HPE HPE 85 – Spring 2017 - Page 42

Practical therapeutics when more liberal volumes of fluid are available in the recovery phase. Sufficient non-protein calories, as carbohydrate and fat, must be provided to meet basal metabolic energy demands and to ensure growth and development. An unbalanced substrate supply can lead to a high risk of physiological consequences (steatosis, hyperglycaemia, liver dysfunction). Without adequate non-protein calories, the body uses protein for muscle, visceral protein, or protein from PN as a calorie source; conversely, excess calories with insufficient protein will be deposited as fat. For efficient protein anabolism, the energy to nitrogen ratio (kcals: 1g N ratio) should be less than 250 or 30–40kcals per gram of protein Minimum energy requirements in preterm infants will be met by providing 45–55kcals/kg/day (including protein) although 90–120kcals/kg/day will maximise protein accretion. 1 40 Protein requirements Protein (nitrogen) is needed for growth and the formation of new tissues and the synthesis of plasma proteins, enzymes and blood cells. The protein required by the human body is manufactured from 20 different amino acids. Some of the amino acids become ‘conditionally essential’ in premature infants due to immaturity of the metabolic pathways and include cysteine, taurine, glutamine, tyrosine and histidine. Metabolic acidosis was common in the 1980s when casein-based adult solutions were used for premature infants who lack the ability to synthesise or metabolise some of these non-essential amino acids, such as phenylalanine, and tyrosine, which could lead to neurotoxicity. The current solutions used in premature infants contain crystalline L-amino acids with a higher composition of branched chain amino acids (for example, isoleucine, leucine and valine) and a reduced amount of phenylalanine and tyrosine. The composition of the amino acid solutions are based on either breast milk or cord blood amino acid profiles. Branched chain amino acids produce greater rates of protein synthesis and accretion from amino acids. At birth, the supply of nutrients from the placenta rapidly ceases. The infant becomes dependent upon its own protein stores for protein catabolism. In extremely low birth weight infants who receive glucose alone, 1.2g/kg/day of protein or 1–2% of their endogenous body hospitalpharmacyeurope.com protein stores are lost per day therefore a catabolic state may be reached in the first few days’ post-natal life without an adequate supply of protein. This accounts for the negative nitrogen balance seen in premature infants upon discharge from the neonatal intensive care unit due to insufficient nutrition and protein intake. Neonates have a high rate of whole body protein synthesis and the aim is to promote a positive nitrogen balance and optimise growth and development without causing metabolic acidosis from infants, critically ill patients. Premature infants have relatively high requirements due to the large body proportions of metabolically active organs. The majority of the basal glucose requirement is required to maintain adequate energy for the brain. At birth, the placental supply of protein and glucose stops. Initially glucose is produced by glycogenolysis but due to limited glycogen stores, gluconeogenesis becomes the principal source of hepatic glucose production. The ability to convert glucose into glycogen “Parenteral nutrition should be initiated when normal metabolic and nutritional needs are not met by enteral feeding in patients with adequate intestinal function” excess protein intake. A high in