Ventilator-associated pneumonia is a potentially fatal lung infection which may afflict hospital patients who have been placed on a mechanical ventilation breathing machine (also known as endotracheal intubation.)
VAP may occur 48-72 hours after a patient is intubated, and is the result of a number of interplaying factors. Approximately half of all hospital-acquired pneumonia cases can be attributed to VAP. Experts estimate that 9-27% of mechanically ventilated patients will develop VAP, accounting for roughly 50% of all antibiotics administered in ICUs. The malady carries a 20-30% death rate. The risk of infection is greatest in the 5 days following initial intubation. Although it is still a formidable menace for intubated patients, preventative techniques and other best practices have contributed to a decline in the rate VAP cases over the last century.
VAP is the result of a microorganism invading the lungs and disturbing the ling micro biome. It is distinct from community-acquired pneumonia in that it is almost exclusively caused by an invasive species of bacteria, while CAP can be caused by viruses, fungi and bacteria alike. That being said, any microorganism that causes CAP may also cause VAP, but VAP is more commonly (and distressingly) caused by multi drug resistant bacteria.
- Pseudomonas aeruginosa
- Klebsiella pneumoniae
- Serratia marcescens
- Stenotrophomonas maltophilia
- Burkholderia cepacia
- Methicillin-resistant Staphylococcus aureus (MRSA, a multidrug resistant form of the ‘staph' bacteria)
It is believed that VAP is a result of the free passage of bacteria to lower lung segments, made possible by the endotracheal tube. Patients undergoing chemotherapy or who are malnourished experience certain deficiencies of the immune system which make it easier for bacterial invaders to strike. By colonizing the tube itself, with each breath the patient takes bacteria are lodged in the blood vessels of the lungs, causing a blockage.
This is one theory. It is also possible that certain disease-causing bacteria already in the exist in the mucus lining of the individual's bronchial tree, kept in check by the body's immune system. After intubation, a build up of fluids may prevent airway clearance allowing the bacteria to colonize. These bacterial droplets are then wafted into the lung fields.
Symptoms of Ventilator-Associated Pneumonia
There is poor specificity with regard to the symptoms of VAP.
- Cough with pus-like or greenish phlegm
- Fever and chills
- Shortness of breath
- Sharp chest pain, worsened by deep breaths or coughs
- Decreased blood pressure
- High heart rate
- Loss of appetite
- In the elderly, first signs may be mental changes and confusion
The treatment of VAP hinges on a proper diagnosis, seeing as treatment need be matched to the causative bacteria/other microorganism. Diagnostic methods for the disease have proven difficult to formulate, as they have not yet been standardized. Typically, a combination of lab evidence, clinical symptoms and radiographics are used in the diagnosis of VAP. The CDC has outlined certain suggested diagnostic criteria
- Temperature greater than 38C or less than 36C
- White blood cell count greater than 12,000/mm3 or less than 4,000/mm3
- Purulent secretions, increased secretions, or change in secretions
- Positive tracheal cultures or bronchoalvelolar lavage cultures
- Some sign of respiratory distress, such as shortness of breath, rapid breathing, abnormal breathing sounds when listening with stethoscope
- Increased need for oxygen on the ventilator
- Chest X-Rays: at least two serial xrays showing sustained or worsening shadowing (infiltrates or consolidations)
- Positive cultures obtained directly from lung environment, such as from the trachea or bronchioles
Initially, if a health care provider suspects VAP, broad-spectrum antibiotics may be administered the to the patient until the exact causative bacteria and its antibiotic sensitive are successfully determined. Selection of the proper antibiotic also depends on the duration of the patient's ventilation. Broad spectrum antibiotics may be used for later onset VAP (>4 days), while limited antibiotics are better suited to early onset cases. The most common cause of VAP, P. aeruginosa has proven resistant to “mono therapy” or therapy with just one antibiotic, therefore combination therapy is ever encouraged. Earlier cases of VAP demonstrated a trend wherein multi drug resistant bacteria were associated with later onset cases while earlier cases were not. However, recent evidence increasingly shows multi drug resistant bacteria in earlier cases as well.
As the most common lethal infections observed in ICUs, special attention must be paid to risk factors of VAP. The presence of certain risk factors, the virulence of the invasive bacteria and the patient's immunity all play a key role in the development of ventilator associated pneumonia. Because the endotracheal tube inhibits certain bodily defense mechanisms like the cough reflex, the tube is the single greatest risk factor in developing VAP.
The severity of the patient's preexisting illness also plays a role. If they are recovering from recent surgery or have had considerable antibiotic exposure in the past, they may be at greater risk of developing VAP.
General risk factors include:
- Age greater than 60 years
- Head trauma
- Patient being male
- Transportation out of ICU
- ICP monitor
- Use of antacids
- Use of sucralfate
- Use of Antibiotics
- Receipt of Enteral Nutrition
Preventing VAP in Hospitals
With some estimations placing the mortality rate of VAP as high as 50%, it is critical that exceptional care be taken with preventing the development of the disease in ventilated patients. Efforts to prevent VAP should begin at initial intubation and last until just after its conclusion. Simple nursing interventions can greatly reduce the incidence of early onset VAP, although it is generally recognized that little can be done to reduce the incidence of late onset VAP. Although a fair amount of data has accumulated surrounding interventions and guidelines to reduce VAP, government-sponsored statistics show that compliance with these guidelines among hospital staffs is lacking (falling between 30 and 64%.)
The primary focus should be given to modifiable risk factors, as certain factors such as pre-existing health conditions, surgical recovery, age, bodily trauma, and immunodeficiencies cannot be tackled in the same manner.
Prior to Intubation
Reversible causes of respiratory failure such as fluid balance, sedation, analgesia, and bronchospasm should be addressed. Non-invasive mechanical ventilation (NIV) has proven better than endotracheal intubation with regard to patient morbidity and is likely the more favorable method, however, physicians have exhibited reluctance toward NIV due to the increased resource consumption and patient intolerance.
Process of Intubation
During the intubation process, the nurse should take care to avoid gastric over distention and opt for oral intubation over nasal intubation, as the latter has a greater association with VAP and sinusitis.
With gastric tubes inserted via an oral route, the head of the bed should be elevated by 30 to 45 degrees. All those handling items for the patient should practice good hand hygiene. Transportations out of the ICU should be minimized. Heat and moisture exchangers (HMEs) should be changed every 48 hours - although less frequent changes may be associated with a reduction in VAP risk, they are necessary for monitoring for trapped secretions or other airway obstructions. Sedation should be minimized to reduce the overall duration of mechanical ventilation.