A variable-rate intravenous infusion of regular insulin is the safest and most versatile way to manage blood glucose levels during and after major surgery (Table 2). The safety of an intravenous infusion regimen has been demonstrated in the operating room, intensive care unit, and general surgical floor (2,9,11,42). The usual starting dose for a variable-rate insulin infusion is 1.0 U/h, with smaller starting doses recommended in patients with high insulin sensitivity (athletes and thin women). Higher starting doses of insulin (2.0-4.0 U/h) are recommended in patients with insulin resistance and to increase the time to metabolic decompensation should there be an interruption of insulin delivery (53). The majority of
TABLE 2 Variable-Rate, Intravenous Infusion of Regular Insulin_
Replace Chlorpropamide 5 days before surgery with short-acting sulphonylurea. Discontinue Metformin 48 h before procedures associated with renal dysfunction (risk for lactic acidosis).
Withhold oral hypoglycemic agent(s) the morning of surgery.
If non-emergent surgery, control BG prior to procedure (90 to 180 mg/dL).
Hold solid food for >8h (longer with history gastroparesis). Clear liquids permitted until 2h before surgery.
Antihypertensive and antianginal medication taken with water.
Measure fasting BG level with calibrated bedside glucose monitor.
Provide usual dose of intermediate-acting insulin at bedtime, the evening before surgery.
Insist upon early admission to hospital. Start intravenous infusion of 10% glucose in water or 0.45 N saline (510 g/h) around 7:00 am. Infuse isotonic saline solution if dehydrated due to bowel prep, prolonged fast, or osmotic diuresis.
Prepare an insulin solution that contains 250 Units short-acting (regular) insulin in 250 ml 0.9% saline (1 U/ml). Flush tubing with 50 ml insulin solution to minimize the effects of surface binding on insulin delivery.
Start intravenous infusion of insulin around 7:00 am using a separate calibrated pump. Choose an initial insulin infusion rate, typically 1.0 U/h. Insulin and glucose infusions may be piggy-backed into the same intravenous catheter.
Measure BG at least once every hour during and following major surgery.
Titrate variable-rate insulin infusion to hourly BG measurements, intravenous glucose infusion rate, and anticipated level of metabolic stress (Table 3).
Determine optimal glycemic range for individual patient. Maintain blood glucose levels in 90 to 180 mg/dL range for average control, and 90 to 110 mg/dL for tight control. Frequent BG monitoring and aggressive insulin titrations are required to avoid hypoglycemia.
Inject 15 to 25 ml 50% glucose solution for symptomatic hypoglycemia.
Measure electrolytes daily. Hyponatremia and hypokalemia are common in the postoperative period.
Measure urine for glucose and ketones when BG >200 mg/dL.
Convert variable-rate intravenous insulin regimen to a subcutaneous insulin regimen once the patient is tolerating solid food. Discontinue insulin infusion 30 to 60min after injecting subcutaneous insulin (Table 6).
Adjust subcutaneous insulin-dosage schedule and reinstitute oral hypoglycemic agent(s) doses prior to hospital discharge.
clinicians use a variable-rate insulin infusion and a fixed-rate glucose infusion. The rate of insulin delivery is typically adjusted once per hour (0.5-4.0 U/h increase or decrease) based upon frequent blood glucose measurements and an algorithm (Table 3). Recent protocols base each adjustment in the rate of insulin delivery upon the absolute BG value, the direction of BG change, and the amount of change from the previous BG measurement (5,7,11,54,55). An algorithm using a variable-rate glucose infusion has also been described (Table 4).
Watts etal. were able to achieve tight glucose control (mean glucose 136 - 15 mg/dL) with a low incidence of hypoglycemia using separate infusions of insulin and glucose. In contrast, patients managed with conventional therapy (subcutaneous sliding-scale insulin or fixed-rate insulin infusion) were not able to achieve near-normal BG control (mean glucose 208 - 20 mg/dL, 30-306 mg/dL range) (47).
In general, diabetic surgical patients require 0.3 to 0.4 Units of insulin per gram of infused glucose per hour (0.3-0.4 U g1/h1) (14,15,16,17). Higher doses of insulin are required for patients with pre-existing or acquired insulin resistance due to obesity, systemic infection, hypothermic cardiopulmonary bypass, certain anesthetics, elevated catecholamine levels, and steroid therapy. Patients with renal, hepatic, and heart failure may require decreased insulin doses (44,56).
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