Insulin Therapy in Diabetic Ketoacidosis
A 22-year-old man arrives in the emergency department with vomiting and drowsiness. Glucose is 28 mmol/L, arterial pH 7.10, bicarbonate 8 mmol/L, potassium 4.2 mmol/L, and urine ketones strongly positive. Blood pressure is 96/58 mm Hg and he is clinically dehydrated. After intravenous fluid resuscitation is started, how should insulin be administered?
- A.Subcutaneous sliding-scale regular insulin
- B.Subcutaneous long-acting insulin glargine alone
- C.Intramuscular injection of NPH insulin
- D.Continuous intravenous infusion of regular insulinCorrect
Explanation
Diabetic ketoacidosis requires a continuous intravenous infusion of regular (short-acting) insulin, typically 0.1 units/kg per hour, started after volume resuscitation has begun and once serum potassium is confirmed to be at least 3.3 mmol/L. The intravenous route is mandatory because peripheral vasoconstriction and dehydration make subcutaneous absorption erratic and unpredictable in a hypovolaemic, acidotic patient, and because the very short plasma half-life of intravenous insulin allows minute-to-minute titration and immediate reversal if hypoglycaemia or hypokalaemia develops. Insulin suppresses lipolysis and ketogenesis and restores peripheral glucose uptake, so closure of the anion gap and clearance of ketonaemia, not the glucose level alone, defines resolution. Insulin also drives potassium intracellularly, so potassium must be checked before starting and replaced during therapy; if it is below 3.3 mmol/L, insulin is withheld until it is corrected, otherwise life-threatening hypokalaemia and arrhythmia can follow. When glucose falls to about 11 to 14 mmol/L, dextrose is added to the fluids while the insulin infusion continues at a reduced rate until the acidosis clears. Long-acting and intermediate-acting insulins cannot be titrated and are unsuitable for acute management, although basal insulin is given subcutaneously one to two hours before the infusion is stopped to prevent rebound ketosis. Subcutaneous rapid-acting analogue protocols are an alternative only in mild, uncomplicated ketoacidosis in a monitored setting, not in a drowsy, hypotensive patient with a pH of 7.10.
Why each option
- A.
- Subcutaneous sliding-scale insulin is absorbed erratically in dehydrated, vasoconstricted patients and is reserved at most for mild uncomplicated cases.
- B.
- Long-acting glargine cannot be titrated and does not reliably shut off ketogenesis in an acutely acidotic patient.
- C.
- Intermediate-acting NPH given intramuscularly has unpredictable absorption and an unsuitable pharmacokinetic profile for acute ketoacidosis.
- D.
- Correct. A titratable continuous intravenous infusion of short-acting insulin is standard for diabetic ketoacidosis after fluids are started and potassium is checked.
Reference: American Diabetes Association Standards of Care in Diabetes, 2025
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