2.9 Insulin Dose Adjustment
Even the most elaborate insulin treatment scheme (subcutaneous insulin infusion pump or multiple insulin injections) cannot mimic the subtle insulin adjustments of a healthy pancreas. The most common failing of insulin therapy, compared with natural secretion, is a lack of insulin in the minutes following the start of a meal and an excess of insulin 3-4 h after the meal. These faults can partly be avoided with pump treatment or with subcutaneous injections of a very short-acting insulin analogue (Iispro, asparte) combined with a split (divided into two or three injections during the day) basal insulin administration (see Chapter 6).
As insulin regimens and formulations differ widely from patient to patient, the strategies must be personalized. For low-intensity exercise lasting up to 1 h, and for any higher intensity exercise lasting less than 20 min, it is usually not necessary to change the insulin dose (Table 2.4). If the starting blood glucose is low or falling, it is wise to eat a snack before starting. Table 2.4 considers the insulins which are active during and after exercise.
The basic principles of treatment adaptations are similar to those applied with a multiple injection scheme.
One of the main advantages of pump treatment when exercising is the possibility of setting a temporary basal rate. Practically the exercising person reduces his or her basal rate by 20-50 per cent, sometimes up to 80 per cent, from 1 h prior to the beginning of the effort until several hours after the end of the exercise. For exercise lasting half a day or more, the reduced basal rate (80 per cent of 100 per cent) can be maintained for the whole following night.
If the meal insulin activity overlaps the exercising time, that insulin has to be decreased. The global amounts of insulin dose reduction can be estimated in accordance with Table 2.4. The decrease in meal insulin dosage is usually about 20-50 per cent.
As with a multiple injection scheme, there is a choice between ingesting more carbohydrate (usually 15-30 gh-1 exercise) or decreasing the insulin, or both. More details about the treatment adaptation during and after exercise for the pump patient are available in Wolpert.42
For efforts appearing in bold in Table 2.2, insulin dosage decrease is recommended. If the activity is scheduled during the 3 h after a meal covered by a short-acting insulin analogue, it is preferable to decrease the meal bolus by 10-50 per cent. If the exercise session begins during that period but lasts for more than 3 h, it is suggested that the basal rate be decreased temporarily from 20 min prior to the effort and up to 1-3 h after the end of it. It is highly recommended to start with short exercise sessions (30 min), increase the duration progressively and check the blood glucose before, during and immediately after.
Late basal rate decrease may be necessary during the night following an endurance exercise of several hours. The decrease is usually in the range of -10 to 20 per cent.
The Long-acting insulin analogues
Glargine and, to a lesser extent, its cousin detemir have a duration of action that makes subtle and short duration adjustments almost impossible. It is not possible, for example, to decrease the night insulin coverage by 10 per cent without also influencing the basal insulin dose of the entire next day. If the exercise session lasts a couple of hours, it is advised to act on the meal injections before and after the effort and to snack with regular blood glucose control during the effort. An alternative solution is to split the daily long-acting analogue dose into two injections (early morning and bedtime). This allows, to a certain extent, an adjustment of the basal insulin of the day and/or the night. Smaller doses have a shorter duration of action.
If taking a basal/bolus regimen, the lunch (prandial) short-acting insulin (analogue or classical) would need to be reduced by 10-50 per cent. If using a twice-daily regimen of soluble and intermediate insulin, the morning dose should not reduced because this would cause pre-lunch hyperglycemia. In this case the only recourse would be to take extra carbohydrate.
Decrease the short-acting insulin of the dinner injection (10-50 per cent) and basal night injection (10-20 per cent) for those on basal/bolus and the dinner soluble and intermediate insulins if on twice-daily injections.
Decrease the dinner bolus by 10-50 per cent and set the basal rate at 90 per cent from the beginning of the effort until 7:00 the next morning.
Slow swimming for 2h from 5.00 to 7.00 pm; dinner at 7.45 p.m.
Decrease the short-acting insulin of the dinner injection (5-10 per cent x 2 = 10-20 per cent) and basal insulin of the dinner or night injection (5-10 per cent x 2 = 10-20 per cent).
Hiking or skiing from 10.00 a.m. to 01.00 p.m. and from 2.00 p.m. to 4.00 p.m. (total 5h.)
Decrease the short-acting insulins of the lunch and dinner injections (25-50 per cent): and basal insulins of the morning and evening injections (25-50 per cent).
Have breakfast at 6:00 a.m. Decrease the lunch and dinner bolus by 25-50 per cent each. Set the basal rate at 60 per cent during the day and 80 per cent during the night until 7:00 a.m.
In all the examples, the insulin dosage adaptations must be combined with extra carbohydrate intakes and frequent blood glucose measurements.
We live in a society which battles cardiovascular diseases, which are, in large part the consequence of our lifestyles. Along with the decreased use of tobacco and healthier eating habits, regular physical exercise is of major importance for the improvement and maintenance of health.38 In addition, exercise is a source of pleasure and social contact for many people. It is therefore only natural that strategies have been developed which permit, and even encourage, those who have type 1 diabetes to devote themselves to the physical activity of their choice.
Before undertaking any exercise program we would advise patients to speak with their physicians and to have a general medical check-up, which should focus on the potential complications of diabetes, especially cardiovascular disease. This is even more important in those who have previously lived a sedentary lifestyle.
To be physically active, safe and confident, the diabetic person has to become familiar with certain basic rules, which we have tried to outline above. In order to learn the basic guidelines, and how to adjust one’s treatment to take part in sport, contact with a team of experienced professionals is a necessity. In addition, personal experience, together with frequent blood glucose checks, permits each person to adapt the general principles to his or her own personal situation. The diabetes associations and some specific groups (see www.diabetesport.org) offer publications, workshops and classes which provide opportunities for an education in sport and diabetes and for networking with others.
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