Ventilator-Associated Pneumonia

Ventilator-Associated Pneumonia (VAP)

Definitions

• Ventilator-Associated Pneumonia (VAP): Pneumonia that develops 48 hours or more after a patient has been placed on mechanical ventilation.
• Hospital-Acquired Pneumonia (HAP): Pneumonia that occurs 48 hours or longer after admission to the hospital, resulting from an infection not incubating at the time of admission.
• Health Care–Associated Pneumonia (HCAP): Pneumonia that affects patients residing in long-term or acute care facilities.

Onset

• Early Onset VAP: Occurs 48 to 72 hours after tracheal intubation.
• Typically caused by antibiotic-sensitive bacteria.
• Late Onset VAP: Occurs later than 72 hours after intubation.
• More likely to be caused by multidrug-resistant (MDR) pathogens.

Epidemiology

• VAP is the most common nosocomial infection in the intensive care unit (ICU).
• Risk:
  • 3% per day during the first 5 days on mechanical ventilation.
  • 2% per day during days 5 to 10.
  • 1% per day thereafter.
• Incidence: 8% to 28% for all intubated patients.
• Mortality: 5% to 48%, varying based on infecting organism, underlying disease, and prior antimicrobial therapy.

Common Organisms

• Gram-Negative Aerobes:
  • Pseudomonas aeruginosa
  • Klebsiella pneumoniae
  • Escherichia coli
  • Enterobacter spp.
  • Serratia marcescens
  • Acinetobacter calcoaceticus
  • Proteus mirabilis
  • Haemophilus influenzae
• Gram-Positive Aerobes:
  • Staphylococcus aureus
  • Streptococcus pneumoniae
• Gram-Negative Anaerobes:
  • Bacteroides fragilis
• Fungi:
  • Candida albicans
• Others:
  • Legionella pneumophila
  • Severe acute respiratory syndrome (SARS) virus
  • Influenza A virus

Conditions and Risk Factors

• Alcoholism
• Antibiotic therapy
• Diabetes mellitus
• Hypoxemia
• Bronchoscopy
• Intubation
• Tracheostomy
• Chest tube thoracostomy
• Hypotension
• Nasogastric tubes/enteral feedings
• Acidosis
• Malnutrition
• Azotemia
• Preceding viral infection
• Leukocytopenia
• Surgery
• Leukocytosis
• Underlying illness
• Underlying pulmonary disease
• Nasal intubation
• Gastric alkalinization
• Supine position
• Immunosuppression
• Radiation/scarring
• Malignancy
• Coma
• Circuit/airway manipulation (<72-hour circuit changes)
• Severe illness (Acute Physiology and Chronic Health Evaluation [APACHE] score ≥18)

Pharmacologic

• Concurrent steroid therapy
• Inappropriate antimicrobial therapy
• Overuse of sedatives and paralytics
• Use of type 2 (H2) histamine antagonists and gastroprotective agents (e.g., antacids)
• Multidrug-resistant organisms (MDRs)

Nonpharmacologic

• Need for endotracheal tube (ET) or tracheostomy tube during ventilation
• Routine care of ventilator circuits, humidifiers, nebulizers
• Use of respirometers, reusable electronic ventilator probes and sensors, bronchoscopes, endoscopes

Pathogenesis of VAP

• The upper airways of healthy individuals typically contain nonpathogenic bacteria such as the viridans group of streptococci, Haemophilus spp., and anaerobes.
• P. aeruginosa and Acinetobacter are rarely found in healthy respiratory tracts due to anatomic barriers.
• The pathogenesis of VAP most often involves:
  • Colonization of the aerodigestive tract with pathogenic bacteria.
  • Aspiration of contaminated secretions into the lower airways.
  • Colonization of the lower airways and lung parenchyma with infectious microorganisms.
• During critical illnesses and mechanical ventilation, the oropharyngeal flora shifts to gram-negative bacilli and S. aureus.
• Aspiration occurs because the patient is unable to protect the lower airways.

Diagnosis of VAP

• Lack of a precise definition for the diagnosis of VAP.
• Relying solely on clinical findings can be subjective and lead to inaccurate diagnosis.
• Inaccurate diagnosis can lead to inappropriate antibiotic therapy, especially if the infection is polymicrobial or involves drug-resistant organisms.
• In 2011, the CDC and NHSN proposed an updated definition incorporating the general features of the ATS/IDSA definition.

CDC Surveillance Definition

• Uses the term ventilator-associated event (VAE) to describe conditions and complications in mechanically ventilated patients, including VAP.
• VAEs are categorized as:
  • Ventilator-associated condition (VAC)
  • Infection-related ventilator-associated complication (IVAC)
  • Possible pneumonia or probable pneumonia
• Diagnosis relies on:
  • Objective data
  • Clearly defined time criteria
  • Exclusion of radiographic imaging

CDC Surveillance Paradigm for VAE

• Ventilator-Associated Condition (VAC):
  • New respiratory deterioration: ≥2 calendar days of stable or decreasing daily minimum positive end-expiratory pressure (PEEP) or daily minimum fraction of inspired O2, followed by a rise in daily minimum PEEP of ≥3 cm of water or a rise in the daily minimum percentage of inspired O2 by ≥20 points sustained for ≥2 calendar days.
• Infection-Related Ventilator-Associated Complication (IVAC):
  • VAC plus a temperature of
• Possible Pneumonia:
  • IVAC plus Gram staining of endotracheal aspirate or BAL showing ≥25 neutrophils and ≤10 epithelial cells per low-power field or a positive culture for a potentially pathogenic organism, within 2 calendar days before or after onset of a VAC, excluding the first 2 days of mechanical ventilation.
• Probable Pneumonia:
  • IVAC plus Gram staining of endotracheal aspirate or BAL showing ≥25 neutrophils and ≤10 epithelial cells per low-power field, plus endotracheal aspirate with ≥10^5 colony-forming units per milliliter or BAL culture with ≥10^4 colony-forming units per milliliter, or endotracheal aspirate or BAL semiquantitative equivalent, within 2 calendar days before or after onset of a VAC, excluding the first 2 days of mechanical ventilation.

Clinical Criteria (Table 14-1)

Variables:
Temperature, °C
WBC count, /μL
Secretions
PaO2 fraction of Inspired oxygen Chest radiography Microbiology POINTS 0 ≥36.1 to ≤38.4 ≥4,000 to ≤11,000 Absent >240 or ARDS No infiltrate No or light growth 1 point 2, arterial oxygen pressure: WBC, white blood calt

Bacteriologic (Quantitative) Diagnosis

• Obtaining quantitative cultures of specimens from the lower respiratory tract:
  • Fiber-optic bronchoscopy
  • Non-bronchoscopic techniques:
    • Mini bronchoalveolar lavage (BAL)
    • Blinded bronchial sampling (BBS)
    • Blinded sampling with protected-specimen brush (BPSB)
• Bacteriologic studies include:
  • Quantitative culture techniques
  • Microscopic analysis of the cultures using an appropriate stain
  • Direct microscopic and histologic examinations of BAL and PBS samples to identify bacteria

Treatment of VAP

• Initiating empiric antibiotic therapy.
• ATS-IDSA Guidelines provide pathways for clinicians on initiating empiric antibiotic therapy and strategies to reduce the emergence of MDR pathogens.

Strategies to Prevent VAP

• Establish well-designed infection-control practices in the ICU.
• Prioritize VAP prevention.
• Provide adequate physical and human resources for surveillance mechanisms to track the local incidence of VAP and other nosocomial infections.
• Incorporate prevention strategies into ventilator bundles.

Nonpharmacologic Prevention

• Noninvasive ventilation
• Hand washing and adherence to accepted infection control procedures
• Semi-recumbent positioning of the patient
• Appropriate circuit changes when grossly contaminated
• Heat-moisture exchangers when possible
• Aspiration of subglottic secretions
• Appropriate disinfection and sterilization techniques
• Kinetic beds
• Dedicated personnel for monitoring nosocomial VAP rates
• Using closed suction catheters and sterile suction technique
• Avoiding large gastric volumes
• Extubating and removing nasogastric tube as clinically indicated
• Avoiding contamination with ventilator circuit condensate
• Using single-patient items such as monitors, oxygen analyzers, and resuscitation bags
• Carefully using in-line, small-volume nebulizers
• Considering the use of expiratory-line gas traps or filters
• Using oral rather than nasal intubation

Pharmacologic Prevention

• Administering stress ulcer prophylaxis with sucralfate instead of H2 antagonists in patients at high risk for stress ulcers (still controversial).
• Considering possible prophylactic intestinal decontamination (antimicrobial administration).
• Avoiding central nervous system depressants.

Methods to Improve Host Immunity

• Maintain nutritional status
• Avoid agents that impair pulmonary defenses (e.g., aminophylline, anesthetics, certain antibiotics, corticosteroids, sedative narcotics, and antineoplastic agents).
• Minimize the use of invasive procedures when possible.
• Remove or treat disease states that affect host defenses when possible (e.g., acidosis, dehydration, hypoxemia, ethanol intoxication, acid aspiration, stress, thermal injury, diabetic ketoacidosis, liver failure, kidney failure, heart failure).