A 62-year-old woman is evaluated in the intensive care unit on postoperative day 6 followi… — USMLE Step 2 CK

A 62-year-old woman is evaluated in the intensive care unit on postoperative day 6 following an exploratory laparotomy for a perforated appendix. She remains intubated and mechanically ventilated. Yesterday, she developed a temperature of $38.8^\circ\text{C}$ ( $101.8^\circ\text{F}$ ), increased purulent endotracheal secretions, and an increased oxygen requirement. A chest radiograph showed a new right lower lobe consolidation. Empiric intravenous vancomycin and piperacillin-tazobactam were initiated after obtaining blood and bronchoalveolar lavage (BAL) cultures.

Today, her temperature is $37.5^\circ\text{C}$ ( $99.5^\circ\text{F}$ ). Blood pressure is $118/72$ mm Hg and pulse is $88$ /min.

Arterial blood gas analysis on current ventilator settings:

Variable	Value
pH	$7.30$
$PaCO_2$	$54$ mm Hg
$PaO_2$	$72$ mm Hg
$HCO_3^-$	$26$ mEq/L

The BAL culture from yesterday is now growing $>10^5$ CFU/mL of *Haemophilus influenzae*. Susceptibility testing indicates the organism is sensitive to ceftriaxone, levofloxacin, and piperacillin-tazobactam. Blood cultures show no growth.

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

Discontinue vancomycin and piperacillin-tazobactam and initiate intravenous ceftriaxoneCevap
B
Continue the current regimen of vancomycin and piperacillin-tazobactam
C
Increase the minute ventilation to compensate for a primary metabolic acidosis
D
Administer intravenous furosemide to treat suspected pulmonary edema
E
Perform a lower extremity venous Doppler ultrasound to evaluate for deep vein thrombosis

Cevap

The most appropriate next step is to discontinue vancomycin and piperacillin-tazobactam and initiate intravenous ceftriaxone.

The correct action is to de-escalate the antibiotic regimen. The patient developed ventilator-associated pneumonia (VAP) and was appropriately started on empiric broad-spectrum antibiotics (vancomycin and piperacillin-tazobactam) to cover MRSA and Pseudomonas aeruginosa. However, the bronchoalveolar lavage culture has returned positive only for Haemophilus influenzae, which is sensitive to ceftriaxone. Standard antimicrobial stewardship protocols mandate that once a specific pathogen and its susceptibilities are identified, therapy should be narrowed. Ceftriaxone provides targeted, effective coverage for H. influenzae while minimizing the adverse effects and resistance risks associated with broader agents.

Adım Adım Çözüm

Diagnose the cause of respiratory decompensation based on clinical findings.

The patient has ventilator-associated pneumonia (VAP), evidenced by fever, purulent secretions, new lung consolidation, and positive BAL culture occurring >48 hours after intubation.

Establishing the correct clinical syndrome dictates the appropriate treatment pathway and rules out cardiogenic or thromboembolic etiologies.

Interpret the arterial blood gas (ABG) values.

The low pH (

7.30

) and elevated

PaCO_2

(

54

mm Hg) with near-normal

HCO_3^-

(

26

mEq/L) indicate an acute, uncompensated respiratory acidosis.

Accurate ABG interpretation ensures ventilator management aligns with the primary acid-base disturbance rather than misinterpreting it as a metabolic issue.

Apply principles of antimicrobial stewardship to the culture results.

The BAL confirms a single pathogen (*Haemophilus influenzae*) sensitive to ceftriaxone. Broad-spectrum empiric coverage (vancomycin for MRSA and piperacillin-tazobactam for Pseudomonas) is no longer necessary.

De-escalating to the narrowest-spectrum effective antibiotic minimizes the risk of multi-drug resistant organism emergence, reduces toxicity, and lowers the risk of C. difficile infection.

Anahtar Kavram

Antimicrobial stewardship and antibiotic de-escalation in ventilator-associated pneumonia (VAP)

Soru

Cevap

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