Background At the request of the intensive neonatal care unit, in order to give the babies less fluid, we replaced the usual amino acid mixture TPH 6% with Primene 10%. After this change however, a greater frequency of acidosis has been reported from data sourcing from arterial blood gases (ABG) analysis.
Purpose To thoroughly investigate the formulation of the two mixtures in order to understand if the cause of acidosis may lie in their different composition.
Materials and methods We analysed all ABG data, the compositions of the two products and determined pH and the buffering capacity: 2 ml of glucose 50% (the acid component of total parenteral nutrition) were progressively added to 50 ml of the two products.
Results 179 formulations containing Primene were prepared from August to November 2012 for 23 babies. We can identify three groups: 12 babies with birth weight >1500 g (A), 6 babies with birth weight 1000 – 1500 g (B1) and 5 babies with birth weight < 1000 g (B2). The ABG data collected were:
(A) pH 7.36, Base Excess (BE)-1.20, bicarbonate (HCO3) 23.5
(B1) pH 7.36, BE-2.46, HCO3 22.24
(B2) pH 7.29, BE-7.33, HCO3 18
The differences between groups B1/B2 were statistically significant (P < 0.0001). We pointed out that in TPH acetate ions are present which in vivo are bicarbonate precursors, responsible for alkaline reserve. Primene doesn’t contain acetate, but a greater amount of chloride ions and acid amino acids (glutamic and aspartic) and a smaller amount of basic amino acids (histidine and arginine). The measurement of the buffering capacity of the products showed the same trend of pH, pointing out a similar buffering capacity in vitro , despite a lower pH at the outset of Primene (5.23 against 5.66).
Conclusions We assume that the absence of acetate and the presence of chlorides can lead the formulations containing Primene to have a different buffering capacity in vivo favouring the observed acidosis. The statistical analysis of clinical data highlights a significant difference between newborns (B1) and (B2), which thus have a reduced tolerance to chloride ion loads. From our experience it is not advisable to use Primene in pre-term babies weighing <1000 g and it is also less attractive to use in the other groups, in which the water balance is less critical.
No conflict of interest.
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