An internal medicine ward nurse urgently pages the on-call physician to evaluate a 68-year… — USMLE Step 2 CK

An internal medicine ward nurse urgently pages the on-call physician to evaluate a $68$ -year-old man whose respiratory status has rapidly deteriorated over the past $30$ minutes. The patient was admitted two days ago for a non-ST-segment elevation myocardial infarction and has been managed medically. He now reports severe, suffocating shortness of breath.

Temperature is $37.1^\circ$ C ( $98.8^\circ$ F), blood pressure is $210/115$ mmHg, heart rate is $118$ /min, respiratory rate is $32$ /min, and oxygen saturation is $82\%$ on room air. Physical examination reveals a profoundly diaphoretic man sitting bolt upright and using accessory muscles of respiration. Auscultation of the lungs reveals diffuse, high-pitched expiratory wheezing and fine crackles extending to the mid-lung fields bilaterally. Cardiovascular examination demonstrates a regular tachycardia with a prominent $S_3$ gallop. Jugular venous distention is present up to the angle of the mandible while sitting.

Bedside arterial blood gas analysis on room air shows:
* pH: $7.15$
* $PaCO_2$ : $50$ mmHg
* $HCO_3^-$ : $17$ mEq/L
* $PaO_2$ : $50$ mmHg

Which of the following is the most appropriate initial step in the management of this patient?

A
Administration of an intravenous sodium bicarbonate infusion
B
Administration of intravenous methylprednisolone and continuous nebulized albuterol
Application of noninvasive positive pressure ventilation and initiation of intravenous nitroglycerinCevap
D
Administration of a 1000 mL intravenous fluid bolus and broad-spectrum antibiotics
E
Emergent transport to the radiology suite for computed tomography pulmonary angiography

Cevap

Application of noninvasive positive pressure ventilation and initiation of intravenous nitroglycerin

The correct answer is the application of noninvasive positive pressure ventilation (NPPV) and initiation of intravenous nitroglycerin. This patient is experiencing acute decompensated heart failure (ADHF) characterized by 'flash' pulmonary edema and an acute hypertensive emergency following a recent myocardial infarction. The sudden sympathetic surge increases peripheral vascular resistance (afterload), which the failing left ventricle cannot overcome, leading to rapid fluid transudation into the alveoli. This causes severe hypoxia, crackles, an

S_3

gallop, and peribronchial edema presenting as wheezing ('cardiac asthma'). The arterial blood gas demonstrates a severe mixed acid-base disorder: a high anion gap metabolic acidosis (likely lactic acidosis from tissue hypoxia/hypoperfusion) and a concurrent respiratory acidosis. Based on Winter's formula, the expected

PaCO_2

1.5 \times 17 + 8 = 33.5 \pm 2

mmHg. The measured

PaCO_2

50

mmHg indicates respiratory failure due to muscle fatigue. The most appropriate initial step is NPPV to rapidly improve oxygenation and decrease the work of breathing, combined with intravenous nitroglycerin to rapidly reduce afterload and preload.

Adım Adım Çözüm

Analyze the patient's presentation and vital signs.

The patient has severe hypertension (

210/115

mmHg), respiratory distress, hypoxia, an

S_3

gallop, JVD, and bilateral crackles with wheezes.

To establish the primary clinical syndrome, which is acute decompensated heart failure presenting as 'flash' pulmonary edema with cardiac asthma.

Interpret the arterial blood gas results using Winter's formula.

Expected

PaCO_2 = (1.5 \times 17) + 8 = 33.5 \pm 2

. Actual

PaCO_2

(

50

mmHg) is significantly higher than expected, indicating a superimposed primary respiratory acidosis alongside the metabolic acidosis.

To identify if the patient is adequately compensating or experiencing impending respiratory failure due to severe pulmonary edema.

Determine the optimal immediate intervention based on the diagnosis and severity.

The patient requires immediate afterload reduction and respiratory support.

Noninvasive positive pressure ventilation (NPPV) decreases the work of breathing and improves oxygenation, while IV nitroglycerin rapidly reduces the severe hypertension (afterload) driving the fluid transudation.

Anahtar Kavram

Management of acute decompensated heart failure (flash pulmonary edema) presenting with acute hypertension, mixed acid-base disorder, and cardiac asthma.

Soru

Cevap

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