A previously healthy 9-year-old boy is evaluated in the emergency department for a 24-hour… — USMLE Step 2 CK

A previously healthy $9$ -year-old boy is evaluated in the emergency department for a $24$ -hour history of severe abdominal pain, intractable vomiting, and progressive somnolence. His parents report that he has been drinking an unusual amount of water and waking up multiple times at night to urinate over the past month. He has lost $3 \text{ kg}$ during this time. On presentation, he is lethargic but arousable. Respirations are deep and rapid at $32\text{/min}$ , heart rate is $135\text{/min}$ , and blood pressure is $95/60 \text{ mmHg}$ . His mucous membranes are markedly dry. Capillary refill is $3 \text{ seconds}$ .

Initial laboratory results:

Laboratory Test	Result
Serum sodium	$132 \text{ mEq/L}$
Serum potassium	$4.8 \text{ mEq/L}$
Serum chloride	$98 \text{ mEq/L}$
Serum bicarbonate	$10 \text{ mEq/L}$
Blood glucose	$520 \text{ mg/dL}$
Venous pH	$7.12$

He receives a $10 \text{ mL/kg}$ intravenous bolus of $0.9\%$ normal saline. A continuous intravenous insulin infusion and $0.45\%$ normal saline at maintenance rates are initiated.

Three hours later, the patient is awake, alert, and reports feeling hungry. His heart rate is

98\text{/min}

, and blood pressure is

105/70 \text{ mmHg}

. Repeat laboratory studies show:

Laboratory Test	Result
Serum bicarbonate	$13 \text{ mEq/L}$
Blood glucose	$230 \text{ mg/dL}$
Venous pH	$7.21$

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

Add dextrose to the current intravenous fluidsAnswer
B
Transition from intravenous to subcutaneous insulin
C
Administer intravenous sodium bicarbonate
D
Decrease the rate of the continuous insulin infusion
E
Administer a second bolus of $0.9\%$ normal saline

Answer

Add dextrose to the current intravenous fluids

The most appropriate next step is to add dextrose to the intravenous fluids. In the management of pediatric diabetic ketoacidosis (DKA), continuous intravenous insulin is required to suppress lipolysis, halt ketogenesis, and resolve the metabolic acidosis. Acidosis resolution is typically defined by an anion gap

\leq 12 \text{ mEq/L}

, a venous pH

> 7.30

, and a serum bicarbonate

\geq 15 \text{ mEq/L}

. This patient's repeat pH of

7.21

and bicarbonate of

13 \text{ mEq/L}

demonstrate ongoing ketoacidosis, meaning the insulin infusion must continue. However, because blood glucose drops faster than ketone clearance, glucose levels frequently fall below

250 \text{ mg/dL}

before the acidosis resolves. To prevent iatrogenic hypoglycemia while allowing the insulin drip to continue clearing ketones,

5\%

10\%

dextrose must be added to the intravenous maintenance fluids.

Step-by-Step Solution

Identify the initial clinical diagnosis.

The patient presented with classic symptoms of new-onset Type 1 Diabetes Mellitus complicated by Diabetic Ketoacidosis (DKA), confirmed by hyperglycemia, acidosis (pH

7.12

), and low bicarbonate.

Establishing the baseline severity of DKA dictates the initial fluid and insulin management.

Evaluate the patient's repeat laboratory results and clinical status after 3 hours of therapy.

The blood glucose has fallen to

230 \text{ mg/dL}

(below the

250 \text{ mg/dL}

threshold), but the venous pH remains

7.21

and bicarbonate is

13 \text{ mEq/L}

. The patient is hemodynamically stable.

It is critical to distinguish between the resolution of hyperglycemia and the resolution of ketoacidosis.

Determine the necessary adjustment to the intravenous fluids.

Dextrose must be added to the maintenance fluids.

Because the acidosis has not resolved, the insulin infusion cannot be stopped or decreased. Adding dextrose prevents hypoglycemia while allowing insulin to clear the remaining ketones.

Key Concept

In pediatric diabetic ketoacidosis, when blood glucose falls below

250 \text{ mg/dL}

but anion gap acidosis persists, dextrose should be added to the intravenous fluids to allow continuation of the insulin infusion.

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