MIAMI BEACH — Using physiologic insulin replacement strategies, physicians can manage glycemia throughout the perioperative period and optimize patient outcomes.
“We have a number of options to improve glycemic control … and a number of strategies for transitioning the patient after surgery,” Dr. Luigi F. Meneghini said during a meeting on perioperative medicine sponsored by the University of Miami. He explained how to use basal insulin, supplemental scale boluses, and/or prandial insulin during the preoperative, intraoperative, and postoperative periods.
Even surgical patients not diagnosed with diabetes can experience hyperglycemia and associated perioperative and postoperative risks, said Dr. Meneghini, director of clinical operations, division of endocrinology, diabetes and metabolism at the University of Miami.
Why is the perioperative period such a risky time for people with diabetes? Surgery and anesthesia can increase levels of stress hormones, epinephrine, cortisol, growth hormones, and inflammatory cytokines such as interleukin-6 and tumor necrosis factor-alpha. Also, general anesthesia, bypass surgery, sepsis, parenteral nutrition, and use of steroids can alter insulin resistance, decrease insulin secretion, and cause lipolysis and protein catabolism. “This all makes perioperative management of diabetes so much more difficult,” he said.
Perioperative glycemic control can be achieved through implementation of the following strategies before, during, or after surgery:
▸ Preoperatively. The goal is to stabilize glycemia, in many cases with subcutaneous insulin. However, if the patient has type 1 diabetes, continue basal insulin, “no questions asked,” Dr. Meneghini said.
Discontinue all oral agents prior to surgery, perform a finger-stick glucose test every 4-6 hours, and use a supplemental scale for additional insulin if blood glucose levels exceed target values.
“You will need some basal insulin replacement. Insulin needs are still there when you are fasting; you can give [basal insulin] to anyone whether they are NPO [nothing by mouth] or not,” Dr. Meneghini said.
The American Diabetes Association recommends a glycemic target of about 110 mg/dL to less than 140 mg/dL for critically ill patients. For patients who are not critically ill, fasting blood glucose levels of less than 126 mg/dL or random blood glucose levels less than 180-200 mg/dL are recommended (Diabetes Care 2008;31[suppl. 1]:S12-54).
Several preoperative factors should be checked, but at least do an ECG, basic metabolic panel (BMP), and hemoglobin A1c assay, Dr. Meneghini said. “The [Hb]A1c before surgery may be useful for assessing risk and to determine if preoperative glycemic control is adequate.”
▸ Intraoperatively. Intraoperative management depends on the length of the procedure, Dr. Meneghini said. “For a 1- to 2-hour surgery, you can probably continue preoperative glucose management orders.” However, for a longer or more complex surgery, switch to intravenous drip insulin, ideally before surgery in order to stabilize glucose. Physicians can use the Modified Markovitz Protocol (Endocr. Pract. 2002;8:10-8) to calculate glycemic control intraoperatively.
Intravenous regular insulin has a half-life of 7 minutes, and by half an hour there is no more on board, “which can be very handy,” Dr. Meneghini said. “This is why we usually go to [intravenous] regular insulin for the perioperative period or critical care.”
▸ Postoperatively. After surgery, transition patients from intravenous to subcutaneous insulin management, Dr. Meneghini advised. “And that is a tricky passage in many cases. … We need to deal with inconsistent PO intake, stress, infection, and increased insulin resistance.”
Ensure adequate basal insulin levels during the transition to subcutaneous insulin, especially in type 1 diabetes patients. Basal insulin replacement can start at any time, Dr. Meneghini said. “I recommend you start 24 hours prior to discontinuation of the [intravenous] insulin drip. This ensures adequate basal coverage during the transition.”
Replace insulin according to physiologic needs. Match the basal replacement to hepatic glucose output, for example. Also match the prandial glucose to carbohydrate intake, and correct hyperglycemia as needed using a supplemental scale.
Postoperative nutrition should be taken into account. For example, if a patient is receiving total parenteral nutrition, start 1 U of regular insulin subcutaneously per 10-15 g of dextrose in the bag, Dr. Meneghini said. If the patient is on continuous enteral feeding, administer regular insulin every 6 hours or a rapid-acting insulin analog every 4 hours. Also, start 1 U of subcutaneous insulin to cover every 10-15 g of carbohydrates. If the enteral feed is a bolus, start 1 U of insulin subcutaneous per 10-15 g of carbohydrates and inject 15-20 minutes prior to the bolus.
If the patient is eating, use regular insulin or an insulin analog (preferred to minimize stacking) to cover meals, Dr. Meneghini said. Start 1 U of insulin subcutaneously to cover 10-15 g of carbohydrates and use what he calls the “Miami 4/12 Rule,” whereby the basal insulin replacement dose is calculated by taking the patient's weight in kilograms and dividing it by 4 and the prandial coverage is calculated by dividing the patient's weight in kilograms by 12.