During moderate or major surgery, elderly Type 1 and Type 2 diabetic patients should receive insulin, intravenously even if preoperative diabetes control has been good. However, for Type 2 patients undergoing minor surgery, regular glucose monitoring only may be required if their control has been good. For those with poor control, intravenous insulin is appropriate.
During surgery the two options are either a combined infusion of glucose, potassium and insulin, or separate glucose/potassium and insulin infusions. In this context insulin is necessary to maintain good glycaemic control while preventing proteolysis and lipolysis, while glucose provides energy and prevents hypoglycaemia (Alberti 1991). When glucose is given as 100 mL of 5% dextrose per hour, short-acting insulin doses of 1.5-2.0 U/h are usually sufficient together with 10-20 mMol potassium chloride per litre of glucose. Perioperative glucose monitoring is essential. Because of the risks of separate infusions running at different rates, it is generally recommended that a single infusion of glucose, insulin and potassium be used in this context. Following surgery, patients should revert to their original diabetes treatment.
The advantages and disadvantages of some of the options for insulin treatment in elderly Type 2 diabetic patients are compared in Table 12.4.
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