Chapter 4: Ventilator-Associated Pneumonia

Although the term ventilator-associated pneumonia (VAP) implies that the ventilator is the cause of the nosocomial pneumonia, a more appropriate term is artificial airway-associated pneumonia. Although contamination of the ventilator circuit may cause VAP, the most common cause is aspiration of contaminated oral secretions (Figure 4-1). VAP has become an increasing concern because it is not only associated with increased cost, but also with increased time on the ventilator, morbidity, and possibly mortality. It has been estimated that VAP results in an additional cost of about $50,000 per case. Thus third-party payers are evaluating whether the hospital should assume the cost of this iatrogenic infection. Therefore, VAP has become a major concern for hospitals, physicians, respiratory therapists, and nurses caring for ventilated patients. There has been much investigation of risk factors for VAP and effective strategies to decrease VAP rate. In this chapter the definition of VAP, causes of VAP, and strategies to reduce VAP are discussed.

Ventilator Circuit Versus the Artificial Airway

VAP is the result of organisms introduced into the respiratory tract during mechanical ventilation. This can arise from the ventilator circuit or by aspiration of contaminated secretions from above the cuff of the artificial airway. If a clean circuit is used and the patient is never disconnected, the organisms that accumulate in the circuit arise from the patient. However, if the circuit is disconnected and care is not taken to avoid contamination, the circuit could potentially cause VAP. This, however, is less likely to occur than the aspiration of contaminated oropharyngeal secretions.

The primary source of VAP is the aspiration of contaminated oropharyngeal secretions around the airway cuff (Figure 4-2). This occurs because of longitudinal folds that develop in inflated cuffs. To minimize this leakage, it is important to avoid accumulation of secretions above the cuff and to ensure that gastric contents do not move into the pharynx.

Early Versus Late VAP

VAP has frequently been categorized as early or late. Early VAP is considered the result of the aspiration of oral secretions and, as a result, is caused by organisms usually found in the month or gastrointestinal tract (gram-positive cocci, Haemophilus influenzae, or gram-negative enteric bacteria). Late VAP is caused by the same bacteria that frequently cause nosocomial infections in other organ systems (methicillin-resistant Staphylococcus aureus, Pseudomonas aeruginosa, Acinetobacter species, and other gram-negative organisms). Based on the type of organism involved, early VAP is usually the result of aspiration of oral secretions, while late VAP is more likely a result of cross-contamination by poor infection control procedures. Early VAP usually occurs in the first 5 to 7 days of mechanical ventilation and late VAP occurs after this period.

Many of the approaches to VAP surveillance used in the past have been subjective. In 2013, the Centers for Disease Control and Prevention (CDC) established new objective guidelines designing to make the reporting more precise and consistent across institutions.

Historical Approach

Historically, the identification of VAP was not objective. The criteria used were evaluation of chest X-rays, changes in body temperature, white cell count, and the quantity and quality of respiratory secretions. As a result, reported VAP rates varied considerably. Some institutions indicated a zero VAP rate, causing many to question the subjective nature of these criteria. Moreover, the results of VAP surveillance were often not consistent with the diagnosis of VAP used in clinical care of patients.

CDC 2013 Guidelines

In 2013, the National Healthcare Safety Network of the CDC introduced a new surveillance approach for ventilator-associated events (VAEs). A VAE is defined as deterioration in patient's status that may be caused by an iatrogenic event, including not only VAP but also other complications of mechanical ventilation. This tiered approach first identifies ventilator-associated conditions (VACs). If a VAC is present, evaluation for an infection-related ventilator-associated complication (IVAC) is done. If an IVAC is present, evaluation is made for possible or probable VAP. This objective surveillance approach calls for reporting of VAC and IVAC, but not VAP. The intent of these guidelines is to make reporting of VAE an objective approach to compare performance between institutions.

A VAC is an increase in Fio₂ of more than or equal to 0.2 or an increase of more than or equal to 3 cm H₂O positive end-expiratory pressure (PEEP) that is sustained for more than or equal to 2 calendar days after a period of stability (Figure 4-3). The period of stability is defined as more than or equal to 2 calendar days where the Fio₂ and PEEP are stable or decreasing. The period of stability may be at the onset of intubation or any time during the course of invasive ventilation. VAC rate is reportable to external agencies.

There is evaluation for IVAC if VAC criteria are met (Figure 4-4). IVAC occurs on or after day 3 of mechanical ventilation and within 2 calendar days before or after the onset of worsening oxygenation, if both of the following criteria are met: (1) temperature more than 38°C or less than 36°C, or white cell count more than or equal to 12,000 cells/mm³ or less than or equal to 4000 cells/mm³ and (2) a new antimicrobial agent is started and continued for more than or equal to 4 calendar days. IVAC is reportable to external agencies.

If an IVAC is present, there is an evaluation for a possible VAP (Figure 4-5) and probable VAP (Figure 4-6) using quantitative and qualitative microbiologic techniques. The VAP levels of VAE are designed for internal quality improvement initiatives.

VAP bundles (Table 4-1) are used for prevention. The use of a bundle recognizes that a combination of strategies is more effective than a single strategy for VAP prevention.

Hand Hygiene and Related Precautions

The basic tenant of infection control is to ensure that organisms are not transferred from one patient to another. This dictates proper hand hygiene before and after all patient contacts. Gloves should be worn during the patient interaction if there is potential for contact with body secretions. Depending on the infectious condition of the patient, additional precautions such as gown, gloves, and/or a mask may be necessary. Reusable equipment must be cleaned and disinfected appropriately before it is used on another patient.

Care of the Artificial Airway

Orotracheal intubation is preferred over nasotracheal intubation. The cuff on the artificial airway should be inflated to 20 to 30 cm H₂O during exhalation to minimize aspiration of secretions and to minimize tracheal injury. However, even at this pressure, microaspiration can occur through the longitudinal folds in the cuff. To minimize pooling of secretions above the cuff, deep pharyngeal suctioning should be performed on a regular basis and before movement of the patient. Use of endotracheal tubes with subglottic suction ports may reduce the risk of VAP, but care is necessary to prevent occlusion of the suction port. Concern has been raised about the potential for tracheal injury due to the suction and the potential for laryngeal injury due to the rigidity of the tube. Endotracheal tubes coated with silver and the use of devices that scrape the inside of the tube to remove secretions are also available. Newer tapered cuff designs and cuff material (ultrathin polyurethane) may reduce microaspiration. The cost-effectiveness, however, of these newer tube designs and devices is yet to be determined.

Care of the Ventilator Circuit

Ventilator circuits do not need to be changed on a routine basis. Not breaking the circuit is important so that the interior of the circuit is not contaminated. An important part of this practice is use of inline suction catheters. Inline catheters become part of the circuit and do not need to be changed routinely. Any condensate that accumulates in the circuit should be removed away from the patient and from the circuit aseptically. The type of humidification, whether active or passive, does not affect VAP rates. If aerosolized medications are delivered, a device that remains in the ventilator circuit should be used (spacer for metered-dose inhaler, mesh nebulizer, or T-connector with a valve for jet nebulizers). Reusable nebulizers should be rinsed with sterile water (or saline) between treatments and allowed to air dry.

Oral Hygiene

Important to VAP prevention is oral hygiene. The goal is to reduce the bacterial load in the mouth and pharynx. This includes suctioning of the oropharynx, teeth brushing, and the use of chlorhexidine wash.

Noninvasive Ventilation

Use noninvasive ventilation (NIV) when appropriate to decrease the risk of VAP. NIV reduces the risk of VAP because intubation is avoided.

Minimize the Duration of Mechanical Ventilation

The shorter the time that a patient remains intubated, the lower the risk of VAP. Thus, daily spontaneous awaking trials and spontaneous breathing trials should be used to identify extubation readiness. Re-intubation is also associated with VAP risk, so efforts should be used to minimize extubation failure such as the use of NIV in patients at risk.

Positive End-Expiratory Pressure

The use of positive end-expiratory pressure (PEEP) has been shown to reduce VAP rate. The mechanism is that the positive tracheal pressure inhibits microaspiration past the cuff on the artificial airway.

Avoid Unnecessary Transport

Transport of ventilated patients out of the ICU has been shown to increase the risk of VAP. Thus, patient transports for diagnostic tests should be minimized, and care should be taken to avoid contamination of the airway during transport.

Patient Position

Mechanically ventilated patients should be positioned with the head elevated to more than 30 degrees unless there is a contraindication to this position. This is to avoid reflux of gastric contents into the oropharynx and its subsequent aspiration. Some investigators, however, believe that prone position or lateral Trendelenburg position may be more effective in removing secretions and preventing aspiration.

Management of the Gastrointestinal Tract

Reduction of the bacterial load of the gastrointestinal tract affects the risk of VAP. Peptic ulcer prophylaxis is recommended. Appropriate nutritional support should be maintained, but gastric overdistention should be avoided to reduce the risk of regurgitation. Selective decontamination of the gastrointestinal tract has been used in Europe, but this approach has not been widely adopted elsewhere.