Aims Hyperosmolar infant feeds can cause osmotic diarrhoea and may be a risk factor for necrotising enterocolitis; osmolality of infant formula is therefore usually <400 mOsm/kg. However, in fluid restricted infants and those needing nutritional support, formula may be over concentrated or supplemented. The aim of this study was to determine the effect of these practices on osmolality.
Methods The laboratory osmometer (Advanced Instruments Inc, Model 2020) was used to measure the osmolality of infant milk formula. The effect of hyper-concentration and supplementation on osmolality was then determined using 3 and 7 different infant formula respectively. Osmolalities were measured in triplicate.
Results The effect of hyper-concentration was shown to be linear using Pepti junior at 12.8% (standard), 17% and 19% concentration as shown in figure 1. This linear relationship was also demonstrated with Enfamil AR (15%) and Neocate (21%).
Effect of hyper-concentration on the osmolality (mosm/kg) of Pepti Junior formula. R2=0.9988.
The effect of individual additives on osmolality was found to be similar for the 7 infant formula as shown in figure 2. All preparations of SMA high energy and 5 of the 12 preparations of Nutriprem 1 exceeded an osmolality of 400 mOsm/kg.
Effects of additives on the osmolality of infant formulas. The effects of adding Thick & Easy (T&E), Thixo-D (TD), Duocal (Duo), Calogen (Cal) and Maxijul (Maxi) to standard infant formulae (Std form) to the feed osmolality. All additives were added at a concentration of 2%.
Conclusion The effect of hyper-concentrating infant formula was shown to be linear, meaning the osmolality at different concentrations can be predicted accurately.
The hyper-concentrated infant formula that were measured in this study did not exceed 400 mOsm/kg, with the exception of 21% Neocate which would not be used in practice.
Some infant formula when supplemented exceeded an osmolality of 400 mOsm/kg; this should be considered in cases of feed intolerance.