results of his cardiac examination are normal. His abdomen is concave and soft with no palpable masses. The external genitalia are normal for a male. Neurologic examination reveals generalized hypotonia, decreased responsiveness to painful stimuli, poor suck, and weak Moro reflex.The baby is assessed to be in hypovolemic shock. Intravenous fluids are started immediately, with a normal saline bolus of 40 mL/kg, followed by 5% dextrose in half-normal saline at 1.5 times maintenance (maintenance is 100 mg/kg per day). Complete blood count reveals a white blood cell (WBC) count of 12.3×103/mcL (12.3×109/L) with 39% neutrophils, 1% bands, 51% lymphocytes; hemoglobin of 18.6 g/dL (186 g/L); and platelet count of 360×103/mcL (360×109/L). Serum electrolyte assessment shows: sodium 191 mEq/L (191 mmol/L), potassium 4.4 mEq/L (4.4 mmol/L), chloride 136 mEq/L (136 mmol/L), and bicarbonate 17 mEq/L (17 mmol/L). Blood urea nitrogen is more than 140 mg/dL (>392 mmol/L), and creatinine is 3.1 mg/dL (274 mcmol/L). Venous pH is 7.4, and serum osmolarity is 453 mOsm/kg (453 mmol/kg). Total bilirubin is 15.4 mg/dL (263.3 mcmol/L), with direct bilirubin of 1.3 mg/dL (22.2 mcmol/L), and liver enzymes are normal. Catheterized urine has a pH of 6.0, with a specific gravity 1.020, 100 protein, large blood, small bilirubin, negative nitrites, small leukocyte esterase, few bacteria, 0 to 5 WBCs/high-power field (hpf), 3 to 10 red blood cells (RBCs)/hpf, and many uric acid crystals. Cerebrospinal fluid (CSF) is blood-tinged, Gram stain is negative, and there are 225 WBCs/mm3 and 3,700 RBCs/mm3. The CSF protein is 129 mg/dL, and glucose is 73 mg/dL (4.1 mmol/L). Blood, urine, and CSF cultures are obtained. The baby is admitted to the pediatric intensive care unit for further management.Intravenous fluid therapy is continued to correct the infant’s severe dehydration and hypernatremia. The volume replacement is achieved over 48 hours with a fluid composition targeting a sodium decrease of 0.5 mEq/L every hour. Twelve hours after admission, the fluid is changed from 5% dextrose in half-normal saline to 5% dextrose in normal saline, and 24 hours later it is returned to 5% dextrose in half-normal saline. On the third day of admission, 5% dextrose in third-normal saline is provided, and on the fourth day, 5% dextrose in fifth-normal saline is administered. The serum sodium finally is corrected to 145 mEq/L (145 mmol/L) on the fifth day of admission. Urine electrolytes on admission include sodium of 110 mEq/L (110 mmol/L), potassium of 15 mEq/L (15 mmol/L), and chloride of 84 mEq/L (84 mmol/L). Oral feeding is attempted on the third day, but the baby vomits the expressed human milk as well as formula supplementation.The possibility of cerebral edema is considered, and head computed tomography without contrast is performed, which reveals a dense straight sinus suggestive of sinus vein thrombosis, with no evidence of intracranial hemorrhage or edema. Subsequently, magnetic resonance imaging (MRI) with venography is obtained. The study shows a gap in flow in the expected area of the vein of Galen, possibly indicative of thrombosis, although there is excellent demonstration of adjacent veins, basal veins of Rosenthal, and internal cerebral veins and straight sinus. In addition, signal hyperdensity is noted in the lateral thalami, putamina, and peri-rolandic cortex that might be due to ischemic changes.On the fourth day of admission, the patient begins to tolerate feedings, and intravenous fluids are decreased. Intravenous antibiotics, administered since the day of admission for possible bacterial infection (ampicillin, cefotaxime, acyclovir), are discontinued on the third day after admission because results of urine, blood, and CSF cultures and herpes simplex virus polymerase chain reaction are negative. While in the pediatric intensive care unit, the mother is asked to express human milk to quantify her milk production. On the day of admission, a total of two drops of milk are expressed. On the second day, her production increases to 1 mL and slowly increases after that. The cause of the baby’s hypernatremia is presumed to be dehydration due to lactation failure.After 5 days, the baby is discharged from the hospital, to have close follow-up with the pediatrician and the neurology service, after much education of the parents. The weight at discharge is 3,320 g. Emphasis is placed on breastfeeding techniques and supplementation with formula if not enough human milk is produced. At 1-month follow-up, the baby is doing well and has no intercurrent problems. He is thriving, and there is no evidence of neurologic sequelae. A repeat head MRI is scheduled in 6 weeks.This baby presented in hypovolemic shock associated with severe hypernatremia that is defined as a sodium concentration greater than 150 mEq/L (150 mmol/L). (1) Sodium is the most important cation in the extracellular fluid space, playing a principal role in determining extracellular osmolality and maintaining intravascular volume. Diet is the primary source of sodium in the body. In a healthy state, dietary sodium is absorbed throughout the gastrointestinal tract and excreted mainly in urine and sweat and minimally in stool. The kidneys are the primary organs in regulating sodium balance. High sodium concentration leads to increased plasma osmolality which, in turn, stimulates thirst and secretion of antidiuretic hormone (ADH) from the pituitary gland. Increased ADH acts on the kidneys and leads to renal conservation of water, thus returning the sodium concentration to normal. Furthermore, the renin-angiotensin-aldosterone system and intrarenal mechanisms modify sodium excretion by the kidneys and maintain serum sodium concentrations between 135 to 145 mEq/L (135 and 145 mmol/L). (1)Hypernatremia can develop because of excessive sodium intake, water deficit, or water and sodium deficits. Excessive sodium intake can result from iatrogenic causes, such as intravenous hypertonic saline administration or saline enemas, as well as improperly mixed formula or intentional salt poisoning. Hyperaldosteronism can lead to excessive sodium absorption from the kidneys. Water deficit may occur in children who have nephrogenic or central diabetes insipidus due to defects in renal water absorption. Preterm infants may have increased insensible losses such as those occurring as a result of radiant warmers and phototherapy and may develop hypernatremia unless hydrated appropriately. Inadequate fluid intake due to inadequate breastfeeding, child abuse or neglect, and lack of thirst (adipsia) also may present with hypernatremic dehydration. Both water and sodium deficits occur when there are excessive gastrointestinal losses from diarrhea, emesis/nasogastric suction, osmotic cathartics, cutaneous losses such as in burns and excessive sweating, and in renal losses such as those occurring in diuretic use, diabetes mellitus, and acute and chronic kidney diseases. (1)Lactation failure and breastfeeding dehydration (BFD) are unique problems of young infants that may result from low maternal human milk production, difficulty with human milk extraction, or insufficient daily human milk consumption. (2)(3) Insufficient human milk synthesis can be seen in mothers who have developmental hypoplastic breasts or reduced mammary glands because of breast surgery. Absence of breast growth during pregnancy associated with limited postpartum breast engorgement and production of colostrum as well as delay in initiating breastfeeding for more than 12 to 24 hours may cause inadequate human milk production. Various endocrinopathies, including pituitary dysfunction, need to be considered in mothers who do not have adequate milk supply. Human milk removal may be difficult for mothers who have incorrect positioning and latching techniques or inverted nipples. Infants experiencing feeding difficulties due to sucking, swallowing, and breathing disorders and infants who have facial or oral anatomic abnormalities, including retrognathia, tongue-tie, and cleft palate, may have decreased ability to achieve adequate human milk removal. Low daily human milk intake also may result from infrequent feedings, especially in sleepy or sick infants or infants of mothers who are depressed or fatigued. (2)BFD is seen frequently in breastfed infants who are 5 days to 6 weeks of age and who have had minimal or no formula supplementation. (3) The infants generally are described as a sleepy, quiet, or “good” babies born to primigravida mothers who have had uneventful deliveries following normal pregnancies. Frequently, the parents are unaware of the severity of the baby’s illness. (3) The presenting signs and symptoms of BFD develop due to loss of at least 10% or more of body weight and accompanying hypernatremia. Clinical manifestations include doughy skin, sunken fontanelle, dry mucous membranes, decreased capillary refill, and signs of central nervous system involvement such as irritability, weakness, and lethargy. Tachycardia may be present, depending on the degree of dehydration, because hypernatremia actually allows for relative preservation of intravascular volume, blood pressure, and urine output.Adverse neurologic sequelae are estimated to occur in less than 1% percent of neonates who have BFD. (4) Intracranial hemorrhage is the most severe consequence of hypernatremic dehydration. As hypernatremia worsens and extracellular osmolality increases, water moves out of the brain cells, decreasing its volume. This can result in tearing of the intracerebral and bridging veins as the brain separates from the skull and meninges, leading to subarachnoid, subdural, or parenchymal hemorrhages. Changes in mentation and seizures may occur. Seizures also may be seen during overly rapid correction of hypernatremia if serum sodium concentrations decrease precipitously. “Idiogenic osmoles” generated in the brain cells as an adaptive mechanism to hypernatremia may cause the intracellular osmolality to remain relatively higher than serum osmolality. This osmotic pressure difference favors water movement from serum into the brain cells, resulting in cerebral edema. Thrombotic complications such as stroke, dural sinus thrombosis, peripheral thrombosis, and renal vein thrombosis also may develop in infants who have severe hypernatremia. (3) These complications possibly result from an increased coagulability state seen in hypernatremia.Multiple cases of hypernatremia in breastfed infants, including fatalities, (3)(5) have been reported in the literature since 1979. (6)(7)(8) In 2002, Excobar and associates (4) conducted a retrospective case-control study to evaluate the incidence of hypernatremia in neonates requiring readmission to the hospital and their neurologic outcomes. They studied 51,383 neonates whose birthweights were greater than 2,000 g and gestational ages were at least 36 weeks. A total of 110 babies required readmission within 15 days of discharge due to dehydration and were found to have either more than 12% weight loss or serum sodium concentrations of 150 mEq/L (150 mmol/L) or greater. A retrospective chart review was performed and a phone call made at 24 to 36 months of age to assess the infants’ neurologic outcomes. Readmission for dehydration occurred in 2.1 per 1,000 live births. The risk factors among vaginal births were being born of a first-time mother, being exclusively breastfed, maternal age of at least 35 years, and gestational age of 39 weeks or younger (adjusted odds ratios 5.5, 11.2, 3.0, and 2.0, respectively). Among cesarean births, risk factors associated with dehydration were having a hospitalization length of stay less than 48 hours (odds ratio 14.8). Possible adverse neurologic outcomes at 24 to 36 months occurred in 1 of 110 cases and 12 of 400 controls (P=.3). The authors concluded that serious complications of dehydration were rare, and interventions to avoid dehydration should be directed to first-time mothers and exclusively breastfed babies. (4) In another study of 686 exclusively breastfed neonates, 53 (7.7%) had weight loss of at least 10% of the birthweight (range, 10% to 14.8%), and 19 of those (36%) had hypernatremia (defined as serum sodium concentration greater than 149 mEq/L [149 mmol/L]). (9) The 53 infants had a greater incidence of cesarean delivery (77% versus 36%, P<.001) and lower maternal educational level (high school and university degree obtained in 68% versus 81%, P<.05) than neonates whose weight loss was less than 10%. In addition, of the 53 babies who experienced a weight loss of greater than 10%, the mothers were less likely to have had previous experience with breastfeeding compared with mothers of babies who experienced less than 10% weight loss (P<.01).Correction of hypernatremia depends initially on the clinical status of the patient. Fluid resuscitation with normal saline boluses should be provided if the patient is in hypovolemic shock. Subsequently, hypernatremia should be corrected slowly with a fluid sodium concentration between one quarter-normal saline and half-normal saline over a minimum of 48 hours, aiming for a sodium decrease of 12 mEq/L every 24 hours or 0.5 mEq/L every hour to prevent neurologic complications. Serum sodium should be monitored frequently to allow for adjustment of fluid composition and infusion rate. The patient who develops seizures requires infusion of 3% saline. Dialysis rarely is needed, and correction of the underlying cause of hypernatremia, such as assuring adequate human milk and formula intake, is imperative.We practice pediatrics in an era in which many mothers are encouraged to breastfeed their infants exclusively despite inadequate milk production, and as physicians, we are responsible for encouraging breastfeeding while ensuring its successful outcome to prevent lactation failure. This case of BFD helps to illustrate the importance of early postpartum follow-up after discharge and close monitoring of the weight of exclusively breastfed neonates, as proposed by the Hospital Discharge Guidelines of the American Academy of Pediatrics. (10) Pediatricians should review the important aspects of successful breastfeeding and the reasons for lactation failure before discharge from the nursery.Please see Schwaderer AL, Schwartz GJ. Treating hypernatremic dehydration. Pediatr Rev. 2005;26:148–150.