During an evening shift in the emergency department, a 71-year-old woman is evaluated for … — USMLE Step 2 CK

During an evening shift in the emergency department, a $71$ -year-old woman is evaluated for a three-day history of progressively worsening dyspnea and increased production of thick, yellowish-green sputum. She has a history of severe chronic obstructive pulmonary disease (COPD), essential hypertension, and osteoarthritis. Her current maintenance medications include a long-acting muscarinic antagonist, a long-acting beta-agonist, and as-needed albuterol.

Vital signs reveal a temperature of $37.6^\circ C$ ( $99.7^\circ F$ ), heart rate of $118/min$ , respiratory rate of $28/min$ , and blood pressure of $142/85 \text{ mm Hg}$ . Oxygen saturation is $86\%$ on room air.

On physical examination, she is in acute respiratory distress and is utilizing accessory muscles of respiration. Jugular venous pressure is visibly elevated at $10 \text{ cm H}_2\text{O}$ . Lung auscultation demonstrates prolonged expiration, diffuse expiratory wheezing, and faint bibasilar crackles. She has $2+$ pitting edema in both lower extremities.

Laboratory studies are notable for:
Leukocyte count: $12,500/\mu L$
Brain natriuretic peptide (BNP): $210 \text{ pg/mL}$ (normal $<100 \text{ pg/mL}$ )
Thyroid-stimulating hormone (TSH): $1.4 \mu\text{U/mL}$ (normal $0.5-5.0 \mu\text{U/mL}$ )
Free T4: $0.5 \text{ ng/dL}$ (normal $0.9-1.7 \text{ ng/dL}$ )

Arterial blood gas on room air:
pH: $7.27$
PaO2: $56 \text{ mm Hg}$
PaCO2: $66 \text{ mm Hg}$
HCO3: $29 \text{ mEq/L}$

A chest radiograph shows hyperinflation with flattened diaphragms and enlarged central pulmonary arteries, without focal consolidation.

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

Trial of noninvasive positive pressure ventilationAnswer
B
Intravenous administration of furosemide
C
Intravenous administration of piperacillin-tazobactam
D
Intravenous administration of sodium bicarbonate
E
Initiation of oral levothyroxine

Answer

Trial of noninvasive positive pressure ventilation

The correct answer provides ventilatory support. This patient is experiencing a severe acute exacerbation of COPD complicated by acute-on-chronic hypercapnic respiratory failure, as evidenced by her significant acidemia (pH 7.27) and elevated PaCO2 (66 mm Hg). In patients with a COPD exacerbation, a pH <= 7.35 and/or PaCO2 >= 45 mm Hg is a strong indication for a trial of noninvasive positive pressure ventilation (NPPV). NPPV improves alveolar ventilation, reduces the work of the fatigued respiratory muscles, and significantly decreases both mortality and the need for endotracheal intubation.

Step-by-Step Solution

Analyze the clinical presentation.

The patient has cardinal symptoms of a COPD exacerbation (dyspnea, increased sputum volume, sputum purulence).

Identifying the primary clinical syndrome guides the diagnostic and therapeutic pathway.

Interpret the acid-base status.

The arterial blood gas reveals an acute-on-chronic respiratory acidosis with a pH of 7.27 and PaCO2 of 66 mm Hg.

The degree of acidemia dictates whether supportive care alone is sufficient or if ventilatory assistance is required.

Evaluate the cardiac and endocrine findings.

Elevated JVP, lower extremity edema, and mildly elevated BNP in a COPD patient indicate cor pulmonale. The low Free T4 with normal TSH indicates euthyroid sick syndrome.

These secondary findings serve as distractors and must be correctly identified as consequences of chronic lung disease and acute severe illness rather than primary pathologies requiring immediate targeted intervention.

Determine the priority management step.

A trial of noninvasive positive pressure ventilation (NPPV) is selected.

In an awake, cooperative patient with a COPD exacerbation and respiratory acidosis (pH <= 7.35), NPPV is the most appropriate immediate intervention to reduce the work of breathing, reverse respiratory acidosis, and decrease the need for endotracheal intubation.

Key Concept

Noninvasive positive pressure ventilation (NPPV) is the first-line intervention for patients with acute exacerbations of COPD who develop acute-on-chronic respiratory acidosis (pH <= 7.35) or clinical signs of respiratory muscle fatigue.

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