Phosphorus Supply in the Parenteral Nutrition of Preterm Infants: A Survey in Four European Countries

Introduction: The amount of mineral intake required by very preterm infants to promote adequate health is still a matter of debate. Bonsante et al (PLOS One 2013) have recently proposed a method for estimating the parenteral phosphorus (P) requirement of preterm infants. This calculation takes into consideration the estimated ratio of Ca and P in bone mass, the ratio of nitrogen and P in the rapid growing cells, the minimal amino acid (AA) intake to obtain a positive nitrogen balance, and the AA retention. The aim of this study was to assess the P supply during parenteral nutrition (PN) of preterm infants in four European countries and to compare the current P parenteral intake with the requirements as determined by Bonsante et al.

Materials and Methods: An interactive, case-based questionnaire was used to determine the current routine practices of physicians from four European countries. Physicians were presented a web-based scenario of 28 weeks’ gestation infant requiring exclusive PN from birth onward ([Table 1]). They were then asked to prescribe PN for this patient for the first, second, and third days of life, and for the growing phase assuming that enteral feeding could not be tolerated. For each day of life, ranges with six plausible intakes and a “do not know” response were offered so that physicians could choose the most appropriate range of intake for each nutrient. To compare the observed parenteral P supply versus the actual needs, the parenteral P requirements were estimated by using the formula (P need = Ca intake/2.15 + [AA intake − 1.3] × 0.8 × 12.3). Differences between the observed P supply and requirement were determined using a paired t-test.

Results: The survey was performed in 199 neonatal intensive care units (NICUs) from four European countries (55 from Germany, 45 from the UK, 49 from France, and 50 from Italy) which represent 74% of the NICUs of the four countries. The analyzed answers were 181 out of 199 questionnaires (91%). The observed values for P supply were consistently lower than the estimated P requirements. The differences between the requirements and the observed values increased with the postnatal age of the preterm infant (i.e., difference of 0.1, 0.3, 0.4, and 0.6 mmol/kg/d for first, second, third days of life, and for the growing phase, respectively). Overall, some 38 to 53% of the reported prescriptions of parenteral P were below the requirements depending on postnatal age. Moreover, the P deficit showed an increase with postnatal age and reached a mean value of 0.6 mmol/kg/d during the growing phase, which represents a daily P deficit of ~40% of the estimated needs. The observed Ca/P molar ratio during the growing phase was ~1.8 which is close to the current guidelines (i.e., Ca/P = 1.6) but far from the Ca/P molar ratio obtained by using the equation of Bonsante et al.

Conclusion: Our study describes the parenteral mineral intakes prescribed in routine practice, and shows that while adequate Ca is typically provided, the provision of P is frequently below the needs necessary to promote adequate cellular, bone growth, and normal metabolic functions. Clinicians should reassess the supplied P amounts by PN formulations and support further research aimed at better defining P intake levels.

Keywords: phosphorus supply, parenteral nutrition, mineral intake

Table 1 Parenteral supply of AA, Ca, and P (mean ± SD) prescribed to a very-low-birth-weight infants during the first, second, and third days of life and during the stable period of growth

	AA observed (g/kg/d)	Ca observed (mmol/kg/d)	P observed (mmol/kg/d)	P requirement (mmol/kg/d)	p (P observed vs. required)
1st day of life	0.8 ± 0.7	0.8 ± 0.8	0.2 ± 0.4	0.3 ± 0.6	0.052
2nd day of life	1.5 ± 0.9	1.2 ± 0.9	0.5 ± 0.5	0.8 ± 0.6	<0.0001
3rd day of life	2.1 ± 0.9	1.3 ± 0.9	0.7 ± 0.5	1.1 ± 0.6	<0.0001
Growing phase	2.9 ± 0.9	1.6 ± 1.0	0.9 ± 0.5	1.5 ± 0.7	<0.0001

Note: Phosphorus requirement was calculated for each prescription using an equation taking into account the amount of amino acids and calcium prescribed.

Abbreviations: AA, amino acid; Ca, calcium; P, phosphorus.