eMedicine Specialties > Pulmonology > Infectious Lung Diseases

Ventilator-Associated Pneumonia

Author: Shakeel Amanullah, MD, Consulting Staff, Pulmonary, Critical Care, and Sleep Medicine, Clarian Arnett Health
Coauthor(s): David H Posner, MD, Assistant Professor of Medicine, New York University School of Medicine; Assistant Chief of Pulmonary Diseases, Instructor, Intensive Care Unit, Education Coordinator for Pulmonary Fellowship, Lenox Hill Hospital
Contributor Information and Disclosures

Updated: Jun 29, 2009

Introduction

Background

An understanding of the following terminology used to describe nosocomial pneumonias is important.

• Hospital-acquired pneumonia (HAP) is pneumonia that develops 48 hours or longer after admission to a hospital.
• Ventilator-associated pneumonia (VAP) is pneumonia that develops 48 hours or longer after mechanical ventilation is given by means of an endotracheal tube or tracheostomy.
• Health care–associated pneumonia is pneumonia that occurs in persons in one of the following groups:
  • Patients who have been hospitalized in an acute care facility for 2 or more days within 90 days of the infection
  • Residents of a nursing home or long-term care facility
  • Patients who received intravenous antibiotic therapy, chemotherapy, or wound care within the last 30 days of the current infection
  • Patients who receive hemodialysis in any setting

HAP is the second most common nosocomial infection (see Nosocomial Pneumonia). HAP increases a patient's hospital stay by approximately 7-9 days and can increase hospital costs by an average of $40,000 per patient.^1,2,3

The eMedicine article Pneumonia, Community-Acquired may be of interest.

Pathophysiology

VAP results from the invasion of the lower respiratory tract and lung parenchyma by microorganisms. Intubation compromises the integrity of the oropharynx and trachea and allows oral and gastric secretions to enter the lower airways.

Frequency

International

VAP is a complication in as many as 28% of patients who receive mechanical ventilation. The incidence of VAP increases with the duration of mechanical ventilation. Estimated rates are 3% per day for the first 5 days, 2% per day for days 6-10, and 1% per day after day 10.⁴

Mortality/Morbidity

The crude mortality rate for VAP is 27-76%. Pseudomonas or Acinetobacter pneumonia is associated with increased mortality rates compared with other organisms. Studies have consistently shown that a delay in starting appropriate and adequately dosed antibiotic therapy increases the mortality risk.

Outcomes are also related to the timing of the onset of VAP. Early-onset pneumonia occurs within the first 4 days of hospitalization, whereas late-onset VAP develops 5 or more days after admission. Late-onset pneumonias are usually associated with multidrug-resistant (MDR) organisms.

Race

No specific data are available.

Sex

No specific data are available.

Age

No specific data are available.

Clinical

History

Risk factors for MDR pathogens

The patient's medical history should include an assessment for risk factors related to MDR pathogens. Such risk factors include the following:

• Current hospitalization admission of greater than 5 days
• Hospital admission more than 2 days in the preceding 90 days
• Antibiotic use in the previous 90 days
• Residence in a nursing home or extended-care facility
• Home infusion therapy and wound care
• Long-term dialysis within 30 days
• Immunocompromise

This assessment is important so that appropriate empiric antibiotics can be initiated before bacterial culture results return. If appropriate empiric antibiotics are selected, the subsequent adjustment of antibiotics does not improve the patient's mortality risk.

Diagnostic triad for VAP

The diagnostic triad for VAP consists of the following clinical criteria:

• Pulmonary infection: Signs include fever, purulent secretions, and leucocytosis.
• Bacteriologic evidence of pulmonary infection: See Other Tests.
• Radiologic suggestion of pulmonary infection: See Imaging Studies.

Causes

Multiple factors should be considered when addressing the issues of HAP and VAP. These factors include the following (also see History):

• Whether or not to intubate the patient
• The roue of intubation or placement of tubes
• Feeding the patient
• Body positioning
• Prevention of stress-related bleeding
• Prevention of deep venous thrombosis
• Use of antibiotics and control of colonization

Mechanical ventilation

Intubation with mechanical ventilation increases the risk of HAP 3- to 21-fold^6,7,8,5 and should be avoided if possible. Noninvasive positive-pressure ventilation is an option to consider, especially in the following groups:

• Patients with exacerbations of chronic obstructive pulmonary disease
• Patients with acute hypoxic respiratory failure
• Patients with immunosuppression and respiratory failure

Orotracheal and orogastric tubes are preferred over nasal devices to reduce the risk of VAP, although direct causality has not been proven.

Continuous aspiration of subglottic secretions reduces the risk of early-onset VAP. Cuff pressures should be maintained at greater than 20 cm of water to prevent aspiration around the endotracheal tube.

Passive humidifiers or heat moisture exchangers are preferred to reduce colonization of the ventilator circuit. Ventilatory-circuit condensation should be prevented from entering the endotracheal tubes and any inline nebulizer. Frequent changes of the ventilator circuit, however, have not been shown to reduce the risk of VAP and are currently not recommended.

Protocols for sedation and weaning should be applied in the ICU to reduce the duration of mechanical ventilation.

Feeding, aspiration, and body positioning

Placing patients in a semirecumbent position is associated with approximately a 3-fold reduction in the risk of HAP,⁹ especially during enteral feeding.

Early enteral feeding is currently recommended. Although this route of feeding is associated with an increased incidence of HAP, it offers a number of advantages in delivering nutrition. Investigators have compared the risks of ICU-acquired HAP between gastric and postpyloric feeding. Individual studies have shown no significant differences. A meta-analysis of these studies has suggested a significant reduction in ICU-acquired HAP.¹⁰

Prevention of stress-related bleeding

Studies comparing H2 receptor blockers with sucralfate have shown conflicting results, with a trend toward a reduction of VAP with the use of sucralfate.^11,12,13 These benefits were most notable with late-onset VAP. Use of sucralfate is associated with a 4% increase in clinically significant bleeding. Proton pump inhibitors also may be used to prevent stress-related gastrointestinal bleeding.

Prevention of deep venous thrombosis

Measures should be taken to prevent deep venous thrombosis. The selection for the method of deep venous thrombosis prevention should be based on individual patient characteristics and comorbid illnesses. Heparin, low molecular weight heparin, and compression stockings are means to help prevent deep venous thrombosis.

Use of antibiotics and control of colonization

Rinses with oral chlorhexidine help prevent ICU-acquired HAP in patients undergoing coronory artery bypass procedures.¹⁴ However, in a randomized controlled trial in 417 ICU patients, Panchabhai et al found that twice-daily oropharyngeal cleansing with 0.2% chlorhexidine solution had no prophylactic benefit for nosocomial pneumonia. Pneumonia developed in 7.1% of patients receiving chlorhexidine cleansing, compared with 7.7% of those in the control group, who received 0.01% potassium permanganate solution. Among patients who developed pneumonia, no significant difference was noted between the study group and the control group in the median day of development of pneumonia, median ICU stay, or mortality.¹⁵

A history of antibiotic use prior to the onset of VAP increases the probability of infection with MDR pathogens.

Alteration of the florae in the digestive tract due to oral or systemic antibiotics (ie, selective decontamination of the digestive tract) effectively reduces the incidence of ICU-acquired HAP in ICUs where the levels of antibiotic resistance are low. However, routine use of this approach is not recommended.

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