A 19-year-old college student is brought to the emergency department by his friends due to… — USMLE Step 2 CK

A $19$ -year-old college student is brought to the emergency department by his friends due to intractable vomiting, diffuse abdominal pain, and profound lethargy for the past two days. His friends note that he has been extremely thirsty and has been urinating frequently for the past three weeks. He has no known past medical history and takes no medications.

Vital signs are temperature $37.0^\circ$ C ( $98.6^\circ$ F), blood pressure $95/60$ mm Hg, pulse $125$ /min, and respiratory rate $28$ /min. Physical examination shows dry mucous membranes, decreased skin turgor, and deep, rapid respirations. The abdomen is diffusely tender without guarding or rebound.

Laboratory values are as follows:
Sodium: $136$ mEq/L
Potassium: $5.1$ mEq/L
Chloride: $98$ mEq/L
Bicarbonate: $10$ mEq/L
Blood glucose: $520$ mg/dL
Blood urea nitrogen: $32$ mg/dL
Creatinine: $1.4$ mg/dL
Leukocyte count: $16,500$ /mm $^3$

Arterial blood gas (room air):
$pH$ : $7.24$
$PaCO_2$ : $23$ mm Hg
$PaO_2$ : $96$ mm Hg

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

A
Endotracheal intubation and mechanical ventilation
B
Intravenous sodium bicarbonate administration
Intravenous fluid resuscitation and continuous insulin infusionCevap
D
Intravenous piperacillin-tazobactam administration
E
Noninvasive positive-pressure ventilation

Cevap

Intravenous fluid resuscitation and continuous insulin infusion

The correct answer is intravenous fluid resuscitation and continuous insulin infusion. This patient is presenting with classic signs of diabetic ketoacidosis (DKA), including polyuria, polydipsia, abdominal pain, and an elevated anion gap metabolic acidosis. The deep, rapid breathing pattern (Kussmaul respirations) is a physiological compensation to blow off carbon dioxide and raise the blood pH. Using Winter's formula [

Expected \ PaCO_2 = (1.5 \times HCO_3^-) + 8 \pm 2

], the expected

PaCO_2

(1.5 \times 10) + 8 = 23

mm Hg. Because the patient's actual

PaCO_2

(

23

mm Hg) perfectly matches the expected value, there is no primary respiratory disorder, and the respiratory drive is fully intact. Therefore, no respiratory intervention is needed, and treatment should focus entirely on aggressive volume resuscitation and intravenous insulin to halt ketone production.

Adım Adım Çözüm

Calculate the anion gap to identify the primary acid-base disturbance.

Anion gap =

136 - 98 - 10 = 28

mEq/L.

Identifies the presence of a high anion gap metabolic acidosis, which in this clinical context is diagnostic of diabetic ketoacidosis.

Apply Winter's formula to determine if respiratory compensation is appropriate.

Expected \ PaCO_2 = (1.5 \times 10) + 8 = 23 \pm 2

mm Hg.

Differentiates between a purely compensatory respiratory response and a mixed acid-base disorder that might require respiratory intervention.

Compare the calculated expected carbon dioxide level with the patient's actual arterial value.

Actual

PaCO_2

23

mm Hg, perfectly matching the expected value.

Confirms the tachypnea (Kussmaul respirations) is purely compensatory; therefore, respiratory interventions like intubation are contraindicated.

Determine the primary treatment for the underlying metabolic derangement.

Select intravenous fluids and continuous insulin infusion.

Diabetic ketoacidosis management requires reversing the ketoacidosis and volume depletion without interfering with the body's compensatory respiratory drive.

Anahtar Kavram

Diabetic ketoacidosis typically presents with a high anion gap metabolic acidosis. Applying Winter's formula is essential to confirm that the associated tachypnea is an appropriate physiological compensation rather than impending respiratory failure requiring mechanical intervention.

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