Glucose in the operating room is a balancing act with an asymmetric downside. Run a little high and the harm is slow; let the patient drop and the harm is immediate and, under anesthesia, invisible. The whole job is staying in a sensible band, and it starts with picking the right tool.
The first decision: infusion or subcutaneous?
Reach for an insulin infusion when the case is demanding: a critically ill or unstable patient, glucose that stays above roughly 180 to 200 despite correction, surgery longer than about four hours, cardiac surgery, or anticipated swings in hemodynamics and temperature. For shorter, stable, ambulatory cases where the patient will eat soon, subcutaneous correction with regular glucose checks is enough. Current targets sit around 180 to 250 intraoperatively; the era of tight control has given way to avoiding hypoglycemia.
Running an insulin infusion
A common starting rate is the glucose divided by 100 in units per hour. Below the safe range you hold insulin and treat actively with dextrose, rechecking frequently; in the comfortable middle you hold and recheck on a longer interval; above it you run the calculated rate. From there you titrate to the trend, easing off when glucose is falling, holding steady when it is flat, and stepping up when it is climbing.
Subcutaneous correction and insulin sensitivity
Subcutaneous dosing only works if it is scaled to the patient. The same glucose warrants a different correction in a sensitive patient, older, low GFR, or newly suspected diabetes, than in a resistant one, high BMI, a large total daily dose, or on steroids. Classifying sensitivity first, then dosing by glucose band, is what keeps a sliding scale from being a guess.
The real danger is hypoglycemia
Whichever path you take, the floor matters more than the ceiling. An anesthetized patient cannot tell you they are crashing, so frequent monitoring and a low threshold to treat with dextrose are the safety net under the entire plan.
Where Master Anesthesia comes in
Master Anesthesia walks the whole pathway: the infusion-versus-subcutaneous decision, the infusion start rate with its hold-and-treat thresholds and trend-based titration, the sensitivity classification, and the subcutaneous correction scaled to it. See the Perioperative Insulin Calculator.