Chapter 64: Hyperglycemia

I. PROBLEM

The nurse reports an infant has a high blood glucose level of 240 mg/dL. Hyperglycemia is very common in premature low birthweight and extremely low birthweight infants and in extremely sick or stressed newborn infants. There is no universally accepted set definition of hyperglycemia in the newborn. An operational definition, a blood glucose level that triggers an osmotic diuresis, has yet to be defined by sufficient evidence. The treatment of hyperglycemia is also controversial. Following are some of the definitions used in the literature:

1. Whole blood glucose >120 to 125 mg/dL or a plasma glucose >145 to 150 mg/dL regardless of gestational or postnatal age or weight.

2. Whole blood glucose >125 mg/dL in term and >150 mg/dL in preterm infant.

3. Whole blood glucose >215 mg/dL (operational definition), proposed by Dr. Edmund Hey.

   A major concern with hyperglycemia is that it can cause hyperosmolality, osmotic diuresis, and subsequent dehydration. For every 18 mg/dL increase in plasma glucose, the plasma osmolality increases by 1 mOsm/L. In hyperglycemia, the high filtered load of glucose exceeds the amount the kidney tubules can reabsorb, and the excess glucose ends up in the urine. Because glucose is a solute, it draws water into the urine by osmosis (osmotic diuresis). Therefore, a high volume of glucose-containing urine is produced, which can lead to dehydration. It is difficult to know the exact level of blood glucose that triggers an osmotic diuresis in neonates. Significant osmolar changes have been reported to occur at a serum glucose >360 mg/dL.

   The other concern is that preterm infants with hyperglycemia are at an increased risk of mortality, infection, intracranial hemorrhage, neurodevelopmental impairment (prolonged or symptomatic hyperglycemia), white matter reduction on magnetic resonance imaging, retinopathy of prematurity, and developmental delay. Hyperglycemia is an independent risk factor for the prediction of death (57% likelihood of death when present in critically ill neonates). In the first 12 hours in asphyxiated term infants, it is associated with poor gross motor outcome, and if it occurs on the first day in infants undergoing therapeutic hypothermia for hypoxic ischemic encephalopathy, it is associated with a poor outcome. Hyperglycemia is common in infants with NEC and is associated with a poor outcome (increase in late mortality and longer NICU stay).

II. IMMEDIATE QUESTIONS

1. Are there any signs of hyperglycemia? Hyperglycemia is most common during the first week of birth, and most infants are asymptomatic or can have signs of an underlying disorder (eg, sepsis). Signs that are specific but unreliable in hyperglycemia include weight loss, fever, failure to thrive, glycosuria, metabolic acidosis, and dehydration secondary to an osmotic diuresis. Signs that are common in transient or permanent neonatal diabetes are glycosuria, ketosis, and metabolic acidosis.

2. What is the serum glucose value on plasma laboratory testing? Plasma glucose measurement by a laboratory performed method is the gold standard for measuring blood glucose levels. Point-of-care bedside ...