Ventilator-Associated Pneumonia (VAP)

Ventilator-associated pneumonia (VAP) is a type of hospital-acquired pneumonia that develops in patients who have been on mechanical ventilation through an endotracheal or tracheostomy tube for at least 48 hours. It is a significant cause of morbidity and mortality in the intensive care unit (ICU).

Causes

VAP is primarily caused by bacterial infections, with common pathogens including:

  • Gram-negative bacteria:
    • Pseudomonas aeruginosa
    • Escherichia coli
    • Klebsiella pneumoniae
    • Acinetobacter spp.
  • Gram-positive bacteria:
    • Staphylococcus aureus (including MRSA)
  • Other pathogens:
    • Enterobacteriaceae
    • Legionella pneumophila

Risk Factors

  • Prolonged mechanical ventilation
  • Aspiration of oropharyngeal secretions
  • Use of sedatives and muscle relaxants
  • Prior antibiotic therapy
  • Underlying chronic lung disease
  • Immunosuppression

Signs & Symptoms

  • Fever and chills
  • Increased respiratory secretions, often purulent
  • Worsening gas exchange (hypoxaemia)
  • Increased respiratory rate
  • Increased white blood cell count
  • New or progressive infiltrates on chest X-ray

Pathophysiology

  1. Colonisation and Aspiration:
    • Endotracheal tubes bypass the body’s natural defence mechanisms, allowing direct entry of pathogens.
    • Aspiration of contaminated secretions from the oropharynx or stomach can introduce bacteria into the lower respiratory tract.
  2. Biofilm Formation:
    • Pathogens form biofilms on the surface of the endotracheal tube, which protect them from antibiotics and immune responses.
  3. Inflammatory Response:
    • The presence of bacteria triggers an intense inflammatory response in the lungs.
    • Inflammatory cells and fluid accumulate in the alveoli, leading to impaired gas exchange.

Diagnosis

Diagnosis of VAP involves a combination of clinical, radiographic, and microbiological criteria:

  1. Clinical Criteria:
    • New or progressive infiltrate on chest X-ray
    • At least two of the following: fever, leukocytosis or leukopenia, purulent tracheal secretions.
  2. Microbiological Testing:
    • Tracheal aspirate cultures
    • Bronchoalveolar lavage (BAL) cultures
    • Protected specimen brush (PSB) cultures
  3. Radiographic Imaging:
    • Chest X-ray or CT scan showing new or worsening infiltrates.

Management

  1. Preventive Measures:
    • Ventilator Bundle:
      • Elevating the head of the bed to 30-45 degrees.
      • Daily sedation vacations and assessment of readiness to extubate.
      • Peptic ulcer disease prophylaxis.
      • Deep venous thrombosis prophylaxis.
      • Daily oral care with chlorhexidine.
    • Hand Hygiene: Strict adherence to hand hygiene protocols.
    • Aspiration Precautions: Proper cuff management and subglottic suctioning.
  2. Empirical Antibiotic Therapy:
    • Initiate broad-spectrum antibiotics based on local antibiogram and suspected pathogens.
    • Common choices include:
      • Anti-pseudomonal beta-lactams: Piperacillin-tazobactam, cefepime.
      • Carbapenems: Meropenem, imipenem.
      • MRSA coverage: Vancomycin or linezolid.
    • De-escalate therapy based on culture results and clinical response.
  3. Supportive Care:
    • Continued mechanical ventilation with appropriate settings.
    • Supplemental oxygen to maintain adequate oxygenation.
    • Fluid management to ensure hemodynamic stability.
  4. Monitoring and Follow-Up:
    • Regular assessment of respiratory status, oxygenation, and response to treatment.
    • Adjust antibiotic therapy based on microbiological results and patient progress.

Outcomes

  • Early identification and appropriate management of VAP are crucial to improve outcomes.
  • Prolonged mechanical ventilation and ICU stay are associated with higher morbidity and mortality.
  • Implementation of preventive measures can significantly reduce the incidence of VAP.

References