Hyponatremic, vomiting, and failing to thrive: An infant cast onto a sea of troubles

DR. MEDDINGS is a resident in internal medicine and pediatrics at The Ohio State University Medical Center and Columbus Children's Hospital, Columbus, Ohio.

DR. BATISKY is associate professor of clinical pediatrics and associate dean for admissions and records at The Ohio State University College of Medicine and Public Health, Columbus, Ohio, and medical director of the renal dialysis unit at Columbus Children's Hospital.

DR. GERMAK is associate professor of clinical pediatrics and chief of the division of endocrinology in the department of pediatrics, The Ohio State University College of Medicine and Public Health.

The authors and section editor have nothing to disclose in regard to affiliations with, or financial interests in, any organization that may have an interest in any part of this article.

Being on call for the hospital's pediatric general medicine and infectious disease services has kept you busy this morning, admitting children with dehydration from gastroenteritis and initiating sepsis work-ups for febrile infants. And once again, your pager displays the emergency department number.

In the ED, the team reports that your next admission is a 6-month-old boy who has been vomiting. His name seems familiar.... That's it! About a month ago, you heard your colleagues discussing this child's case during an earlier admission-they were describing him as one who hadn't fared well in the game of "formula roulette." You don't know the details of how the formula had been changed, but you do remember that he was admitted then with vomiting, hyponatremia, and failure to thrive.

You look at the chart for background and one notation is prominent: A diet history that was taken at the prior visit to the ED a month ago revealed that the first-time parents, having grown frustrated with their baby's persistent vomiting, decided to feed him with their own formula of 1:1 cow's milk and water. A few days afterward, he was admitted, rehydrated with intravenous fluids, and started on commercial ready-to-feed, iron-fortified, milk-based infant formula. The vomiting ceased by the third day after admission and the sodium level improved by discharge. His parents were given explicit instructions not to dilute the premixed formula.

As you walk into the examining room, the young mother is playing with your babbling patient, who is nearly sitting independently (tripoding) and who appears to be the size of, roughly, a 2-month-old. The mother appears tired and is hunting through two of her bags for the baby's favorite toy; one bag appears to be a backpack containing heavy textbooks and the other is full of baby supplies, including the ready-to-feed formula.

When, you ask, did the vomiting begin? And what has been done so far to try to stop it? The mother explains that the baby has been seen at several different clinics-at first because of health insurance problems, later because she and her husband saw no improvement in his vomiting and poor growth. The vomiting began at about 3 months of age, while the baby was being breastfed; various physicians noted that he was "growing slowly." The vomiting is always postprandial, she explains, involves food only, and is never forceful. It is also nonbilious and nonbloody. The child's pediatrician encouraged the mother to continue breastfeeding because there was no blood in the stool to support a milk-protein allergy.

At-home empiric trials of ranitidine (Zantac) and metoclopramide (Reglan) were started for gastroesophageal reflux. The baby continued to vomit and was unable to keep down the medications. The parents decided to try a standard milk-based infant formula-in fact, they tried several brands. They returned to the clinic for the 4-month well-child visit with the baby still experiencing postprandial emesis and having poor weight gain.

Formula for trouble?

But the infant seemed to vomit even more when given a milk-based formula than when breastfed, so the pediatrician again entertained the idea of milk-protein allergy and switched the diet to, first, a soy-based formula and then to a protein hydrolysate-based formula. Plans were made for an outpatient upper gastrointestinal radiographic series and abdominal ultrasonography (US) to evaluate for reflux and anatomic abnormalities.

Because vomiting persisted even with hydrolysate-based formula, the parents decided, on the recommendation of a family member, to try the ill-advised diluted cow's milk diet you read about earlier. A few days before the scheduled radiographic studies, the infant began vomiting after every meal and was taken to the ED. He had by then been taking the diluted cow's milk for five days.

Once the baby was rehydrated and discharged, according to his mother, the vomiting restarted intermittently after about one week, and had become much worse in the past two days. She asserts that she has given him ready-to-feed formula only, three or four ounces every four hours, as well as homemade pureed baby food. She also comments that he seems more interested in eating food if it is salty, and that he tends to vomit less when table salt is added to each mouthful!

Now, fill in the blanks!