Most Appropriate Initial Management: Broad-Spectrum Antibiotics
The correct answer is B - Broad spectrum antibiotics. This post-operative knee replacement patient presenting with fever (38°C), leukocytosis (WBC 15), and right lower lobe infiltrate on chest X-ray meets diagnostic criteria for hospital-acquired pneumonia (HAP), which requires immediate empiric broad-spectrum antibiotic therapy before any other intervention 1, 2.
Clinical Reasoning
Why Antibiotics Are the Priority
HAP diagnostic criteria are met: The presence of fever >38°C, leukocytosis, and a new radiographic infiltrate represents the most accurate clinical criteria for initiating empiric antibiotic therapy in the postoperative setting 1.
Pneumonia is the immediate life-threatening concern: Lower respiratory tract infections remain the most deadly communicable disease, and hospital-acquired pneumonia in post-surgical patients carries significant morbidity and mortality risk 2.
Dual infection risk exists: While periprosthetic joint infection (PJI) must be considered in any post-knee replacement patient with fever, the radiographic pneumonia is the more urgent threat requiring immediate treatment 1, 3.
Critical Actions Before Antibiotic Administration
Obtain blood cultures immediately before starting antibiotics to identify causative organisms 1.
Consider sputum cultures if the patient has a productive cough 1.
Do NOT delay antibiotics for joint aspiration in this scenario - the pneumonia takes precedence, though you should still obtain inflammatory markers (ESR, CRP, IL-6) simultaneously to evaluate for occult PJI 1, 3, 4.
Why Other Options Are Incorrect
IV fluids (Option A) are supportive care but do not address the underlying infection driving the fever and leukocytosis. Pneumonia requires antimicrobial therapy, not just hydration 1.
Antipyretics (Option C) only mask symptoms without treating the life-threatening infection. This would be dangerous temporizing that delays definitive management 1.
DVT prophylaxis (Option D) should already be in place post-operatively, but is not the acute intervention needed for active infection 1.
Important Caveats About This Case
The Peripheral WBC Count Is Misleading
WBC 15 does not exclude PJI: Peripheral leukocyte counts are not elevated in most patients with infected prostheses, making this finding meaningless for ruling out joint infection 5, 3, 4.
CRP is far more reliable: C-reactive protein has 73-91% sensitivity and 81-86% specificity for prosthetic knee infection (cutoff ≥13.5 mg/L), compared to WBC which is essentially useless for PJI diagnosis 1, 3, 4.
Dual Pathology Must Be Considered
Obtain inflammatory markers now: ESR, CRP, and serum interleukin-6 should be drawn immediately to evaluate for occult PJI, as recommended by the American Academy of Orthopaedic Surgeons 1, 3, 4.
Plan for joint aspiration: Once the pneumonia is stabilized (typically by Day 3), perform knee joint aspiration for synovial fluid analysis if inflammatory markers are elevated or clinical suspicion for PJI remains 1, 4.
Antibiotic timing dilemma: Ideally, antibiotics should be withheld for at least 2 weeks before joint aspiration to avoid false-negative cultures, but this is not feasible when treating active pneumonia - balance the need to treat HAP against the risk of masking PJI 1, 4.
Antibiotic Selection
Broad-spectrum coverage is essential for HAP in the post-surgical setting, typically covering Staphylococcus aureus, Streptococcus pneumoniae, Haemophilus influenzae, Klebsiella pneumoniae, and other common respiratory pathogens 6, 2.
Ceftriaxone is FDA-approved for lower respiratory tract infections caused by these organisms and provides excellent coverage for hospital-acquired pneumonia 6.
Reassess by Day 3 based on culture results and clinical response, narrowing the antibiotic spectrum as appropriate 1.