Perioperative management of diabetes: Translating evidence into practice
ABSTRACT
Glycemic control before, during, and after surgery reduces the risk of infectious complications; in critically ill surgical patients, intensive glycemic control may reduce mortality as well. The preoperative assessment is important in determining risk status and determining optimal management to avoid clinically significant hyper- or hypoglycemia. While patients with type 1 diabetes should receive insulin replacement at all times, regardless of nutritional status, those with type 2 diabetes may need to stop oral medications prior to surgery and might require insulin therapy to maintain blood glucose control. The glycemic target in the perioperative period needs to be clearly communicated so that proper insulin replacement, consisting of basal (long-acting), prandial (rapid-acting), and supplemental (rapid-acting) insulin can be implemented for optimal glycemic control. The postoperative transition to subcutaneous insulin, if needed, can begin 12 to 24 hours before discontinuing intravenous insulin, by reinitiation of basal insulin replacement. Basal/bolus insulin regimens are safer and more effective in hospitalized patients than supplemental-scale regular insulin.
KEY POINTS
- Surgery and anesthesia can induce hormonal and inflammatory stressors that increase the risk of complications in patients with diabetes.
- Elevated blood glucose levels are associated with worse outcomes in surgical patients, even among those not diagnosed with diabetes.
- The perioperative glycemic target in critically ill patients is 140 to 180 mg/dL. Evidence for a target in patients who are not critically ill is less robust, though fasting levels less than 140 mg/dL and random levels less than 180 mg/dL are appropriate.
- Postoperative nutrition-related insulin needs vary by nutrition type (parenteral or enteral), but ideally all regimens should incorporate a basal/bolus approach to insulin replacement.
DISCUSSION
Question from the audience: As an attending physician in a preoperative clinic I’m never sure what to do with NPH insulin the morning of surgery. What guidance can you give?
Dr. Meneghini: NPH is a peaking basal insulin, and the peak can induce hypoglycemia in a patient who is NPO. If we have the opportunity, we try to switch patients previously receiving insulin therapy to a long-acting basal insulin analog, which has a much flatter action profile and is safer in the fasting state. If there is no opportunity for switching, we instruct the patient to take two-thirds of his or her usual morning dose of insulin and we initiate a D5 drip when the patient arrives at the hospital.
Question from the audience: How do you handle perioperative insulin in patients on insulin pumps?
Dr. Meneghini: The pumps provide a subcutaneous basal insulin infusion, which should, if set correctly, maintain stable blood glucose levels when the patient is NPO. Supplemental doses of insulin to correct hyperglycemia can be delivered via the usual subcutaneous practice with a syringe or insulin pen. If you are uncomfortable with pump function, or if the pump insertion site interferes with the surgery site, simply replace the 24-hour basal amount delivered via pump with an injection of glargine or detemir divided into twice-daily injections. Correct hyperglycemia with supplemental-scale insulin as per usual protocol.
Question from the audience: The manufacturer of insulin glargine makes no recommendations for its use the night before or morning of surgery. What do you recommend?
Dr. Meneghini: It depends on whether the glargine is dosed appropriately. Most patients with type 2 diabetes require 0.4 to 0.6 U/kg/day of a long-acting insulin. If they’re on much more, they may be overdosed, and I would cut the basal dose by about half. Otherwise, 75% to 100% of the usual basal amount is appropriate. In type 1 diabetes, the usual replacement dose of basal insulin is 0.2 to 0.3 U/kg/day. If a patient is in this range, the basal insulin can be continued. Patients who experience hypoglycemia, or a substantial fall in blood glucose if meals are skipped or delayed, may be getting too much basal insulin and might benefit from a dose reduction when placed on NPO status.
Question from the audience: Metformin has a black-box warning advising that it be stopped at least 48 hours before surgery, but patients often come to surgery having taken metformin within the prior 12 to 24 hours. How should we manage such patients coming for elective surgery?
Dr. Meneghini: Metformin is cleared exclusively by the kidneys; its accumulation as a result of impaired kidney function (eg, due to hemodynamic instability or radiology studies using IV iodine) can result in increased lactic acid production by the liver and lactic acidosis. A patient who has taken metformin within the prior 48 hours but doesn’t have a risk of hemodynamic dysfunction is at low risk of lactic acidosis if hydrated appropriately. There’s not much choice if a patient needs urgent surgery and has recently taken metformin; in that case, just ensure maintenance of adequate glomerular filtration via fluid repletion to clear the drug.
Question from the audience: What’s the evidence for tight glycemic control or any type of glycemic control in patients undergoing outpatient surgery or “same-day” patients who will be admitted to a regular surgical floor? Also, what would you consider maximal glucose values for a patient going into elective surgery?
Dr. Meneghini: I haven’t seen any guidelines for glycemic control in patients undergoing outpatient surgery. If a patient has poor glycemic control coming into surgery, even for a minor procedure, the risk of an infectious complication may be increased. Keeping blood glucose below 180 mg/dL and avoiding electrolyte imbalances is likely sufficient in such patients. On the second question, if it’s an elective procedure and can be delayed a few hours, you can certainly institute IV insulin therapy to correct hyperglycemia rapidly—just ensure adequate replacement of fluids since the patient may have had volume depletion or dehydration as a result of the preceding osmotic diuresis. Once glycemic control is improved (blood glucose < 180–200 mg/dL), the patient can proceed to surgery.
Question from the audience: What are your recommendations for resuming oral diabetes medications after surgery?
Dr. Meneghini: Once patients are tolerating their meals and being considered for discharge, you may want to resume their oral medications, assuming their admission hemoglobin A1c levels were near goal. If glycemic control was inadequate preoperatively, this may be a good opportunity to adjust their prior regimen to more appropriate therapy. In some cases, this might include some form of insulin, either basal therapy or basal and supplemental insulin.
