The glucose infusion rate should maintain euglycemia. Glucose intolerance, defined as inability to maintain euglycemia at glucose administration rates < 6 mg/kg/min, is a frequent problem in VLBW infants, and especially in ELBW infants. The plasma glucose concentration should be kept below 130 mg/dL. This hyperglycemia in ELBW infants may also occur in combination with nonoliguric hyperkalemia. As discussed later (Chapter 6), these co-morbidities may be prevented with the early use of TPN.
Endogenous glucose production is elevated in VLBW infants compared with term infants and adults. High glucose production rates are found in VLBW infants who received only glucose compared to those receiving glucose plus amino acids and/or lipids. Clinical experience with hyperglycemia suggests that administration of glucose alone does not always suppress glucose production in VLBW infants. It appears that persistent glucose production is the main cause of hyperglycemia and is fueled by ongoing proteolysis that is not suppressed by physiologic concentrations of insulin. In addition, abnormally low peripheral glucose utilization may also contribute to hyperglycemia. Therefore a 5% glucose concentration instead of the standard 10% concentration of glucose may have to be used in more immature ELBW infants (<750 g).
Glucose intolerance can limit delivery of energy to the infant to a fraction of the resting energy expenditure, resulting in negative energy balance. Several strategies are used to manage this early hyperglycemia in ELBW infants as well as to increase energy intake.
Decreasing glucose administration until hyperglycemia resolves (unless the hyperglycemia is so severe that this strategy would require infusion of a hypotonic solution).