# Systematic Review on Individualized Versus Standardized Parental Nutrition in Preterm Infants
## 1 Introduction  
Parenteral Nutrition (PN) is a lifesaving therapy for preterm infants. PN is indicated when oral or enteral nutrition is not possible, insufficient, or contraindicated in order to avoid undernutrition and related adverse consequences. The nutrient stores of very low birth weight (VLBW, birth weight <1500 g) and extremely low birth weight (ELBW, birth weight <1000 g) preterm infants are low. Bridging PN ensures adequate fluid intake and nutrient supply for weight gain and possibly neurodevelopmental long-term outcome. VLBW infants are vulnerable to postnatal growth failure because the gut is immature, and provision of nutrients is challenging. The evidence showing the beneficial effects of enhanced PN to VLBW infants is accumulating. Providing amino acids and energy immediately after birth with PN is a standard practice to promote positive nitrogen retention [1]. PN can be provided as a standard pre-specified formulation or individually prescribed solutions. Individual prescriptions for PN are ordered and prepared every 24-48 h. The main advantage of individually prescribed PN is that it is tailored to suit a specific patient, thereby assuring the best possible nutrition and biochemical control [2]. However, several limitations such as errors, stability issues and risk of infections have been reported [2]. Batch-produced standardized PN bags can be readily available as ward stocks in neonatal intensive care units, enabling initiation of early PN immediately after delivery of a premature infant. Moreover, standard PN solutions incorporate expert nutritional knowledge and support [2]. Both techniques have been employed. Based on a low level of evidence, limited randomized controlled trials (RCTs) and some retrospective observational studies, in 2018 the combined working group on pediatric parenteral nutrition of ESPGHAN, ESPEN, ESPR, and CSPEN conditionally recommended that standard PN solutions (SPN) should generally be used over individualized PN solutions (IPN) in the majority of pediatric and newborn patients, including VLBW premature infants [3]. This recommendation has recently been endorsed by the UK National Guideline Alliance [4]. In addition, the combined working group recommended that individually tailored PN solution should generally be used when the nutritional requirements cannot be met by the available range of standard PN formulations (i.e., in very sick and metabolically unstable patients such as those with abnormal fluid and electrolyte losses; and in infants and children requiring PN for prolonged periods such as those with short bowel syndrome [3]. This recommendation will always be valid. The optimal PN management, SPN or IPN, is still controversial. The provision of PN is highly complex, requiring high-quality pharmacy aseptic manufacturing services. The proposed practical benefits of SPN were as follows:  
* Improved patient safety (minimization of procedural incidents),
* Provision of higher early intakes of amino acids and glucose, and better calcium phosphate ratio during the first week of life [5; 6],
* Prevention of ordering and compounding errors--due to the complexity of the supply chain much of the variations in actual nutrient intake are unintended [7],
* Improved pharmaceutical control of the physicochemical stability and aseptic manufacturing [8] by large scale industrial production and
* Reduction in costs [9]. Variation in PN macronutrient intake (glucose, protein or lipid intake) also results from differences in nutritional policy [10] and use of central, in contrast to peripheral, venous catheters which enable the use of more concentrated PN solutions. PN is recognized as a high risk and complex treatment. There is a need to compare outcomes including adverse events (sepsis, due to a less complex aseptic preparation, and mortality), growth (including weight gain) and protein intake, particularly influential on growth, as a surrogate measure of all other PN components, where the evidence base is still incomplete and questioned.