Gastrointestinal immune and microbiome changes during parenteral nutrition

Parenteral nutrition (PN) is a lifesaving therapy that provides intravenous nutrition support to patients who cannot, or should not, feed via the gastrointestinal (GI) tract. Unfortunately, PN also carries certain risks related to infection and metabolic complications compared with enteral nutrition. In this review, an overview of PN and GI immune and microbiome changes is provided. PN impacts the gut-associated lymphoid tissue functions, especially adaptive immune cells, changes the intestinal epithelium and chemical secretions, and significantly alters the intestinal microbiome. Collectively, these changes functionally result in increased susceptibility to infectious and injurious challenge. Since PN remains necessary in large numbers of patients, the search to improve outcomes by stimulating GI immune function during PN remains of interest. This review closes by describing recent advances in using enteric nervous system neuropeptides or microbially derived products during PN, which may improve GI parameters by maintaining immunity and physiology.

Theoretical Perspective: Resilience in Medically Fragile Adolescents

Medically fragile adolescents require medical technology and skilled care from parents and nurses in daily life. These adolescents may be ventilator dependent, require intravenous nutrition or medications, depend on nutritional or respiratory support, and depend on nursing care or other medical devices for daily living. Much of the extant research on medically fragile children and adolescents has lacked an overarching theoretical perspective. Findings suggest that peer relationships, family support, technology dependence, school attendance, and self-esteem are concepts of relevance for these adolescents. Thus, a theoretical framework derived from the risk and resilience literature was developed to identify the nature of their interrelationships using theory derivation techniques. The resilience in medically fragile adolescents framework was derived using concepts described by these adolescents. Further study is needed to test this model in medically fragile adolescents with hopes to foster positive outcomes for these adolescents.

Urinary citrulline in very low birth weight preterm infants receiving intravenous nutrition

As gut immaturity precludes full enteral feeding, very low birth weight (VLBW) preterm infants receive parenteral nutrition (PN) during the first few weeks of life. Weaning VLBW infants off PN, however, is a top priority since PN is associated with a high risk of complications. The decision making is purely empirical, as there is currently no suitable index of gastrointestinal (GI) maturity. Plasma citrulline concentration is considered an index of GI function in conditions such as short-bowel syndrome and coeliac disease in adults. To identify the factors determining urinary citrulline excretion, and determine whether urinary citrulline excretion could be used as a non-invasive index of GI tolerance to enteral feeding, nutritional intake and urinary citrulline were monitored bi-weekly in forty-seven preterm infants < 1500 g (interquartiles 880–1320 g), during their stay in the Neonatology unit. Median urinary citrulline was 24·7 μmol/mmol creatinine (14·5–38·6 μmol/mmol creatinine). No relationship was observed with the percentage of energy tolerated enterally. In multivariate regression analysis, weak correlations were found with post-conceptional age (P = 0·001), parenteral amino acid supply (P = 0·001) and the daily volume of enteral mixture administered (P = 0·043). A significant correlation was found with urinary nitrite+nitrate excretion (r0·47;P < 0·001). We conclude that in preterm infants: (1) one of the major determinants of urinary citrulline may be the biosynthesis of citrulline from arginine by NO-synthase; (2) urinary citrulline cannot be used to predict GI tolerance. This is consistent with the observations that, in neonatal gut, citrulline is converted to argininein siturather than exported towards the kidneys as observed in adults.