A daughter brings her 75-year-old father to the emergency department due to his profound s… — USMLE Step 2 CK

A daughter brings her 75-year-old father to the emergency department due to his profound sleepiness and labored breathing over the preceding 72 hours. The patient has developed a worsening cough productive of yellow sputum and subjective fevers during this time. His medical history includes chronic obstructive pulmonary disease (COPD), benign prostatic hyperplasia, and essential hypertension. His home medications are a tiotropium inhaler, as-needed albuterol, and amlodipine.

Vital signs show a temperature of $37.7^\circ\text{C}$ ( $99.9^\circ\text{F}$ ), blood pressure of $118/74\text{ mm Hg}$ , pulse of $108/\text{min}$ , and respiratory rate of $26/\text{min}$ . Pulse oximetry reveals an oxygen saturation of $85\%$ on room air.

Physical examination demonstrates a somnolent patient who awakens easily to verbal stimuli and follows simple commands. The anteroposterior chest diameter is increased. Auscultation reveals a prolonged expiratory phase with diffuse wheezing bilaterally, as well as coarse crackles localized to the right lower lung field. Cardiac examination shows a regular tachycardia with distant heart sounds and no murmurs. Trace bilateral ankle edema is present.

Laboratory results are as follows:

Laboratory Test	Result	Reference Range
Leukocyte count	$14,500/\text{mm}^3$	$4,500\text{--}11,000/\text{mm}^3$
Serum sodium	$136\text{ mEq/L}$	$136\text{--}145\text{ mEq/L}$
Serum potassium	$4.1\text{ mEq/L}$	$3.5\text{--}5.0\text{ mEq/L}$
Serum chloride	$94\text{ mEq/L}$	$98\text{--}106\text{ mEq/L}$
Serum bicarbonate	$35\text{ mEq/L}$	$22\text{--}28\text{ mEq/L}$
Blood urea nitrogen	$28\text{ mg/dL}$	$8\text{--}20\text{ mg/dL}$
Serum creatinine	$1.1\text{ mg/dL}$	$0.7\text{--}1.3\text{ mg/dL}$
Thyroid-stimulating hormone (TSH)	$0.2\text{ }\mu\text{U/mL}$	$0.4\text{--}4.0\text{ }\mu\text{U/mL}$
Free thyroxine (T4)	$0.7\text{ ng/dL}$	$0.9\text{--}1.7\text{ ng/dL}$

An arterial blood gas analysis obtained on room air demonstrates:

Parameter	Result
$\text{pH}$	$7.25$
$\text{PaO}_2$	$52\text{ mm Hg}$
$\text{PaCO}_2$	$78\text{ mm Hg}$

A portable chest radiograph displays hyperinflated lung fields, flattened hemidiaphragms, and a dense alveolar opacity in the right lower lobe. The cardiac silhouette is normal in size.

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

Initiate noninvasive positive-pressure ventilation and administer intravenous ceftriaxone and azithromycinAnswer
B
Administer intravenous furosemide and initiate a continuous nitroglycerin infusion
C
Administer an intravenous bolus of sodium bicarbonate to rapidly correct the acidemia
D
Initiate intravenous vancomycin and meropenem to provide broad-spectrum antimicrobial coverage
E
Administer intravenous levothyroxine and hydrocortisone for suspected endocrine failure

Answer

The most appropriate next step is to initiate noninvasive positive-pressure ventilation (NPPV) and administer standard-spectrum antibiotics for community-acquired pneumonia (e.g., ceftriaxone and azithromycin).

This patient is experiencing an acute exacerbation of chronic obstructive pulmonary disease (COPD) complicated by acute-on-chronic hypercapnic respiratory failure, as evidenced by his pH of 7.25 and PaCO2 of 78 mm Hg. In patients with a COPD exacerbation and respiratory acidosis (pH < 7.30), a trial of noninvasive positive-pressure ventilation (NPPV) is the standard of care, provided the patient is not entirely comatose and can protect their airway (this patient awakens easily to verbal stimuli). Furthermore, the clinical picture of fever, purulent sputum, leukocytosis, and a right lower lobe consolidation indicates that community-acquired pneumonia (CAP) is the trigger. Standard inpatient treatment for CAP without risk factors for multidrug-resistant organisms includes a beta-lactam and a macrolide (e.g., ceftriaxone and azithromycin).

Step-by-Step Solution

Analyze the arterial blood gas (ABG) and clinical presentation.

The ABG shows a pH of 7.25, PaCO2 of 78 mm Hg, and HCO3 of 35 mEq/L, indicating acute-on-chronic respiratory acidosis. The patient is somnolent but can protect his airway.

Identifying hypercapnic respiratory failure with a pH < 7.30 establishes the immediate need for ventilatory support, with NPPV being the first-line choice for conscious patients.

Identify the underlying trigger for the respiratory decompensation.

Fever, leukocytosis, and a right lower lobe opacity on the chest radiograph indicate community-acquired pneumonia (CAP) as the trigger for the COPD exacerbation.

Treating the underlying trigger is essential for resolving the exacerbation.

Select the appropriate pharmacologic and supportive therapies.

Standard CAP coverage (e.g., a beta-lactam plus a macrolide) is chosen. Broad-spectrum agents, diuretics, or thyroid hormones are excluded.

There are no risk factors for multidrug-resistant organisms, no evidence of acute heart failure, and the thyroid labs reflect euthyroid sick syndrome, which requires no treatment.

Key Concept

Management of acute-on-chronic respiratory acidosis in COPD exacerbations requires NPPV (if the patient can protect their airway) alongside targeted treatment of the underlying trigger (e.g., standard-spectrum antibiotics for community-acquired pneumonia).

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