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 A 1c 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.