A 66-year-old man is evaluated in the intensive care unit on day 4 of his admission. He wa… — USMLE Step 2 CK

A 66-year-old man is evaluated in the intensive care unit on day 4 of his admission. He was initially intubated and placed on mechanical ventilation for acute hypercapnic respiratory failure secondary to a severe exacerbation of chronic obstructive pulmonary disease (COPD). Two days ago, he developed a temperature of $38.5^\circ\text{C}$ ( $101.3^\circ\text{F}$ ), increased purulent endotracheal secretions, and a new right lower lobe consolidation on chest radiograph. Empiric therapy with intravenous vancomycin and cefepime was initiated for presumed ventilator-associated pneumonia.

Today, his temperature is $37.2^\circ\text{C}$ ( $99.0^\circ\text{F}$ ), blood pressure is $132/82$ mm Hg, pulse is $84$ /min, and respirations are $16$ /min. He is awake, cooperative, and breathing comfortably on pressure support ventilation. Physical examination shows a prolonged expiratory phase with scattered wheezes and trace bilateral pedal edema.

An arterial blood gas on his current ventilator settings shows:

Parameter	Value	Reference Range
pH	$7.41$	$7.35-7.45$
PaCO $_2$	$54$ mm Hg	$35-45$ mm Hg
PaO $_2$	$76$ mm Hg	$75-105$ mm Hg
HCO $_3^-$	$33$ mEq/L	$22-28$ mEq/L

Endotracheal aspirate cultures obtained two days ago now grow *Streptococcus pneumoniae*. Susceptibility testing shows the organism is sensitive to ceftriaxone, levofloxacin, and penicillin.

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

A
Continue intravenous vancomycin and cefepime for a full 7-day course
De-escalate antibiotic therapy to intravenous ceftriaxoneAnswer
C
Increase the ventilator pressure support to normalize the PaCO $_2$
D
Administer intravenous furosemide
E
Add intravenous azithromycin to the current regimen

Answer

The most appropriate next step is to de-escalate antibiotic therapy to intravenous ceftriaxone.

This patient developed ventilator-associated pneumonia (VAP) and was appropriately started on empiric broad-spectrum antibiotics (vancomycin and cefepime) to cover resistant organisms like MRSA and Pseudomonas aeruginosa. The endotracheal aspirate culture has now returned positive for *Streptococcus pneumoniae* that is sensitive to ceftriaxone. In the setting of clinical improvement (normalizing temperature and stable vital signs), the most appropriate next step is to de-escalate his antimicrobial regimen to a targeted, narrow-spectrum agent like ceftriaxone. Continuing broad-spectrum antibiotics when a susceptible organism is identified is inappropriate and increases the risk of antimicrobial resistance, Clostridioides difficile infection, and drug toxicity.

Step-by-Step Solution

Interpret the clinical response and culture results.

The patient is improving clinically, and cultures show *Streptococcus pneumoniae* sensitive to ceftriaxone.

To determine the need for ongoing broad-spectrum antibiotics.

Apply principles of antibiotic stewardship.

Broad-spectrum agents (vancomycin and cefepime) are discontinued in favor of targeted therapy (ceftriaxone).

To reduce the risk of adverse effects, toxicity, and the development of antimicrobial resistance.

Evaluate the arterial blood gas.

The ABG shows a fully compensated chronic respiratory acidosis with a normal pH (

7.41

) and elevated bicarbonate (

33

mEq/L).

To verify that the patient's current ventilator settings are appropriate and do not require adjustment.

Key Concept

Antibiotic stewardship in ventilator-associated pneumonia (VAP) requires prompt de-escalation from empiric broad-spectrum therapy to targeted narrow-spectrum agents once culture and sensitivity results are available.

Estimated Time:1m 30s

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