What are the management criteria for high-risk community-acquired pneumonia (CAP)?

High-Risk Community-Acquired Pneumonia: Criteria and Management

High-risk CAP requiring ICU admission is defined by the presence of either one major criterion (mechanical ventilation or septic shock) OR two of three minor criteria (systolic BP <90 mmHg, multilobar disease, or PaO2/FiO2 ratio <250), and should be treated with a β-lactam plus either a macrolide or respiratory fluoroquinolone. 1

ICU Admission Criteria

Major Criteria (One Required for ICU Admission)

• Need for mechanical ventilation 1
• Septic shock or need for vasopressors 1

Minor Criteria (Two of Three Required for ICU Admission)

• Systolic blood pressure ≤90 mmHg 1
• Multilobar disease or bilateral pneumonia 1
• PaO2/FiO2 ratio ≤250 1

This rule achieves 78% sensitivity, 94% specificity, 75% positive predictive value, and 95% negative predictive value for predicting ICU admission need. 1

Additional High-Risk Indicators

While not formally validated for ICU admission criteria, the following suggest severe illness and should prompt consideration for higher-level care:

• Respiratory rate ≥30/min 1
• Diastolic blood pressure <60 mmHg 1
• Confusion or altered mental status 1
• Blood urea nitrogen ≥19.6 mg/dL (≥7.0 mM) 1
• Severe respiratory failure (PaO2/FiO2 <250) 1
• Radiographic extension of infiltrates by ≥50% within 48 hours 1
• Acute renal failure (urine output ≤80 mL in 4 hours or creatinine ≥2 mg/dL) 1

Empiric Antibiotic Management for Severe CAP

Standard Severe CAP (No Pseudomonas Risk Factors)

First-line regimen: β-lactam (ceftriaxone, cefotaxime, or ampicillin-sulbactam) PLUS either azithromycin OR a respiratory fluoroquinolone (levofloxacin or moxifloxacin). 1, 2

Critical caveat: Fluoroquinolone monotherapy is NOT supported for ICU patients and should be avoided. 1

Severe CAP with Pseudomonas Risk Factors

Antipseudomonal regimen required: Antipseudomonal β-lactam (piperacillin-tazobactam, cefepime, imipenem, or meropenem) PLUS ciprofloxacin or levofloxacin (750 mg). 1, 2

Pseudomonas risk factors include:

• Bronchiectasis 1
• Broad-spectrum antibiotic therapy for ≥7 days in the past month 1
• Malnutrition 1
• Chronic corticosteroid therapy (≥10 mg/day) 1

Important: Reserve antipseudomonal agents (cefepime, carbapenems, piperacillin-tazobactam) exclusively for patients with documented risk factors to prevent unnecessary broad-spectrum coverage. 1

Diagnostic Workup for Severe CAP

Mandatory Testing

• Two sets of blood cultures before antibiotics 1
• Arterial blood gas or pulse oximetry 1
• Routine blood chemistry and complete blood count 1
• Chest radiograph 1
• Legionella urinary antigen 1

Additional Diagnostic Considerations

• Sputum culture with Gram stain if drug-resistant or unusual pathogen suspected 1
• Bronchoscopic sampling (protected specimen brush or bronchoalveolar lavage) in selected severe cases, particularly for intubated patients 1
• Diagnostic thoracentesis when significant pleural effusion present 1
• COVID-19 and influenza testing when these viruses are circulating in the community 3

Avoid routine serologic testing as it does not guide initial management. 1

Timing and Administration

Critical Time Benchmarks

• First antibiotic dose within 8 hours of hospital arrival for all admitted patients 1
• First dose while still in the emergency department for patients admitted through the ED 1, 2

Delayed antibiotic administration in severe CAP is associated with worse outcomes, particularly for Streptococcus pneumoniae and Legionella pneumophila. 4

Pathogen Coverage Rationale

Primary Pathogens in Severe CAP

• Streptococcus pneumoniae (most common, including drug-resistant strains) 1, 3
• Legionella species (especially in ICU patients) 1
• Atypical pathogens (Chlamydia pneumoniae, Mycoplasma pneumoniae) 1
• Enteric gram-negative organisms 1
• Pseudomonas aeruginosa (only with specific risk factors) 1

All severe CAP patients require atypical pathogen coverage because these organisms can occur alone or as mixed infections, and delayed coverage of Legionella increases mortality. 1, 4

Adjunctive Therapies for Severe CAP

Corticosteroids

Systemic corticosteroids within 24 hours of severe CAP development may reduce 28-day mortality. 3

Hemodynamic Support

• Screen for occult adrenal insufficiency in hypotensive, fluid-resuscitated patients 1
• Consider drotrecogin alfa activated within 24 hours for persistent septic shock despite adequate fluid resuscitation 1

Respiratory Support

• Cautious trial of noninvasive ventilation for hypoxemia or respiratory distress, unless severe hypoxemia (PaO2/FiO2 <150) with bilateral infiltrates requires immediate intubation 1
• Low-tidal-volume ventilation (6 mL/kg ideal body weight) for mechanically ventilated patients with diffuse bilateral pneumonia or ARDS 1

Duration of Therapy

• Minimum 5 days of treatment for all CAP patients 1, 5, 2
• Extend to 7 days for suspected or proven MRSA or Pseudomonas aeruginosa 5, 2
• Extend to 14-21 days for Legionella, staphylococcal, or gram-negative enteric bacilli when confirmed 2

Patients must be afebrile for 48-72 hours and have no more than one CAP-associated sign of clinical instability before discontinuation. 1

Switching to Oral Therapy

Switch from IV to oral when:

• Hemodynamically stable 1, 2
• Clinically improving 1, 2
• Able to ingest medications 1, 2
• Functioning gastrointestinal tract 1, 2
• Afebrile (<100°F) on two occasions 8 hours apart 1
• Decreasing white blood cell count 1, 5

Patients can be discharged the same day as oral switch if other medical and social factors permit. 1

Management of Treatment Failure

Up to 15% of CAP patients fail to respond to initial therapy. 1

Systematic Approach to Non-Response

Do not change antibiotics in the first 72 hours unless marked clinical deterioration occurs. 1

After 72 hours without improvement, evaluate for:

• Drug-resistant or unusual pathogens 1, 2
• Non-pneumonia diagnosis (inflammatory disease, pulmonary embolus) 1, 2
• Pneumonia complications (empyema, lung abscess) 1, 2

Obtain CT scan to reveal unsuspected pleural fluid collections, lung nodules, or cavitation. 2

Common Pitfalls to Avoid

• Never use fluoroquinolone monotherapy in ICU patients despite its efficacy in non-severe CAP 1
• Do not rely on sputum Gram stain alone to narrow initial empiric therapy, though it can broaden coverage if organisms not covered by usual regimens are identified 1
• Avoid delaying antibiotics beyond 8 hours while awaiting diagnostic test results 1
• Do not treat for less than 5 days even if clinical stability achieved earlier 1, 5, 2
• Abandon the healthcare-associated pneumonia (HCAP) classification—only cover MRSA or Pseudomonas if locally validated risk factors present 5, 2