Thickened Preterm Formulas Can Exceed AAP Concentration Limits

Common ready-to-eat formulas for babies born preterm can have osmolalities much higher than recommended when they are thickened or fortified.

The American Academy of Pediatrics has long recommended that the osmolality of infant feedings stay below 450 mOsm/kg, based on a human milk norms of approximately 300 mOsm/kg and evidence that higher osmolalities can result in gastrointestinal problems. Preterm infants may be at particular risk with more concentrated feeds

But a recent study from the Neonatal and Infant Feeding Disorders Program at Nationwide Children’s Hospital has found that common thickeners and additives can push premade preterm formulas well beyond the AAP’s osmolality threshold. Providers who use thickeners or fortifiers to promote growth or mitigate dysphagia, then, may be causing another set of complications.

“First, this adds to the evidence that thickeners should not be used in the preterm population,” says Sudarshan Jadcherla, MD, director of the Neonatal and Infant Feeding Disorders Program and senior author of the study. “Second, this shows we need to be more cautious when we use any additives in premade formula.”

The study, published in the Journal of Parenteral and Enteral Nutrition, measured the osmolality of two standard ready-made preterm formulas on their own, and then with the addition of thickeners or supplements. Similac NeoSure, 22 cal/oz formula, had a median baseline osmolality of 268 mOsm/kg, and Similac Special Care, 30 cal/oz formula, had a median baseline osmolality of 407 mOsm/kg. (Similac Special Care is also available in a 24 cal/oz formulation, but that was not tested as part of the study.)

The authors added oatmeal and rice thickeners in 0.5 teaspoon per ounce increments. Even at 3 teaspoons per ounce of thickeners, the 22-calorie formula stayed below the AAP limit. The 30-calorie formula, however, began to exceed the 450 mOsm/kg limit with just 0.5 teaspoon per ounce of either thickener. The 30-calorie formula approached 700 mOsm/kg with 3 teaspoons of oatmeal. The osmolality of formula thickened with rice rose somewhat less dramatically, but was still significantly higher that the AAP recommendation by the end of testing.

The authors also added a combination of supplements to the formulas, including vitamin D, ferrous sulfate, a multivitamin and saline. The multivitamin alone pushed the 30 calorie formula above the AAP threshold, as did various combinations of the supplements. The 22 calorie formula reached and exceeded the threshold with a combination of vitamin D, ferrous sulfate and saline, and a combination of the multivitamin and saline.

Preterm providers may cite a number of reasons for thickening or fortifying feeds, says Dr. Jadcherla, who is also the associate division chief of Neonatology at Nationwide Children’s and a professor of Pediatrics at The Ohio State University College of Medicine.

“There is a belief that these babies can’t handle larger volumes, so that calories and nutrients need to be concentrated in smaller volumes, or that they should be given less liquid because lung disease makes it difficult to clear liquid or because their kidneys can’t handle the volume,” he says. “While there may be some truth to all of these in limited circumstances, high osmolalities can actually trigger gastrointestinal problems.”

Clinicians may also feel that thickening or fortifying is helping treat or prevent reflux, says Erika Osborn, APRN, NNP-BC, Neonatal and Infant Feeding Disorders clinical supervisor and a co-author of the study. In fact, thickening and fortifying may be exacerbating the issue due to the higher osmolalities.

“There are a number of interventions we’d rather try before considering thickening, even for a term baby,” she says. “Modification of feeding posture, feeding frequency, flow rate, how medications are administered and others may all be effective.”

The authors also say the study points to a common, but often overlooked, piece of advice: providers and parents alike should always try to use formulas as they are intended to be used. Premade formulas usually shouldn’t have things added to them; powdered formulas should be mixed according to manufacturer or medical instruction.

Levy DS, Osborn E, Hasenstab KA, Nawaz S, Jadcherla SR. The effect of additives for reflux or dysphagia management on osmolality in ready-to-feed preterm formula: practice implications. Journal of Parenteral and Enteral Nutrition.  2018 July 10. [Epub ahead of print]