Ventilator-associated Pneumonia (VAP)
The definition of VAP is any pneumonia which occurs after 48 hours of invasive ventilation.
How do you know its "ventilator-associated"?
Well. Its not called "ventilator-induced pneumonia", is it.
Pneumonia which occurs in ventilated patients is united into a subgroup of hospital-acquired pneumonia. It is associated with ventilation in the same way as hospital-acquired pneumonia is associated with being in hospital. Ventilation happens to be a common feature of these infections, and being intubated plays a role in its pathogenesis. Question 1c from the first paper of 2000 from the first paper of 2003 discusses VAP in the context of a patient with motor neuron disease. Question 25 from the first paper of 2015 instead asks about some policy changes which might influence a rising trend of VAP incidence.
Incidence of VAP
This 2000 (JAMA) review article puts the incidence at 8 to 28% of mechanically ventilated patients. The mortality from it is around 25 to 50%.
The risk of developing VAP is roughly 3% per day
for the first 5 days of ventilation.
Weirdly, the same article reports that risk falls to 2% per day for days 5 to 10 of intubation, and down to 1% per day for the subsequent days.
Those who develop VAP early tend to do better, and it seems this is because the organisms which cause it in these people are more antibiotic-sensitive. Later VAP tends to be multi-drug resistant.
The likely microbial culprits
The 2005 American Thoracic Society Guidelines describe a menagerie of VAP organisms.
- Pseudomonas aeruginosa
- Staphylococcus aureus
- Escherichia coli
- Klebsiella pneumoniae
- Acinetobacter sp.
In short, its mainly aerobic gram-negatives, with an occasional garnish of MRSA.
Pseudomonas and S.aureus together comprise 50% of the isolated bugs. It is typically a polymicrobial zoo in there. These organisms originate in the oropharynx, as well as the infected biofilm which coats the endotracheal tube.
Certainly, one might be tempted to collect some samples from the lung. Tracheal aspirate culture, BAL sample or PSB (protected specimen brush) - its all the same, it seems the method of sampling really does not influence survival.
Blood cultures should also be collected, but one collects them with the knowledge that the organism cultured from the blood may not represent the organism causing the VAP.
Direct patient care strategies to reduce the risk of VAP
In brief summary, the following are strategies to reduce the risk of VAP, and nosocomial pneumonia in general:
Strongly evidence-based advice
- Early extubation, avoidance of intubation
- Avoidance of reintubation
- Avoid NG tubes
- Use of higher cuff pressures (~ 20cmH2O)
- Use of above-the-cuff subglottic suction
- Minimised sedation and paralysis
- Sit them up to 45° (avoid being supine)
Advice based on weak evidence
- Consider using post-pyloric feeds
- Consider selective digestive decontamination
- Reduce the use of stress ulcer propylaxis.
Don't intubate them. Or, extubate them early.
Obviously, without the huge tube in your larynx, your respiratory defences remain intact, and you stand a lesser risk of developing pneumonia. Is this assertion supported by evidence?
Yes it is.
These guys published a study in JAMA in 2000, where among a series of COPD and pulmonary oedema patients they demonstrated that the risk of nosocomial pneumonia decreased from 22% to 8% by using NIV. They also demonstrated quite a handsome mortality benefit (4% vs 26%) among these patients.
Indeed, this seems to show that intubating patients with COPD actually decreases their survival.
Try not to reintubate them: it increases the risk of VAP.
Avoid NG tubes
Nasogastric tubes create a swamp-like environment in the nasopharynx, and act as a vehicle to deliver nasopharyngeal secretions into the posterior pharynx and down on to the vocal cords. Additionlly, the relaxation of the gastro-oesophageal sphincter results in microaspiration of NG feeds.
In either case, the NGT is associated with increased incidence of VAP.
Cuff pressure and subglottic suction
If you are going to intubate them, keep the cuff pressure up around 20cmH2O, and suction above the cuff. The high cuff pressure supposedly prevents microaspiration of upper tracheal secretions. Similarly, a tube with a subglottic suction port allows for "upper tracheal toilet" and prevents VAP.
Minimise sedation and paralysis
Keep their sedation minimal. Let them cough.
Sit them upright, to 45 degrees.
Supine position just about triples the risk of VAP, specifically in people receiving enteral feeding.
If for whatever reason you need to keep them supine, try to advance the tube beyond the pylorus, for whatever its worth. This has been shown to reduce the incidence of VAP in one controversial study; a meta-analysis which excluded this study had found that there is no increase in the incidence with VAP among NG-fed and NJ-fed patients. Indeed, it appears that enteral feeds (and their intolerance) does not significantly increase your risk of ventilator-associated pneumonia.
Reduce the use of stress ulcer prophylaxis
The use of H1 antihistamines and PPIs has been shown to be an independent risk factor for VAP. Sucralfate seems to reduce the incidence of VAP when compared to ranitidine and antacids (from 21% to 5%)
The selective digestive tract decontamination controversy
The consensus of scholarly opinion is that there is no consensus. Some studies have show a benefit to selectively decontaminating the oropharynx with chlorhexidine mouthwash or a cocktail of antibiotics.
In units with high endemic rates of antibiotic resistance, this is not an effective strategy.
The role of systemic antibiotics is even less clear. However, the published data seems to favour the use of SDD.
There are currently projects in the pipeline which will hopefully put an end to this debate.
The present American Thoracic Society guidelines recommend that although individual trial data is promising regarding selective decontamination (or mouthwashes, or prophylactic systemic antibiotics), their "routine use is not recommended until more data become available"
Antibiotic selection for VAP
My resource for this has been antimicrobe.org.
If they haven't had any antibiotics in the previous month,
its ok to use a monotherapy with a non-antipseudomonal beta-lactam eg. ceftriaxone or amoxycillin-clavulanate.
If they have had some antibiotics recently,
you need to escalate to an antipseudomonal beta-lactam or a carbapenem, eg. tazocin, meropenem, cefepime...
If MRSA is suspected, linezolid is a better choice than vancomycin.
If Legionella is suspected, a fluoroquinolone should be added, as they have better intracellular penetration.
Organisation-level strategies to reduce the risk of VAP
Question 25 from the first paper of 2015 puts the candidate in the shoes of an unit director, asking that they "outline the strategies you would recommend implementing in your unit in an effort to reduce the incidence of VAP." Apart from the direct patient care strategies discussed above (which are mentioned in the college answer) there are also broad policy changes. Unfortunately, the exam candidate needs to also be aware of these. They are unimaginative, and need to be memorised as a list, in case some viva examiner somewhere asks you what you might do in this situation. In the college answer to Question 25, a list of strategies is offered which is quite detailed, and probably represents a 8.0-9.0 mark answer. This list has been dissected, subjected to some scrutiny, and recombined into the table offered below. Probably the best non-college resource for this is a review from Respiratory Care by Crnich et al (2005).
|Strategies||Specific interventions||Rationale and literature support|
According to the abovequoted review (Crnich et al, 2005) this has a modest and shortlived effect on the process of care. Furthermore, most survey respondents (in a 2004 systematic review) felt that they were only sufficiently resourced to disseminated printed material and to hold informal lunchtime meetings.
|Infection control procedures||
The literature in support of this is Standard 3, ACSQHC: this stuff is actually as mandatory as your compulsory annual fire training. The rationale for it is that scupulous attention to infection control might prevent VAP by preventing the transmission of multi-resistant organisms.
Does it help with VAP? Probably,. At least one study (Koff et al, 2011) has found an improvement in VAP after the introduction of a comprehensive hand hygiene program.
The college hastens to add that there "is no high level evidence" to demonstrate that antibiotic stewardship has very much effect on the rates of VAP. In fact some reasonable quality studies do exist (Gruson et al, 2000). The authors were able to decrease both their VAP rates and the incidence of multi-resistant bacteria by starting a program of antibiotic supervision and regular rotation. However, this was a French hospital where the random wanton use of ceftazidime and ciprofloxacin was rampant prior to the study protocol.
This does not refer exclusively to the "terminal cleanining" of a bed space, and is inclusive of the ventilator tubing, the bed itself, the bedside sink, the room air conditioner filter, etc etc. But the bed space is probably the most important: for example, This Irish infection control protocol (2011) cites a brilliant review from Respiratory Care (Crnich et al, 2005). Crnich et al produce a massive table of environmental factors which influence the risk of VAP, including contaminated respiratory equipment, poor ambient air filtration, dislogement of Aspergillus spores during construction activities, and so forth. The review quotes evidence for the importance of these factors among its 388 references.
|Audit of activities||
Is there a point to this? To many it seems like pointless busywork. Indeed, a widely cited 2004 meta-analysis (Grimshaw et al, 2004) found that "the effect of audit and feedback on improving professional practice was small to moderate", and that "variability in the study quality and reporting transparency makes it difficult to recommend widespreaduse of audit and feedback". This was not specific to infection control, but pertaining to the broader tendency of healthcare staff to spontaneously self-organise into committees and auditing bodies.