Insulin Infusion

Figure 5.5 The difference between the counterregulatory responses expected between an insulin bolus (left) and insulin infusion (right). In the presence of continued insulin stimulus, counterreg-ulation can arrest but not correct glucose fall. The depth of the fall will depend upon insulin dose. Note the rebound above baseline on recovery in the left panel.

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Time at a dose of 0.1-0.2 mU/kg. Sampling for glucose and insulin is done at regular intervals thereafter for 90-120 minutes (Bloom et al. 1975). The rate of glucose fall, glucose nadir, rate of recovery and counterregulatory hormone responses can be determined. The rate of initial glucose decline has been used as a measure of insulin sensitivity, and where used for this purpose, the test can be terminated at 10 minutes, supposedly before counterregulation has occurred (Lazarus & Volk 1952). The rate of recovery can be taken as a measure of counterregulatory capacity. This model is very effective for inducing hypoglycaemia, but the nadir occurs very quickly and is uncontrolled and the counterregulatory response is correspondingly brisk. In contrast, clinical hypoglycaemia usually develops more gradually and is reversed more slowly. Therefore, a modification of this model was described in 1972 whereby insulin was infused intravenously at the rate of 0.04 units per kg per hour or subcutaneously over 12 hours (Carter et al. 1972). The resulting hypoglycaemia is more gradual and there are small but important differences in counterregulatory findings between the two methods.

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