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A subset of HAP, Ventilator-Associated Pneumonia (VAP) refers to those cases that occur in patients who have been on ventilator support for at least 48 hours. The mechanisms for HAP and VAP infections are similar, although due to the fact that host defenses against pneumonia are so effectively bypassed by an endotracheal tube, the risk of pneumonia in ventilated patients is much higher.

Early-onset VAP is defined as hospital-acquired pneumonia that develops in patients who have been on a ventilator between 48 and 96 hours or less than four days. These patients may have had emergent, traumatic intubations or major chest, abdominal or neurosurgery. The usual pathogens associated with early onset VAP are most commonly the patient’s own normal, antibiotic-sensitive flora, such as methicillinsensitive Staphylococcus aureus (MSSA), Haemophilus influenza or Streptococcus pneumoniae.

Late-onset VAP is defined as hospital-acquired pneumonia that develops in patients who have been on a ventilator five days or longer. These patients often present with many pre-existing chronic conditions that predispose them to lung infections, such as chronic obstructive pulmonary disease (COPD) or cardiac-related pulmonary edema. The pathogens most commonly seen with late-onset VAP are the more resistant strains of bacteria such as methicillin-resistant Staphylococcus aureus (MRSA) or gram-negative bacteria such as Pseudomonas aeruginosa, Acinetobacter, Enterobacter, Klebsiella or Serratia.

Ventilated patients are especially susceptible to pneumonia as their normal host defenses are hampered, blocked or disabled during mechanical ventilation by the physical presence of the assisted-breathing device. The bacteria and other microorganisms, which are normally blocked or carried away from the respiratory tract, have the ability to bypass the normal body defenses and enter the lungs. In order to understand the vulnerabilities of the ventilated patient, a review of the normal reflexes and clearance mechanisms is helpful.

Handwashing
The practice of handwashing and the wearing of gowns and gloves are basic and quite possibly the most important actions taken for reducing colonization. Methicillin Resistant Staphylococcus aureus (MRSA) is commonly spread by caregivers’ hands.12 Gloves and gowns have been shown to be effective in preventing the nosocomial spread of antibiotic resistant bacteria including Vancomycin-resistant enterococci (VRE) as well as MRSA.

Oral Hygiene
The importance of patient oral and nasal hygiene is often overlooked, although it is one of the most basic of nursing interventions. Sole found that less than half of the 27 surveyed sites (48%) had written policies for oral care of intubated patients, and even fewer (37%) had oral suction policies.22 The use of closed suction systems (CSS) may contribute to the inattention paid to oral care in that oral suctioning is an integral part of traditional open suction procedures. Yet, it is widely recognized that the mouth is a virtual garden of normal bacterial flora and pathogenic organisms. Both Kollef7 and Kunis12 have advocated chlorhexidine oral rinse to reduce the oral bacterial load; however, its regular use may lead to chlorhexidine resistant organisms. Several studies have shown that oral decontamination is an effective method for reducing VAP.

• preventing cough (the patients natural defense)
• preventing upper airway filtering
  
• preventing upper airway humidification
  
• inhibiting epiglottic and upper airway reflexes
  
• inhibiting cilliary transport by the epithelium
  
• acting as a direct conduit into the lungs for airborne pathogens
  
• potentially acting as a reservoir for pathogens by providing a place for biofilm to form
  
• having a cuff which provides a place for secretions to “pool” in the hypoglottic area
  
• initiating a foreign body reaction, interfering with the local immune response

Host or patient risk factors include:

• age of 65 or more
  
• underlying chronic illness (e.g. Chronic Obstructive Pulmonary Disease (COPD), emphysema, asthma)
  
• immunosuppression
  
• depressed consciousness
  
• thoracic or abdominal surgery
  
• previous antibiotic therapy
  
• previous pneumonia or remote infection

Other device treatment and personnel related risk factors include:

• nasogastric tube placement
  
• bolus enteral feeding
  
• gastric over-distension
  
• stress ulcer treatment
  
• supine patient position
  
• nasal intubation route
  
• instillation of normal saline
  
• understaffing
  
• nonconformance to handwashing protocol
  
• indiscriminate use of antibiotics
  
• lack of training in VAP prevention