What is ventilator-associated pneumonia?

What is ventilator-associated pneumonia?

 

Ventilator-associated pneumonia (VAP) is a lung infection that develops in a person who is on a ventilator. It is defined as pneumonia that occurs 48 to 72 hours or thereafter following endotracheal intubation, characterized by the presence of a new or progressive infiltrate, signs of systemic infection (fever, altered white blood cell count), changes in sputum characteristics, and detection of a causative agent.

 

A ventilator, also known as a mechanical ventilator or breathing machine, is a machine that is used to help a patient breathe by giving oxygen through a mask or a breathing tube placed in a patient’s mouth or nose, or through a hole in the front of the neck. An infection may occur if pathogens enter through the breathing tube and get into the patient’s lungs.

 

VAP contributes to about half of the hospital-acquired pneumonia cases and approximately 10% of mortality (which, however, varies considerably for different kinds of patients). In contrast to other types of hospital acquired infections such as those involving the urinary tract or skin, the mortality rate for VAP is much higher. It poses grave implications in endotracheally intubated adult patients in ICUs worldwide, leading to extended use of mechanical ventilation while  increasing the use of antimicrobials, length of hospital stays and direct medical costs.

 

What is the cause of VAP?

 

A patient diagnosed with respiratory failure (in other words, difficulties in breathing or getting enough oxygen into the blood) may be put on a ventilator. While ventilators are designed to relieve patients’ breathing problems, they also increase the risk of contracting pneumonia by making it easier for pathogens to enter patients’ lungs.

 

The use of breathing tube (endotracheal tube) is the most important risk factor for VAP because it interferes with the natural defense mechanisms of the respiratory tract (the cough reflex of glottis and larynx) and prevents effective coughing. Aspiration of oropharyngeal pathogens or leakage of bacteria around the endotracheal tube cuff is the primary route of bacterial entry into the trachea.

 

Overall, pathogens causing pneumonia can get into the lower respiratory tract directly through microaspiration, the development of a bacterial biofilm within the endotracheal tube, pooling and trickling of secretions around the cuff and impairment of mucociliary clearance of secretions within the airways. The longer the duration of ventilation, the greater the risk of developing VAP.

What pathogen causes VAP?

 

VAP may be caused by a variety of pathogens and they are often bacteria. The predominant ones are Staphylococcus aureus, Pseudomonas aeruginosa, and Enterobacteriaceae, but the type usually depends on the duration of mechanical ventilation.

 

Typically, bacteria causing early-onset VAP include Streptococcus pneumoniae (as well as other streptococcus species), Hemophilus influenzae, methicillin-sensitive Staphylococcus aureus (MSSA), antibiotic-sensitive enteric Gram-negative bacilli, Escherichia coli, Klebsiella pneumonia, Enterobacter species, Proteus species and Serratia marcescens. Late VAP are typically caused by multidrug-resistant bacteria, such as methicillin-resistant S. aureus (MRSA), Acinetobacter, Pseudomonas aeruginosa, and extended-spectrum beta-lactamase producing bacteria (ESBL).

 

How do you detect VAP?

 

Detecting VAP is challenging because the clinical, radiographic, and microbiological criteria for surveillance are subjective and nonspecific. For example, systemic signs of infection (such as fever, tachycardia, and leukocytosis) are one of the components used for the diagnosis, but these findings are neither specific nor conclusive because they can be caused by any condition that releases cytokines.

 

In light of the fact that VAP is a frequent and serious cause of morbidity and mortality in healthcare settings, the Centers for Disease Control and Prevention (CDC) in the United States developed a more comprehensive approach for the surveillance of patients put on mechanical ventilator. The new criteria broaden the scope from pneumonia alone to include other ventilator-associated events with an aim to making surveillance more objective and to improving outcomes for mechanically ventilated patients.

 

For more information, see here.

 

How common is VAP?

 

According to a journal article published in 2014, VAP contributes to approximately half of the hospital-acquired pneumonia cases and it is estimated to occur in 9 to 27% of the mechanically ventilated patients. It is the second most common nosocomial infection in the intensive care unit (ICU) and the most common in mechanically ventilated patients. VAP rates range from 1.2 to 8.5 per 1,000 ventilator days and are reliant on the definition used for diagnosis. Risk for VAP is highest during the first five days of mechanical ventilation. Earlier studies show that the mortality rate was between 33 and 50%, but it is highly variable depending on the underlying medical condition. The attributable risk of death has decreased to an estimate of 9 to 13% over the years, mainly due to the implementation of preventive strategies. Approximately 50% of all antibiotics administered in ICUs are for the treatment of VAP.

 

How long does VAP last and how is it treated?

 

VAP can be treated with antibiotics. The choice of antibiotics depends on the pathogens causing the infection, the duration of mechanical ventilation, clinical setting, information provided by direct examination of pulmonary secretions, and intrinsic antibacterial activities of antimicrobial agents and their pharmacokinetic characteristics.

 

Early onset VAP (≤ 4 days) can be treated with limited spectrum antibiotics whereas late onset VAP (> 4 days) requires broad spectrum antibiotics. It has been reported that early effective treatment for VAP is associated with reduced mortality. On the other hand, delays in the initiation of appropriate antibiotic treatment may lead to a higher mortality rate. Accordingly, rapid identification of infected patients and timely administration of appropriate antibiotics are very important for better outcome.

 

The usual duration of treatment for early-onset VAP is eight days or longer in the case of late-onset VAP or if multidrug-resistant pathogens are suspected or identified.

 

From patients’ perspective, it is important to follow the prescribed treatment plan. It may take time to recover from pneumonia. Some people feel better and are able to return to their normal routines in one to two weeks. For others, it can take a month or longer. Most people continue to feel tired for about a month.

 

How can VAP be prevented?

 

According to the CDC, some of the measures taken by hospitals (including doctors, nurses, and other healthcare providers) to prevent VAP include the following:

• Keep the head of the patient’s bed raised between 30 and 45 degrees unless not allowed by other medical conditions.
• Check the patient’s ability to breathe on his or her own every day so the patient can be taken off of the ventilator as soon as possible.
• Clean their hands with soap and water or an alcohol-based hand rub before and after touching the patient or the ventilator.
• Clean the inside of the patient’s mouth on a regular basis.
• Clean or replace equipment between use on different patients.

 

On the other hand, patients and their family members can do the following to help prevent VAP:

 

Patients

• Quit smoking – patients who smoke get more infections. Seek information about how to quit before surgery.
• If healthcare providers do not clean their hands, ask them to do so.

 

Patients and Family Members

• Ask about raising the head of the bed.
• Ask when the patient will be allowed to try breathing on his or her own.
• If healthcare providers do not clean their hands, ask them to do so.
• Ask about how often healthcare providers clean the patient’s mouth.

 

Takeaway

 

VAP is one of the healthcare-associated infections (HAIs) which occurs frequently in the ICU. It may lead to serious outcome, longer hospital stays and higher healthcare costs for patients. The mortality rate is higher than other types of HAIs such as those involving the urinary tract or skin. The diagnosis of VAP has been challenging because the lack of sensitivity or specificity in the criteria for identification. To address this issue, the CDC has published new guidelines for the surveillance of mechanically ventilated patients in order to make the identification criteria more objective.

 

There are some measures that can be taken to lower the risks of contracting VAP and it has been reported that early effective treatment can reduce mortality rate significantly. Therefore, the most important thing for infected patients is to receive timely and appropriate medical therapy so that better outcome may be achieved.

 

Reference

1. Chastre, J., & Fagon, J. Y. (2002). Ventilator-associated Pneumonia. American Journal of Respiratory and Critical Care Medicine, 165(7), 867–903. https://doi.org/10.1164/ajrccm.165.7.2105078
2. Frequently Asked Questions about Ventilator-associated Pneumonia. (2019). US Centers for Disease Control and Prevention. https://www.cdc.gov/hai/vap/vap_faqs.html
3. Guidelines for the Management of Adults with Hospital-acquired, Ventilator-associated, and Healthcare-associated Pneumonia. (2005). American Journal of Respiratory and Critical Care Medicine, 171(4), 388–416. https://doi.org/10.1164/rccm.200405-644st
4. Kalanuria, A. A. (2014, March 18). Ventilator-associated pneumonia in the ICU – Critical Care. BioMed Central. https://ccforum.biomedcentral.com/articles/10.1186/cc13775
5. Klompas, M., Branson, R., Eichenwald, E. C., Greene, L. R., Howell, M. D., Lee, G., Magill, S. S., Maragakis, L. L., Priebe, G. P., Speck, K., Yokoe, D. S., & Berenholtz, S. M. (2014). Strategies to Prevent Ventilator-Associated Pneumonia in Acute Care Hospitals: 2014 Update. Infection Control & Hospital Epidemiology, 35(8), 915–936. https://doi.org/10.1086/677144
6. Koenig, S. M., & Truwit, J. D. (2006). Ventilator-Associated Pneumonia: Diagnosis, Treatment, and Prevention. Clinical Microbiology Reviews, 19(4), 637–657. https://doi.org/10.1128/cmr.00051-05
7. Pneumonia. (n.d.). National Heart, Lung, and Blood Institute. https://www.nhlbi.nih.gov/health/pneumonia
8. Ventilator/Ventilator Support. (n.d.). National Heart, Lung, and Blood Institute. https://www.nhlbi.nih.gov/health-topics/ventilatorventilator-support