Ventilator-Associated Pneumonia and Hospital-Acquired Pneumonia

Microbiology

See below for MRSA/PsA information. In addition, Atypical bacteria (e.g. Mycoplasma, Chlamydiae, Legionella) don't generally cause VAP.  Consequently, atypical coverage is generally not utilized. Anaerobic coverage for pulmonary infections is generally indicated only in the context of empyema or lung abscess.

Diagnosis

Clinical Picture

• worsening oxygenation and compliance
• chest infiltrates (CXR, CT, POCUS)
• Neutrophilia and left shift, fever, sputum production

Definitions

• There is no gold standard for the diagnosis of HAP or VAP.
• HAP is defined as a pneumonia not incubating at the time of hospital admission and occurring 48 hours or more after admission.
• VAP is defined as a pneumonia occurring >48 hours after endotracheal intubation.

Investigations

• sampling methods
  • noninvasive sampling with semiquantitative cultures (endotracheal aspiration) are preferred over invasive sampling (bronchoscopic techniques)
    • This is because bronchoscopy hasn't been shown to affect mortality or length of stay in VAP
    • Bronchoscopy probably warranted to exclude PJP/invasive pulmonary Aspergillosis if these are seriously on the differential (leukopenia, steroids, HIV, other immunosuppression)
    • Cutoffs for diagnostic threshold for VAP if invasive methods are used:
      • Protected specimen brush (PSB) - 10^3 CFU/mL
      • BAL - 10^4 CFU/mL
  • nares swab for MRSA
• biomarkers
  • CRP, PCT, etc are not routinely recommended in the decision to start antibiotic therapy
• blood cultures
  • approximately 15% of patients with VAP are bacteremic
  • at least 25% of positive blood cultures in suspected VAP patients are from a nonpulmonary source
• Repeat imaging

Differential

Always thinking about these! Viral pneumonia, ARDS, atelectasis, pulmonary edema, aspiration pneumonitis, pulmonary embolism with infarction, interstitial lung disease (e.g. COP, AIP).

Antimicrobial Therapy

Hospital-Acquired Pneumonia

• Suspected HAP - treat according to microbiology (taking into account local AMR) rather than empirically.
  • recommend empiric coverage for Staph aureus - MSSA vs MRSA depends on risk factors (Se below)
    • MSSA + broad spectrum coverage: pip-tazo, cefepime, levofloxacin, meropenem
    • MRSA coverage: vancomycin or linezolid
  • recommend empiric GNB/PsA coverage
    • double vs single depends on risk factors (See below for VAP)

Ventilator-Associated Tracheobronchitis

• Antibiotics are NOT recommended (Weak recommendation, low quality evidence)

Ventilator-Associated Pneumonia

• empiric treatment is guided by local antibiogram and local known pathogens
• in suspected VAP, recommend covering for Staph aureus, Pseudomonas, and other GNB in all empiric regimens
  • MRSA coverage if: risk factors for AMR, >10-20% MRSA prevalence, and unknown MRSA prevalance. Use vancomycin or linezolid. Otherwise MSSA coverage.
    • Empiric MSSA + broad spectrum coverage: pip-tazo, cefepime, levofloxacin, meropenem.
    • a negative nares MRSA PCR essentially means the risk of MRSA VAP is <2% -- consider this a test of exclusion (NOT in guideline)
  • Double Pseudomonal coverage recommended for: risk factors for AMR, >10% resistance to the monotherapy, and unknown resistance prevalence (weak recommendation, low quality) Single Pseudomonal coverage otherwise.
  • Avoid aminoglycosides, colistin if possible

Inhaled antibiotic therapy

• If the patient has VAP due to GNB susceptible to only aminoglycosides or polymyxins (colistin, polymyxin B) then recommended to treat with BOTH inhaled and systemic antibiotics
• It is reasonable to consider adjunctive inhaled antibiotic therapy as a treatment of last resort for patients who are not responding to intravenous antibiotics alone, whether the infecting organism is or is not multidrug resistant (MDR).

Proven MRSA HAP/VAP

Treat with vancomycin or linezolid.

Proven Pseudomonas HAP/VAP

• Definitive treatment should be guided by resistance testing.
• Aminoglycoside monotherapy is not recommended in any setting.
• If the patient is stable, and the resistance profile is known, then treat with monotherapy with a susceptible agent.
• If the patient is NOT stable (septic shock, high risk of death which is >25%) even if the resistance profile is known, then consider combination therapy (2 antibiotics). Once the septic shock resolves, then step down to monotherapy.

Proven ESBL HAP/VAP

• Definite treatment should be based on resistance profiles.

Proven Acinetobacter HAP/VAP

• Reminder: this is a SPICE-HAM (AmpC) bug
• Treat with a carbapenem or amp/sulbactam if susceptible.
• If only sensitive to polymyxins then treat with IV polymyxin (colistin, polymyxin B) + adjunct inhaled colistin (see above)
• Tigecycline is recommended against
• Adjunct rifampicin is not recommended in addition to colistin.

Proven Carbapenem-resistant pathogens

• Generally treated with IV polymyxin + inhaled colistin

Duration of Therapy

• VAP: 7 days (as opposed to 8-15 days)
• HAP: 7 days

De-escalation and Discontinuation

• De-escalate antibiotics when appropriate (combination therapy --> monotherapy, broad spectrum --> targeted)
• PCT levels + clinical criteria to guide discontinuation (PCT not available widely in Canada)

References

1. 2016 IDSA/ATS HAP/VAP Guidelines
2. Ventilator Associated Pneumonia (VAP) - EMCrit Project