A 24-year-old man is evaluated in the intensive care unit 4 hours after admission for diab… — USMLE Step 3

A 24-year-old man is evaluated in the intensive care unit 4 hours after admission for diabetic ketoacidosis. He has a 10-year history of type 1 diabetes mellitus. On initial presentation to the emergency department, he was lethargic and reporting severe nausea and vomiting. His initial blood glucose was $680\text{ mg/dL}$ , and arterial blood gas showed a pH of $7.15$ . He was started on a continuous intravenous regular insulin infusion at $0.1\text{ units/kg/hr}$ and intravenous fluid resuscitation with 0.9% sodium chloride. His mental status has since improved, and he is now awake and alert.

Current vital signs are temperature $37.0^\circ\text{C}$ ( $98.6^\circ\text{F}$ ), blood pressure $118/76\text{ mmHg}$ , heart rate $92/\text{min}$ , and respiratory rate $18/\text{min}$ .

Laboratory results are as follows:

Parameter	Initial (Admission)	Current (4 hours later)
Serum glucose	$680\text{ mg/dL}$	$220\text{ mg/dL}$
Serum sodium	$132\text{ mEq/L}$	$138\text{ mEq/L}$
Serum potassium	$5.6\text{ mEq/L}$	$4.4\text{ mEq/L}$
Serum chloride	$98\text{ mEq/L}$	$106\text{ mEq/L}$
Serum bicarbonate	$10\text{ mEq/L}$	$14\text{ mEq/L}$

Which of the following is the most appropriate next step in management?

Continue the current insulin infusion and add 5% dextrose to the intravenous fluidsAnswer
B
Discontinue the insulin infusion and transition to subcutaneous insulin glargine
C
Decrease the insulin infusion rate by 50% and maintain the current intravenous fluids
D
Administer intravenous sodium bicarbonate and add potassium chloride to the intravenous fluids
E
Switch the intravenous fluids to 0.45% sodium chloride alone and continue the insulin infusion

Answer

The most appropriate next step is to continue the current insulin infusion and add 5% dextrose to the intravenous fluids.

The correct approach is to continue the insulin infusion and add 5% dextrose to the intravenous fluids. This patient's laboratory results demonstrate that his serum glucose has dropped below 250 mg/dL, but his anion gap remains elevated at 18 mEq/L (

138 - [106 + 14]

). Diabetic ketoacidosis (DKA) is considered resolved when the anion gap normalizes (typically

\leq 12\text{ mEq/L}

) and the serum bicarbonate is

> 15-18\text{ mEq/L}

. Because the anion gap is still elevated, the patient is still in DKA and requires continuous intravenous insulin to suppress lipolysis and ketogenesis. To prevent iatrogenic hypoglycemia while the insulin infusion is maintained, 5% dextrose must be added to the maintenance intravenous fluids.

Step-by-Step Solution

Calculate the current anion gap to determine if diabetic ketoacidosis (DKA) has resolved.

The current anion gap is calculated as Sodium - (Chloride + Bicarbonate) = 138 - (106 + 14) = 18 mEq/L.

Resolution of DKA is defined by the normalization of the anion gap (typically < 12 mEq/L) and bicarbonate levels, not by the normalization of blood glucose.

Evaluate the current serum glucose level in the context of the treatment protocol.

The serum glucose has fallen from 680 mg/dL to 220 mg/dL (now < 250 mg/dL).

When glucose drops below 200-250 mg/dL during DKA treatment, the risk of iatrogenic hypoglycemia increases significantly if insulin is continued without glucose supplementation.

Determine the appropriate fluid and insulin management step.

Dextrose (5%) must be added to the intravenous fluids while continuing the insulin infusion.

Insulin must be continued to suppress lipolysis and ketogenesis until the anion gap closes. Adding dextrose prevents hypoglycemia during this critical phase of ketoacidosis clearance.

Key Concept

In the management of diabetic ketoacidosis, when serum glucose falls below 200-250 mg/dL but the anion gap remains elevated, dextrose must be added to the intravenous fluids to allow the continuation of the insulin infusion for the clearance of ketones.

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