VAP Flashcards
The Clinical Pulmonary Infection Score (CPIS) was developed by
Pugin and colleagues7 to facilitate the diagnosis of VAP using clin-
ical variables. It gives a score of 0–3 for temperature, leucocytosis,
PaO2 =FIO2 ratio, chest radiography, tracheal secretions, and
culture of tracheal aspirate. The maximum score that can be
obtained is 12 and a score >6 is diagnostic of VAP. The assessment
of the CPIS score is prone to considerable inter-observer variabil-
ity, particularly with regard to interpretation of the tracheal
secretions and the chest X-ray (CXR).
The United States Centre for Disease Control (CDC) definition8
was designed as a surveillance tool for HAI but has been used in
the diagnosis of VAP. It was not meant for the diagnosis of pneu-
monia, neither is it specific for VAP. However, it has been shown
to have good sensitivity and positive predictive value, but its low
specificit
The Johannson criteria diagnosed a VAP based on the pres-
ence of new or progressive infiltrates on the CXR associated
with at least two of three clinical features—leucocytosis, puru-
lent secretions, temperature >38°C. Diagnosis by these criteria
was compared with immediate post-mortem lung biopsies; the
sensitivity was only 69%, while the maximum specificity was
75%.5
The HELICS6 criteria are used for VAP surveillance in Europe.
These again rely on a combination of clinical, radiological, and
microbiological criteria and classify the pneumonia from PN1 to
PN5 based on the microbiological method used. PN1 refers to
diagnosis by minimally contaminated lower respiratory tract
(LRT) specimens (BAL, PBS, distal protected aspirates), while
PN4 refers to positive sputum culture or to non-quantitative
LRT aspirates such as tracheal aspirates. Therefore, a unit’s VAP
rate can vary significantly depending on the microbiological
method used.
The main pathogenic factor in the development of VAP is biofilm
formation within the tracheal tube (TT) and microaspiration of
secretions. The presence of a TT interferes with the normal pro-
tective upper airway reflexes and prevents effective coughing.
The oropharynx becomes rapidly colonized by aerobic gram-
negative bacteria after illness, antibiotic administration, and hos-
pital admission. These contaminated secretions pool above the
TT cuff and slowly gain access to the lower airway through a
fold in the wall of the cuff. A bacterial biofilm, which is impervi-
ous to antibiotics, gradually forms on the inner surface of the
tube and serves as a nidus for infection. This pathogen-rich bio-
film is pushed into the distal airways by ventilator cycling and in
the setting of immunosuppression associated with critical illness
causes pneumonia. The longer the duration of ventilation, the
greater the risk of developing VAP. Nursing patients in a supine
position increases the risk of microaspiration and enteral feedingvia a nasogastric tube increases the risk of aspiration of gastric
contents. It follows that attempts to prevent VAP would focus
on measures to reduce biofilm formation and microaspiration.
VAP prevention
A care bundle refers to a group of evidence-based interventions
related to a particular condition which when applied together
significantly improves patient outcome. In 2007, the Department
of Health launched ‘Saving Lives; reducing infection, delivering
clean and safe care’, a campaign to prevent and control hos-
pital-acquired infection. This included ‘High Impact Intervention
No 5—Care bundle for ventilated patients’, the aim of which was
to reduce VAP. The original document consisted of daily sedation
holds, bed head elevation, gastric ulcer prophylaxis, and oral
care. It was updated in 2010 to include oral hygiene with ad-
equate strength anti-septics, subglottic aspiration, and TT cuff
pressure monitoring in addition to the initial four care interven-
tions. A before and after study based in a large Scottish ICU
studied the effectiveness of the original four high impact inter-
ventions (HII). They were able to demonstrate over 95% adher-
ence with the bed end elevation and chlorhexidine elements
and 70% compliance with the wake and wean elements (overall
bundle compliance 70%). There was a significant reduction in
their VAP rates (from 32 cases per 1000 ventilator days pre-inter-
vention to 12 cases post-intervention), methicillin-resistant
Staphylococcus aureus rates, and antibiotic use. However, they
were unable to demonstrate a reduction in the duration of mech-
anical ventilation and overall ICU admission duration.9 A similar
study based in Spain used intra-cuff pressure control in addition
to the other four methods. Although overall compliance was
<30%, they were able to demonstrate reduction in VAP rates,
ICU length of stay (LOS), and duration of mechanical ventila-
tion.10 However, a systematic literature review of four studies
concluded that the lack of methodological rigor precluded any
conclusive statements regarding the bundles’ effectiveness or
VAP prevention
TT modification
As it is the TT that provides the continuous path between the oral
cavity and the distal airways, VAP prevention strategies have
focused on TT cuff design to prevent microaspiration.
VAP prevention
Cuff pressure control
An inflating cuff pressure <20 cm H2O favours increased passage
of secretions between the cuff and the wall of the trachea, while
>30 cm H2O may cause tracheal mucosal damage. Despite routine
cuff pressure controls, variations in TT cuff pressure frequently
occur, exposing patients to increased risk of VAP. Several devices
have been developed to constantly monitor and adjust the
TT cuff inflation pressure. Randomized controlled trials have
shown a reduced rate of VAP in the treatment arm of a study
testing the Nosten device (Nosten; Leved, St Maur, France)
Subglottic secretion drainage
Subglottic secretion drainage systems usually consist of an
accessory aspiration conduit opening above the TT cuff and a
vacuum source. Secretions may be continuously or intermittent-
ly removed from the subglottic space. A meta-analysis of 13 ran-
domized controlled trials showed that subglottic secretion
drainage was effective at reducing VAP rates, also reducing thetime to onset of first VAP, reduced duration of mechanical venti-
lation, and reduced ICU LOS.13
T cuff design
Most common TT cuffs have a high volume–low pressure cuff
made of poly vinyl chloride. The surface of a traditional TT cuff
folds when inflated in the trachea, creating potential channels
through which secretions can drain. A tapered cuff shape made
of ultra thin polyurethane seems to offer the most protection
against secretion channelling leading to VAP.1
TT coating
Bacterial colonization and biofilm formation on the inner surface
of the TT can be prevented by coating it with a thin layer of anti-
microbial agents. Among many agents, silver appears to have
been the most widely studied. NASCENT was a multicentre
study that recruited more than 2000 patients to be randomized
to either a silver-coated TT or a standard TT. They reported a sig-
nificant reduction in VAP rates in the treatment arm and delayed
time to onset of VAP. However, they were unable to show a reduc-
tion in ICU LOS or duration of ventilation.15 Other agents used for
coating include chlorhexidine and titanium dioxide.
Nebulized gentamicin
This has been investigated as a means of prevention of biofilm
formation. Compared with systemic cephalosporins, nebulized
gentamicin attained a higher concentration within the TT and
there was a lower incidence of biofilm formation. Interestingly,
none of these biofilms was from organisms that commonly
cause VAP. However, more work needs to be done before this
method can be recommended.16
Kinetic therapy
Mucociliary clearance is inhibited by immobility. Mechanical ro-
tation of patients with 40° turns achieves more significant clear-
ance of secretions than current standard therapy of 2 hourly
turns. It has been shown to lower the incidence of VAP, but
have no effect on duration of ventilation, LOS, or mortality. How-
ever, kinetic therapy requires specialist equipment and has been
associated with significant complications such as intolerance to
rotation, unplanned extubations, loss of vascular access, and
arrhythmias.
Care of airway equipment
Studies have shown that TT colonization and biofilm formation
begins within 24 h of intubation. Strict attention to hand hygiene
when handling the TT, closed-circuit suction systems, use of heat
and moisture exchangers, and limiting ventilator tube changes to
whenever they are soiled, all contribute towards reducing biofilm
formation.
Feeding
Although the early establishment of enteral feeding is of benefit
to critical care patients, reflux and aspiration of gastric contents
is the main cause of VAP. It has been suggested that post-pyloric
feeding may reduce the incidence of VAP. Several studies so far
have shown a non-significant trend towards a reduction in VAP,
but more conclusive evidence is needed before a definite recom-
mendation is made
