Test your medicine knowledge with the MKSAP challenge, in partnership with the American College of Physicians.

A 68-year-old man is evaluated in the hospital for a right intertrochanteric fracture sustained in a mechanical fall. He reports right hip pain but no other symptoms. He has hypertension and type 2 diabetes mellitus and was in his usual state of health prior to the fall. He checks his blood glucose level several times daily; his average blood glucose level is 150 mg/dL (8.3 mmol/L), with a low of 92 mg/dL (5.1 mmol/L) and a high of 208 mg/dL (11.5 mmol/L). Surgical repair is scheduled for tomorrow at 7 a.m. with an anticipated length of surgery of 1.5 hours; use of spinal anesthesia is planned. Medications are enalapril; extended-release metformin; insulin glargine, 20 units nightly; and insulin lispro, 8 units with each meal. It is 8 p.m., and the patient took his usual morning medications and insulin lispro prior to dinner but has not yet taken insulin glargine.

On physical examination, vital signs are normal. An ecchymosis is noted over the right hip. The right leg is externally rotated. The remainder of the examination is unremarkable.

Laboratory studies are significant for an HbA1c level of 8.2% and a plasma glucose level of 182 mg/dL (10.1 mmol/L).

In addition to discontinuing metformin, which of the following is the most appropriate preoperative diabetic management for this patient?

A: Administer insulin glargine as usual; withhold scheduled insulin lispro
B: Continue both insulin glargine and insulin lispro uninterrupted
C: Stop insulin glargine and insulin lispro; start intravenous insulin infusion
D: No further insulin until after surgery

MKSAP Answer and Critique

The correct answer is A. Administer insulin glargine as usual; withhold scheduled insulin lispro.

The most appropriate management of this patient’s insulin prior to surgery is to administer insulin glargine as usual and withhold the scheduled insulin lispro. Preoperative management of diabetes mellitus requires determination of the patient’s medical regimen, recent glycemic control, stress/duration of surgery, and anticipated duration of periprocedural fasting. In most cases, long-acting insulins (glargine and detemir) should be continued uninterrupted at the same dose unless a patient has risk factors for hypoglycemia or is undergoing a procedure requiring a prolonged period without enteral nutrition. Conversely, scheduled short-acting insulins such as lispro should be withheld during the fasting state because their purpose is to suppress postprandial hyperglycemia. In this case, the patient does not require a prolonged procedure or extended period of fasting. He also has no risk factors for hypoglycemia, and his average glucose level is higher than goal. Therefore, continuation of long-acting insulin while withholding scheduled short-acting insulin affords the best approach to glycemic control in the immediate perioperative period.

Continuing insulin lispro along with insulin glargine increases the risk for hypoglycemia during the fasting state. Short-acting insulins should be withheld when a patient is not taking anything by mouth unless the patient requires correction doses for significant hyperglycemia (plasma glucose level >200 mg/dL [11.1 mmol/L]).

Continuous insulin infusion is usually reserved for patients with uncontrolled hyperglycemia, with metabolic acidosis, or who are undergoing high-risk procedures (such as cardiac surgery). This patient has an acceptable plasma glucose level and is undergoing intermediate-risk surgery.

No insulin therapy increases the risk of significant hyperglycemia in this patient under physiologic stress. Therefore, treatment is indicated to prevent significant increases in the plasma glucose level.

Key Point

• Continuation of long-acting insulin while withholding scheduled short-acting insulin during fasting affords the best approach to glycemic control in the immediate perioperative period.

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