An Update on Preventing Ventilator-Associated Pneumonia in Adults

Ventilator-Associated Pneumonia

Ventilator-associated pneumonia (VAP) is the onset of pneumonia at least 48 hours after a patient is intubated. It is the endotracheal tube, rather than the need for mechanical ventilation, that leads to VAP. VAP causes more death than any other healthcare-associated infection, exceeding the rate of death from central line infection, sepsis, and respiratory tract infection in nonintubated patients.[1] Mortality varies according to the type of organism causing VAP and is highest when pneumonia is caused by multidrug-resistant organisms.[2]

Between 10% and 20% of patients intubated for more than 48 hours will develop VAP.[3] VAP complicates recovery and extends the duration of mechanical ventilation. Length of hospital stay is significantly longer in VAP patients, who incur at least $10,000 and as much as $40,000 in additional hospital costs.[1,3] VAP is no longer considered an inevitable consequence of treatment; it is now considered a preventable healthcare error.[4]
Pathogenesis of VAP

Of all the plausible mechanisms through which bacteria can reach the lower respiratory tract, the most likely is micro- or bolus aspiration of oropharyngeal organisms.[1] Hospitalized patients have high rates of oropharyngeal or tracheobronchial colonization with Gram-negative bacilli.[1] Subglottic pooling of these secretions with leakage around the endotracheal tube cuff is the primary route of bacterial entry.[5] Bacteria from the dorsal tongue are also frequently found in the lungs of patients with VAP.[6] Gastric colonization with translocation into the respiratory tract, proposed as another route of pulmonary infection, is not believed to be as important as oropharyngeal colonization.[1,7]

There is no shortage of disease-causing bacteria in the typical patient care environment. The hands or clothing of caregivers, dust, air, and water can all convey microorganisms.[7] Bacteria can gain entry to the respiratory tract when bacteria-laden aerosols or ventilator circuit condensate are inhaled through the endotracheal tube.[1] Contaminated nebulizers used to provide airway humidification can transmit bacteria by the aerosol route. Endotracheal suctioning procedures can introduce bacteria from equipment or caregivers' hands.[5]

Evidence-Based Prevention of VAP

In consideration of our current shortage of nurses and consequent heavy workloads, we cannot afford to adopt new practices unless they are evidence based. Intuitive or traditional interventions, however much sense they make or how long we have performed them, no longer have a place in patient care. Because VAP is such a serious problem, many studies have documented the effectiveness (or ineffectiveness) of various interventions designed to prevent VAP, supplying the evidence base that nurses require. However, in spite of an abundance of experimental data demonstrating that VAP can be prevented, the gap between knowledge and practice remains wide.

Evidence-based guidelines can serve as a catalyst for knowledge translation to the clinical arena.[8] In addition to reducing the overall length of time that patients are intubated, strategies to prevent VAP arise directly from the 3 mechanisms believed to cause VAP: microaspiration of colonized secretions, colonization of the digestive tract, and exposure to contaminated hands or equipment.[9]
Reduce the Duration of Ventilation

The risk of VAP increases with each day the patient is intubated.[10] The best and most obvious way to prevent pneumonia in critically ill patients is to avoid intubation altogether and implement noninvasive ventilation whenever possible.[7,9] When an endotracheal tube is necessary, unplanned extubation and reintubation must be avoided, because reintubation increases the risk for VAP.[11]

Daily assessment and documentation of patient readiness to wean from mechanical ventilation and daily interruption of sedative infusions (sedation vacations) have resulted in shorter duration of mechanical ventilation and length of stay.[12,13] These 2 distinct interventions are often combined, as they are interdependent in practice.[13] Effective ventilator weaning requires the cooperation of the patient; therefore, in adults, sedation must be lightened before weaning is attempted.[14]

A sedation vacation with spontaneous breathing trial typically involves lightening sedative infusions long enough to achieve alertness (responsive to commands) in the patient, but before anxiety and restlessness set in. The patient is tested for spontaneous breathing capacity and assessed for readiness to wean from mechanical ventilation, and results are documented. The risks of interrupting sedative infusions include spontaneous extubation, pain, anxiety, dyssynchrony with mechanical ventilation that results in arterial desaturation, and unknown effects of arousing patients and then putting them back to sleep.[15] Patients must be closely observed throughout these procedures, and steps must be taken to prevent self-extubation.[14]

If sedation is to be continued following the weaning attempt, the dose is generally reduced, often to half of the original infusion rate. Many facilities use sedation scales, such as the Riker, to avoid oversedation.[12,16]
Prevent Microaspiration of Secretions

The normal human mouth contains hundreds of bacteria species, but these are continually flushed from the oral cavity by saliva production and swallowing. An estimated 100-150 mL of oral secretions can accumulate in the adult mouth in a 24-hour period.[17] The intubated patient who receives nothing by mouth produces very little saliva. The mouths of critically ill patients can become colonized as quickly as 24 hours following admission. Virulent bacteria can proliferate and, if unchecked, will build up in the form of dental plaque, a reservoir of bacteria. Secretions that pool in the aerodigestive tract above the endotracheal tube cuff can be aspirated into the lungs, causing pneumonia. This mechanism is supported by findings that, in the majority of intubated patients, the bacteria colonizing the mouth and the lungs are the same.[1] Although all intubated patients are at risk of developing pneumonia by this route, patients with neurologic disease are even less able to protect their own airways, making them highly prone to aspiration of oral secretions.[18]

Both intermittent and continuous suction of subglottic secretions have been shown to decrease VAP rates by preemptively removing the source of infection.[19] Intermittent suctioning of the oral cavity before a position change can significantly reduce the incidence of VAP, number of days on mechanical ventilation, and length of intensive care unit (ICU) stay.[20,21] Continuous aspiration of subglottic secretions, although more expensive, achieves greater protection against VAP.[22] Subglottic secretion drainage is an evidence-based preventive measure, yet it is not widely practiced. In a survey of 719 US hospitals, only 21% reported using subglottic secretion drainage.[23]
Oral Hygiene

Oral care has traditionally been a low priority in the care of critically ill, ventilated patients. Nurses may view oral care primarily as a comfort measure or lack conviction that oral care makes a difference in VAP.

Frequent, thorough oral hygiene can reduce colonization of the teeth, tongue, and gums. Significant reductions in VAP have occurred when oral care is performed consistently and meticulously. In one study that compared tooth brushing every 8 hours with routine oral care for intubated patients, an immediate, dramatic drop in VAP rate to 0 occurred in the intervention group.[18]

The American Association of Critical Care Nurses has developed a guideline for oral hygiene in the critically ill patient. The basic elements of this protocol include oral assessment; brushing teeth, tongue, and gums with a soft toothbrush (at least twice daily); application of moisturizing agents to the oral mucosa and lips; and an antiseptic rinse in selected patients.[24] Simple foam-tipped dental swabs do not remove plaque as efficiently as toothbrushes or specially designed oral care systems.[25] Some facilities use a suction toothbrush, a Yankauer suction device with a toothbrush end, to clean and suction the oral cavity at the same time. Wearing gloves during suctioning minimizes the introduction of bacteria from the caregiver's hands.

Oral decontamination with chlorhexidine reduces oropharyngeal colonization and has been successfully used to prevent VAP, particularly in cardiac surgery patients.[26] The extra costs for oral care supplies such as oral care kits or suction toothbrushes are easily offset if a single case of VAP is prevented.
Endotracheal Tube Care

Formation of an endotracheal tube biofilm, permitting bacteria to accumulate and persist, may play a contributory role in the development of VAP, especially in late-onset infection. Silver- and antiseptic-impregnated endotracheal tubes show promise in reducing this colonization.[7] Most experts recommend using orotracheal tubes, rather than nasotracheal tubes, because the latter can increase the risk of sinusitis, a likely precursor to VAP.[19] Attention to proper endotracheal tube cuff pressure in adults (at least 20 cm H2O but no greater than 30 cm H2O) is also important to prevent oral secretions from migrating into the lungs.[19]

The endotracheal tube should have an evacuation lumen proximal to the cuff for intermittent or continuous subglottic suctioning.[9] Neither research nor guidelines have, to date, determined conclusively that closed suction systems are preferred over open systems for suctioning endotracheal tubes.[27]

Other Evidence-Based Approaches to VAP Prevention
Maintain a Semirecumbent Position

Head-of-bed elevation reduces the risk for aspiration of oro- and nasopharyngeal secretions, thereby reducing the risk for VAP.[1] A randomized controlled trial comparing semirecumbent and supine position in mechanically ventilated patients was halted early when data analysis revealed that the semirecumbent position was superior in preventing VAP.[28] The advantage was greatest for patients receiving enteral nutrition. This study and others have led to the recommendation to elevate the bed of mechanically ventilated patients, if not contraindicated by patient condition, to a 30° to 45° angle. In spite of some evidence that this degree of elevation does not prevent tracheal colonization,[29] it remains a common VAP prevention recommendation. Additional potential benefits of bed elevation are reducing the risk of aspirating gastrointestinal contents and improving spontaneous ventilation.[14]

Keeping patients in the desired upright position can be difficult to achieve in practice. In one multicenter study, the target backrest elevation of 45° was achieved only 85% of the time, and the maximum achieved elevation of 28° failed to prevent VAP.[30] In another study, beds intended to be elevated to 30° were actually at 19°, on average, and many patients were found in the supine position.[31] Angle indicators on hospital beds are often small, poorly located, and difficult to read.[32]

Williams and colleagues[32] introduced a simple, easy-to-view, and easy-to-interpret angle indicator that displayed, from as far away as the doorway of the patient's room, whether the head of the bed was adequately elevated.[32] During a control period prior to introducing the new angle indicator, head-of-bed elevation averaged 21.9° ± 9.1°. Using the new angle indicator, bed angles averaged 30.9° ± 7.5° (P < .005). Compliance with proper head-of-bed elevation improved from 23% without to 72% with the angle indicator device.
Increase Patient Mobility

Immobility contributes to the development of VAP. In the immobile patient, secretions and mucus tend to pool, secretions are harder to expel, and overall pulmonary functioning declines. Increasing the mobility of a ventilated patient, however, is not a simple task. Linda Greene, RN, MPS, CIC, emphasizes the benefits that can be attained by increasing patients' mobility, even marginally. Greene is lead author of a new guide for preventing VAP that is currently being developed by the Association for Professionals in Infection Control and Epidemiology (APIC). As one component of an overarching initiative known as Targeting Zero, the VAP elimination guide (available in summer 2009) will assist hospitals in their efforts to prevent VAP by outlining a comprehensive, evidence-based prevention program.

"Mobility promotes weaning and, therefore, may shorten length of ICU stay," advises Greene. In Targeting Zero, mobility interventions are suggested for each stage of a patient's disease course. A mobility protocol is essentially an algorithm for advancing patients' degree of mobility, from repositioning, to sitting up, to standing at the side of the bed. "Nurses aren't always comfortable with mobility protocols for these critically ill patients," acknowledges Greene. "But just because the patient has a tube doesn't mean the patient can't sit up on the side of the bed or even ambulate."

Even basic interventions such as repositioning, although challenging, are extremely important in the prevention of VAP. Some hospitals have purchased kinetic beds, which continually rotate the patient's body, reducing the effect of stagnating secretions. Evidence to date indicates that kinetic beds may reduce VAP, but the cost and other complications associated with these beds may be significant barriers to their widespread use.[19,33]
Control Gastric Secretions

Clinically important aspiration of gastric contents usually occurs in patients who have one or more of the following conditions, common in mechanically ventilated patients: a depressed level of consciousness, dysphagia due to neurologic or esophageal disorders, an endotracheal tube, tracheostomy, indwelling enteral tube, or ongoing enteral feeding.[1] An indwelling enteral tube may increase nasopharyngeal colonization, cause reflux of gastric contents, or allow bacterial migration via the tube from the stomach to the upper airway. Contamination of the enteral solution during its preparation may also lead to gastric colonization.

The semiupright position used to prevent aspiration of oral secretions also serves to prevent gastric reflux leading to aspiration. Gastric overdistention must also be avoided.[9] Whether routine digestive tract decontamination and avoidance of H2 agonists and protein pump inhibitors should be included in VAP prevention protocols remain unresolved issues.[9]
Prevent Contamination of Equipment

Any reusable respiratory device can become contaminated and introduce pathogens to the respiratory tract.[19] The Healthcare Infection Control Practices Advisory Committee offers a set of detailed instructions for cleaning and maintaining medical equipment, including respiratory care equipment. Reusable respiratory equipment must be disinfected, sterilized (as appropriate), and stored properly.[9] Sterile water should be used to rinse reusable equipment.[9] The frequency of ventilator circuit changes has no effect on VAP rates, so changing ventilator circuits routinely only adds to the cost of care. Instead, ventilator circuits should be changed when they are visibly soiled. Condensate should be drained regularly from ventilator tubing (without opening the circuit) and prevented from flowing into the patient's endotracheal tube.[9]

Evidence suggests that the use of heat and moisture exchangers (except where contraindicated), rather than heated humidifiers, can reduce the incidence of VAP because they generate less condensate.[19] If used, these devices should be changed weekly.[8]

Ventilator Bundles

A care "bundle" is a set of evidence-based clinical practices that individually improve care and, when combined, magnify improvement.[14] The scientific evidence for each element of a bundle is sufficient for that element to represent a standard of care.[14] The Institute for Healthcare Improvement's (IHI) ventilator bundle combines 4 components of care: elevating the head of the bed, daily sedative interruption and assessment of readiness to extubate, peptic ulcer disease prophylaxis, and deep vein thrombosis prophylaxis.[14] The ventilator bundle was initially designed as an overall strategy to improve care of ventilated patients, not necessarily to prevent VAP. However, many hospitals documented a reduction in VAP rates (by an average of 45%) following implementation of the bundle. When teams in some facilities unfailingly apply every bundle element on every patient every time, they have experienced months without a single case of VAP.[14]

The IHI ventilator bundle is not intended to be a comprehensive plan of care to prevent VAP. The IHI recognizes that oral care, subglottic suctioning, gut decontamination, and continuous lateral rotation are also important preventive strategies.[14] Many hospitals have added one or more of these strategies to their VAP prevention protocols. Care should be taken to avoid overly extensive care bundles, because care bundles are most effective when the number of elements is small.[14] The IHI emphasizes that implementing the ventilator bundle requires planning and takes time; it will not be achieved overnight.[14] Recommendations for how to implement and evaluate the ventilator bundle, including useful documentation forms, are available online from the IHI.

Other VAP prevention bundles have been published as well. A bundle of interventions collectively known as FASTHUG (daily evaluation of feeding, analgesia, sedation, thromboembolic prophylaxis, elevation of the head of the bed, ulcer prophylaxis, and glucose control), consistently applied for 2 years, led to a significant drop in VAP (from 19.3 to 7.3 per 1000 ventilator days) among surgical intensive care patients.[34]

Some experts recommend going "beyond the bundle," and employing other evidence-based processes that may lead to a zero VAP rate. Linda Greene emphasizes that hospitals should first "hardwire the basics," such as compliance with handwashing, and then gradually incorporate evidence-based practices into the routine standard of care. "Measure your basic processes, such as head-of-bed elevation, hand hygiene, and oral care, first," suggests Greene. "If you're not doing well there, introducing advanced, extensive protocols will not be successful."

Teamwork, Collaboration, and Feedback

It may not be just the individual interventions, or even a combination of interventions, that achieves the reduction in VAP. When evidence-based interventions or bundles are implemented through teamwork and collaboration, it could be this new emphasis on working together toward common goals that actually drives the improvements.[14]

Respiratory therapists are important members of the team in the prevention of VAP, as they work side by side with nurses in patient care and are largely responsible for the maintenance and handling of respiratory equipment. The respiratory therapist also strives, along with the nurse, to maintain patients in semirecumbency, to conduct daily assessments of readiness to wean, and to maintain airway humidity. To address antibiotic stewardship, an initiative that reduces VAP by preventing the emergence of multidrug-resistant organisms, collaboration with physicians, pharmacy, and infection control professionals is also required.[35]

"It's not enough to have a policy about preventing VAP," cautions Greene. "It needs to be consistently implemented and measured, with feedback given to caregivers to improve processes." Greene describes 2 types of professionals in the ICU setting, the "early innovators" and the "laggards," both individuals who can influence success or failure. "You need to identify your early innovators, the ones who move ahead quickly and achieve success, and then spread their successes by engaging the others." Dissemination of results must occur on a regular basis. "Nurses want to know how well they are doing," explains Greene.

Deterrents to VAP Prevention

It is well known that staffing shortages and heavy workloads impede the nurse's ability to comply with basic hygiene and infection control measures. Low nurse staffing and low nurse-to-patient ratios have been shown to increase the risk for late-onset VAP.[36] Fear of change, communication failures, poor teamwork, and partial buy-in on the part of nurses, physicians, and respiratory therapists are other possible impediments to successfully implementing a VAP prevention protocol. A lack of understanding of the principles underlying recommended practices can also contribute to failure of protocols to produce results.

Studies of intensive care nurses' knowledge and implementation of evidence-based guidelines for preventing VAP are not universally encouraging.[37,38] Many nurses and respiratory therapists do not know the rate of ventilator-associated pneumonia in their units.[17,39] Although both nurses and respiratory therapists self-report high rates of utilization for some evidence-based VAP practices, other practices, such as subglottic suctioning and routine drainage of ventilator condensate, may be less often performed.[39] In survey research by Ricart and colleagues,[40] reported nonadherence to evidence-based guidelines for preventing VAP on the part of physicians and nurses was surprisingly high. Cason and colleagues[17] found inadequate rates of handwashing, glove wearing, subglottic suctioning, oral hygiene, and head-of-bed elevation among intensive care nurses.

Furthermore, both nurses and respiratory therapists report fairly high rates of adherence to ineffective interventions, such as such as routine circuit changes, in-line suction catheter changes, or chest physiotherapy. Time spent on ineffective interventions is time taken from proven interventions.

Therefore, in addition to a supportive culture, adequate staffing, and ample resources, education for all team members and the development of specific protocols and order sets for the prevention of VAP are critical. Ideally, the individuals who will be implementing these protocols and order sets should be involved in their creation.[40] Healthcare professionals who understand the reasons behind the protocols are much more likely to be dedicated to following them.[41] An evidence-based education program regarding oral care, for example, improved oral care compliance and reduced one unit's VAP rate by 50%.[42] Education sessions as short as 30 minutes can improve infection control compliance.[43]
The Bottom Line

VAP is a patient safety concern that can be prevented with evidence-based interventions. Lessening VAP rates will shorten hospitalization and reduce morbidity, saving lives as well as money. Innumerable resources exist to aid individuals and units to improve their understanding of VAP and to apply preventive strategies in critical care.

References

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