A 28-year-old man with a history of type 1 diabetes mellitus is brought to the emergency d… — USMLE Step 3

A $28$ -year-old man with a history of type $1$ diabetes mellitus is brought to the emergency department complaining of severe nausea, vomiting, and diffuse abdominal pain for the past $24$ hours. He reports missing several doses of his basal insulin due to a recent gastrointestinal illness. Vital signs show a temperature of $37.1^\circ\text{C}$ ( $98.8^\circ\text{F}$ ), heart rate of $124$ /min, blood pressure of $96/58$ mmHg, and respiratory rate of $24$ /min with deep, rapid breaths. Laboratory studies reveal:

Serum glucose: $580$ mg/dL
Serum sodium: $134$ mEq/L
Serum potassium: $4.6$ mEq/L
Serum chloride: $98$ mEq/L
Serum bicarbonate: $12$ mEq/L
Arterial pH: $7.22$
Urinalysis: $3+$ ketones

Arrange the following pharmacologic interventions in the most appropriate chronological sequence for the management of this patient, from initial presentation to clinical resolution.

1Administration of a $1$ to $2$ L bolus of $0.9\%$ sodium chloride
2Initiation of a continuous intravenous regular insulin infusion
3Addition of $5\%$ dextrose to the intravenous fluid regimen
4Administration of subcutaneous basal insulin prior to stopping the intravenous insulin

Answer

The correct chronological sequence for the pharmacologic management of Diabetic Ketoacidosis (DKA) is: 1) Initial fluid resuscitation with 0.9% sodium chloride, 2) Initiation of continuous IV regular insulin, 3) Addition of 5% dextrose to IV fluids when glucose drops below 200 mg/dL, and 4) Overlap of subcutaneous basal insulin before discontinuing the IV insulin drip.

The management of DKA follows a strict physiologic logic: restore volume first (isotonic saline), halt ketone production safely (IV insulin after confirming adequate potassium), prevent hypoglycemia while continuing ketone clearance (adding dextrose), and finally transition safely to maintenance therapy (subcutaneous insulin overlap).

Step-by-Step Solution

Administer 0.9% NaCl bolus.

Restores intravascular volume and improves tissue perfusion.

Severe osmotic diuresis leads to profound dehydration; rehydration is the paramount priority and also helps lower blood glucose by increasing renal perfusion and glucose excretion.

Start IV regular insulin drip.

Halts ketogenesis and drives glucose intracellularly.

Insulin suppresses lipolysis and ketone production. It is initiated only after starting fluids and verifying potassium is not critically low (≥3.3 mEq/L) to prevent life-threatening hypokalemia.

Add 5% Dextrose (D5W) to intravenous fluids.

Maintains serum glucose between 150-200 mg/dL.

Blood glucose often normalizes before the anion gap closes. Adding dextrose allows for the continuous insulin infusion required to clear ketones without causing severe hypoglycemia.

Administer subcutaneous insulin and overlap with the IV drip.

Provides continuous basal insulin coverage.

Discontinuing the IV insulin abruptly without a 1-2 hour subcutaneous overlap can lead to rapid rebound DKA due to the short half-life of intravenous regular insulin.

Key Concept

Stepwise pharmacologic management of Diabetic Ketoacidosis (DKA)

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