Blood glucose monitoring

Regular blood glucose monitoring, coupled with activity and nutritional logs, is essential for developing insulin strategies to prevent hypo- and hyperglycemia. Prior to and during activity, measurements should be taken every 30 min to map glucose trends, as a single assessment will not determine the direction of change. Post-exercise monitoring can be less frequent (every 2 h) but is imperative to avoid late-onset hypoglycemia.

Patients and parents should be told that ‘body awareness’ and symptoms of hypo- or hyperglycemia do not translate to quantitative estimation of a child’s blood glucose levels. Indeed, a poor correlation exists between estimated and measured blood glucose in exercising youth with diabetes. Because frequent monitoring may be impractical in some sports, the convenience of continuous glucose-monitoring devices (e.g., Guardian RT, Medtronic) and insulin pump therapy may be ideal for youth.Insulin

Whether therapy is by continuous subcutaneous insulin infusion (CSII) or multiple daily injections (MDI), any adjustments made to an insulin regimen must be preceded by a history of self-monitoring and a log of blood glucose measurements. Specific modifications to insulin management depend on a combination of factors, including the type, duration, and intensity of exercise, as well as the child’s nutrient intake and level of fitness. Because it is impossible to predict the exact insulin reduction needed, individuals should use records of previous experiences as a guideline and always have additional carbohydrates available. The need for insulin is less during exercise, and reductions in basal/bolus needs may be as low as 10% for light activities (e.g., brisk walking) and as high as 90% for prolonged vigorous activities (e.g., marathon). Indeed, several elite athletes with diabetes will remove their insulin pump altogether for sport and competition to dramatically reduce circulating insulin levels.

Pump/CSII reductions

Quantitative adjustments for active children and adolescents wearing insulin pumps have yet to be established. A recent study demonstrated that when children maintain their usual basal insulin infusion rates during unplanned activity, performed several hours after a meal, they typically develop late-onset postexercise hypoglycemia during sleep, even though hypoglycemia does not typically occur during exercise. Furthermore, after complete removal of insulin delivery during exercise, 60% of children still had nocturnal hypoglycemia, as measured by a continuous glucose-monitoring system. The importance of reductions in bedtime basal rates and proper bedtime snacks is emphasized in such cases of intensive therapy and should be based on a history of glucose responses to physiological changes such as exercise, meals, and psychological stressors.

Basal Bolus/MDI reductions

On the basis of limited published studies with children, patients who are on MDI therapy often become hypoglycemic within 45 min of starting strenuous exercise when the activity is performed 2 h after a typical meal and their usual insulin. This reduction in blood glucose can be prevented by a 30-50% reduction in premeal bolus insulin. Exercise performed just after a meal may cause a greater risk of hypoglycemia because plasma insulin levels are elevated 2-3-fold. For more prolonged activities, a 50-90% reduction in insulin may be needed. Higher aerobic exercise intensities that are prolonged elicit a greater drop in blood glucose and a greater need for reduced insulin dosage. In contrast, exercise performed in the fasted or postabsorptive state (i.e., >3 h after insulin analog administration and meal) may be performed with no reduction in bolus insulin. Because muscular contractions accelerate insulin absorption, the site of injection should be distal from working muscles to minimize risk of hypoglycemia, and fast-acting carbohydrates should be made available to treat hypoglycemia.