Review articleSelected principles of perinatal–neonatal glucose metabolism
Introduction
Relative to glucose metabolism, the neonate is considered to be in a transition between the complete dependence of the fetus and the complete independence of the adult. The neonate must become independent after birth, balancing between glucose deficiency and excess to maintain the euglycaemic state. Since the fetus makes no endogenous glucose in utero1and depends on his/her mother for continuous substrate delivery, there is an obvious contrast with the variable and intermittent exogenous intake orally that is the hallmark of the neonatal period and beyond. Maintenance of euglycaemia especially in the sick and/or low-birthweight neonate, is difficult. Maturation of neonatal homeostasis is influenced by the integrity of the specific pathways of intermediary metabolism important in glucose metabolism, as discussed recently.2The heterogeneity that is the hallmark of neonatal glucose metabolism is illustrated by the multiplicity of conditions producing or associated with neonatal hypo- and hyperglycaemia.3This reinforces the concept that the neonate is vulnerable to carbohydrate disequilibrium. This topic has been the subject of a number of recent reviews.4, 5
Section snippets
Euglycaemia in the neonatal period
A primary example of the heterogeneity that exists in our understanding of neonatal glucose metabolism is that there are no uniform standards accepted for specific limits of euglycaemia. The definitions of what constitute hypo- and hyperglycaemia are quite variable. It is well accepted that glucose is the major substrate of carbohydrate metabolism. At birth, the maternal supply of glucose to the neonate, by definition, ceases abruptly. While the neonatal plasma glucose concentration is usually
Hypoglycaemia in the neonatal period
Although there is a large literature that focuses on the subject of neonatal hypoglycaemia, this topic remains quite controversial.12Areas of disagreement involve definition, method/site of sampling, symptoms, significance of asymptomatic status, management and, finally, its effect on neurodevelopmental outcome.10, 13In effect, there are four possible approaches to the definition of hypoglycaemia in the neonate: statistical; clinical; neurophysiological and neurodevelopmental.
First, from a
Hyperglycemia in the neonatal period
The definition of hyperglycaemia remains equally unsettled.23However, a consensus exists that the range exceeds 6.9–8.3 mmol/l.24The pathophysiological basis for the presence of hyperglycaemia has been thoroughly discussed previously3and is summarized below.
As micropremies (i.e. neonates born weighing ≤1000 g) represent a significant percentage of the neonates cared for in the neonatal intensive care setting, glucose homeostasis was evaluated in a group of micropremies born over the period of 1
Evaluation of glucose metabolism in the neonatal period
Metabolic research in the human neonate is generally limited by several basic ethical constraints, as discussed in a recent review.25Firstly, the studies must be non-invasive or minimally so. Secondly, blood samples should be small, particularly those obtained from the very-low-birthweight neonate. Thirdly, given the limited direct access to most organ systems, the approaches used must allow extrapolation from the sampled data to metabolic processes occurring in otherwise inaccessible areas.
Evaluation of hepatic glucose production in the neonatal period
During kinetic studies utilizing stable isotopic methodology, glucose infusion, glucose absorbed from the gastrointestinal tract, glycogenolysis and gluconeogenesis may contribute collectively to the rate of glucose appearance in the metabolic pool (i.e. plasma). Only the latter two variablesreflect the endogenous rate of glucose production, primarily from the liver.
Measurement of the true rate of glucose production usually gives a good estimate of the glucose requirement of the body and the
Evaluation of glucose utilization in the neonatal period
It is important to recognize that glucose is utilized by a variety of organs/tissues that have different metabolic characteristics.41, 43Firstly, there are organs/tissues that utilize glucose independent of insulin (e.g. brain). Secondly, there are organs/tissues that increase their glucose utilization with increments in plasma glucose concentration independent of increments in plasma insulin concentration (e.g. liver, gut and erythrocytes). Thirdly, there are organs/tissues that depend on
Acknowledgements
Some of this work was supported by R01 27287, awarded to Dr Cowett by the NIH NICHD.
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2016, Clinical BiochemistryCitation Excerpt :If left untreated, neurological damage can occur, leading to seizures, loss of consciousness, permanent brain damage, or, in severe cases, death [1–3]. Moreover, hyperglycemia is also common in this population due to immature endocrine function early in life, and can result in increased serum osmolality leading to cell injury and altered cell glucose transport [4]. The American Academy of Pediatrics recommends blood glucose monitoring in both symptomatic-hypoglycemic infants, and asymptomatic infants with risk factors by using point-of-care testing (POCT) at the bedside [5].