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Strategies
to Prevent Ventilator-Associated Pneumonia
Pneumonia is the second most
common nosocomial infection in the United States,
accounting for 13% to 18% of all nosocomial infections.
Fatality rates associated with nosocomial pneumonia
range from 20% to 50%.
Critically ill patients who require mechanical
ventilation are especially vulnerable to development of
ventilator-associated pneumonia (VAP); incidence is
estimated to range from 10% to 25%.
Negative outcomes associated with VAP include increased
mortality and morbidity and prolonged hospital stay.
In French studies, results showed that critically ill
patients in whom VAP developed were twice as likely to
die as were those who did not acquire pneumonia,
and the risk of pneumonia increased from 6.5% in those
ventilated 10 days, to 28% in those ventilated 30 days.
Nosocomial pneumonia also has an economic impact. Using
figures compiled from several studies, Wiblin estimated
that 250,000 annual cases of nosocomial pneumonia in the
United States account for 1.75 million excess hospital
days and $1.5 billion in extra costs.
In-depth articles in the
literature include a comprehensive discussion of the
1994 Centers for Disease Control (CDC) Guidelines for
Preventing Nosocomial Pneumonia
and two similar articles by Craven and Steger.
In the current article, the pathogenesis, risk factors,
and diagnosis of VAP are described, with a focus on
aspiration as a main cause. (Although important,
management of the mechanical ventilator and respiratory
equipment is not discussed here.) Strategies for the
nursing clinician and advanced practice nurse to assist
in diagnosis and prevention of VAP are discussed. A case
study is used to illustrate key concepts.
Standardized Reporting
An accurate accounting of
the incidence of VAP is difficult to obtain because
criteria used to diagnose pneumonia vary from study to
study.
Diagnostic
criteria include such clinical indicators as fever,
purulent tracheal secretions, leukocytosis, and changes
on chest radiograph. In recent studies, more
sophisticated techniques (e.g., bronchoalveolar lavage)
have been used. Another limitation in evaluating
incidence of VAP is that many of the studies have been
conducted in Europe, and findings may not correlate with
data from the United States, because practice and
standards differ.
To facilitate
standardization and interpretation of data, infection
rates for VAP are reported per 1,000 ventilator days.
In the United States, data regarding nosocomial
pneumonia are collected by the National Nosocomial
Infections Surveillance (NNIS) System through the CDC.
The NNIS collects data from 231 hospitals that report
infection rates using standard CDC criteria for
determination of infection. According to 1996 NNIS
statistics based on more than 13,000 cases during the
past decade, the mean rate of VAP ranges from 6.4 to
20.9 cases per 1,000 ventilator days (Table 1). Lowest
rates are reported in patients in pediatric intensive
care units (ICUs), whereas highest rates are reported in
the neurosurgical and burn populations.
A rate of 12.3
cases per 1,000 ventilator days is noted when all data
in Table 1 are combined.
|
Table 1.
Rate of Ventilator-Associated Pneumonia per 1000
Ventilator Days (NNIS Data) |
|
Type of Intensive Care Unit
|
No.
|
Mean
|
Median
|
|
Pediatric |
58
|
5.9
|
5.0
|
|
Respiratory |
5
|
6.4
|
NR
|
|
Medical |
89
|
9.4
|
8.5
|
|
Coronary |
81
|
9.9
|
8.1
|
|
Surgical |
143
|
14.9
|
13.2
|
|
Medical-surgical |
171
|
12.5
|
11.5
|
|
Trauma |
15
|
16.9
|
NR
|
|
Neurosurgical |
30
|
20.2
|
16.5
|
|
Burn |
14
|
20.9
|
NR
|
|
Total*
*computed by the authors
NR =
not reported |
606
|
12.3
|
 |
|
|
|
|
|
Pathogens
The pathogens responsible
for nosocomial infections may originate in the patient’s
endogenous flora or in the hospital environmentother
patients, staff members, and invasive devices.
Most VAP results from aspiration of bacteria colonizing
the oropharynx or gastrointestinal (GI) tract.
According to NNIS data (Table 2), the following
pathogens account for more than half of the cases of
nosocomial pneumonia:
Staphylococcus aureus,
Pseudomonas aeruginosa, Enterobacter sppand
Klebsiella pneumoniae.
Gram-negative bacteria are
implicated in more than 60% of all cases of nosocomial
infections.
Infections with P.
aeruginosa and Acinetobacter
spp have been associated with higher mortality rates
from VAP.
More than one organism is responsible for VAP in at
least 25% of those infected.
Pathogens differ according
to the onset of VAP. Onset of infection can be divided
into early and late phases. Early-onset VAP is described
as that which occurs 1 to 4 days after admission.
Organisms responsible for early-onset VAP are usually of
oropharyngeal species and include
Streptococcus pneumoniae, S.
aureusand
Haemophilus influenzae.
Late-onset VAP occurs more than 4 days after admission
and is usually associated with gram-negative bacteria.
Causative agents include
P. aeruginosa, Acinetobacter
spp, and Enterobacter spp.
The NNIS data reflect all causative agents for VAP but
do not describe the time frame in which pneumonia
develops.
|
Table 2.
Causative Pathogens for Nosocomial Pneumonia* (NNIS) |
|
Causative Organism
|
Occurrence (%)
|
|
Staphylococcus aureus |
19
|
|
Pseudomonal aeruginosa |
17
|
|
Enterobacter spp. |
11
|
|
Klebsiella pneumoniae |
8
|
|
Haemophilus influenzae |
5
|
|
Candida albicans |
5
|
|
Escherichia coli |
4
|
|
Acinetobacter spp. |
4
|
|
Other nonenterobacteriaceae aerobes |
4
|
|
Serratia marcescens |
3
|
|
Coagulase-negative
staphylococci |
2
|
|
Enterococcus |
2
|
|
Proteus mirabilis |
2
|
|
Citrobacter spp. |
1
|
|
Other
Streptococcus spp. |
1
|
|
Group B
Streptococcus |
1
|
|
Other
Candida |
1
|
|
Other fungi |
1
|
|
Other
Klebsiella spp. |
1
|
|
Other enterobacteriaceae aerobes |
1
|
|
Viruses |
1
|
|
All
others (pathogens with less than 1% isolates) |
6
|
|
Total
*from the National Nosocomial Infections
Surveillance Report 1996 |
100
|
Risk Factors
Risk factors and host
defenses altered by placements of artificial airways
contribute to the development of pneumonia once
colonization occurs. In a recent study by Bonten et al.,
risk factors for VAP were evaluated in 141 patients.
Significant risk factors for VAP were identified:
duration of mechanical ventilation, oropharyngeal
colonization, and infection on admission to the
hospital.
Host,
Device, and Personnel-Related Risks
Host-related factors include
age more than 65 years; underlying illness including
chronic obstructive pulmonary disease; immunosuppression;
depressed consciousness; and thoracic or abdominal
surgery. Device-related factors include endotracheal
intubation, mechanical ventilation, nasogastric tube
placement, and enteral feedings. Personnel and
procedure-related factors include cross-contamination of
patients by staff and administration of antibiotics.
Altered Host Defenses Related to Intubation
In critically ill patients,
several factors associated with intubation and
mechanical ventilation alter normal defenses against
infection. These factors increase the likelihood of VAP.
Lack of
Anatomic Barriers
Once a patient is intubated,
bacteria have direct access to the lower airways,
because the endotracheal tube bypasses normal filtration
mechanisms and the barrier function of the epiglottis.
In addition, the endotracheal tube provides a direct
route for inoculation of the lungs with such bacteria as
P. aeruginosa.Inoculation
is caused by inadequate hand washing, using the same
gloves from patient to patient, and contaminated
respiratory devices, including in-line nebulizers,
spirometers, oxygen sensors, bag-valve mask devices, and
suction catheters. P. aeruginosa
adapts and adheres to the respiratory tract better than
does other gram-negative bacteria. The
P. aeruginosa
pathogen also produces exoproducts that affect cellular
function and structure in the tracheobronchial tree and
impair host defenses.
Impaired
Cough
Intubation
interferes with natural host mechanisms by reducing the
cough effort, interfering with mucociliary clearance,
and injuring the epithelial layer, thereby exposing the
basement membrane. These last two factors injury to the
epitheium and basement membrane appear to play a key role
in facilitating bacterial adherence and colonization.
Alteration of Mucus and Mucociliary Clearance
Mucus is normally
produced to trap bacteria, which is then removed by
mucociliary clearance. Intubation may result in
increased production of mucus and stagnation of mucus in
the respiratory tract. These factors, combined with
impaired mucociliary clearance, increase the risk of
VAP.
Pathophysiology
The respiratory tract above
the vocal cords is colonized with "normal" aerobic and
anaerobic bacterial flora. The sterility of the lower
respiratory tract is usually maintained by a tightly
controlled, coordinated host defense system.Colonization
describes the presence of bacteria without evidence of
host response and with no adverse effects.
It is proposed that colonization is related to bacterial
adherence. Bacteria adhere to epithelial surfaces
through substances called adhesins. For bacterial
adherence to result in colonization, the organism must
have an adhesin molecule for the epithelial surface, the
site must have an appropriate receptor, and prolonged
epithelial exposure must occur.
Many factors influence bacterial adherence.
The lung is colonized by
nosocomial pathogens in many ways: microaspiration of
oropharyngeal secretions, aspiration of gastric
contents, direct inoculation into the airways of
intubated patients, inhalation of infected aerosols,
hematogenous spread of infection from a distant site,
and potentially, translocation of bacteria from the GI
tract.
Most VAP is associated with the aspiration of bacteria
from the oropharynx and GI tract.
Microaspiration of Oropharyngeal Secretions
Oropharyngeal secretions
commonly become colonized with pathogens, especially
gram-negative bacteria. Gram-negative bacteria are not
part of the normal flora of the oropharyngeal tract, and
their presence in oropharyngeal secretions is a
predictor for the development of VAP.
Several factors, including those associated with the
endotracheal tube increase the likelihood of
microaspiration.
Endotracheal Tube Cuff
Mechanical ventilation
requires intubation with a cuffed endotracheal tube
(oral or nasal) or tracheostomy tube. The cuff of the
tube is inflated to facilitate ventilation of the lungs.
Despite adequate inflation of the cuff, microaspiration
often occurs. Bacteria from the oropharynx and GI tract
can migrate below the endotracheal tube cuff. Secretions
that have pooled above and around the cuff leak and
enter the trachea.
Endotracheal Tube As Reservoir
The endotracheal tube
serves as a reservoir for bacteria. It serves as a safe
haven from antibiotics and host defense mechanisms, in
that they have no access to destroy bacteria. Bacteria
that colonize endotracheal tubes form a bacterial
biofilm within the tube
that may be dislodged by suctioning, coughing, or
movement of the tube, increasing the risk of bacterial
contamination of the lower respiratory tract.
Oral
Versus Nasal Tube Placement
Although not directly
related to aspiration, nasal placement of endotracheal
and GI tubes increases the risk for sinusitis. The sinus
provides a reservoir from which organisms seed the
tracheobronchial tree.
Diagnosis of sinusitis is difficult to make. Computed
tomographic scan of the sinuses and trans-nasal puncture
to obtain a culture are two diagnostic methods used.
Bacteria causing sinusitis
can colonize the upper airway, increasing the risk of
VAP. Infectious sinusitis occurs in 20% to 30% of
patients who have been intubated at least a week.
Research has
linked sinusitis to nasal placement of tubes and
duration of tube placement. Rouby et al. noted that
sinusitis occurred in 73% of mechanically ventilated
patients who were intubated through the nose as opposed
to a 34% incidence in those who were orally intubated.
In patients who had sinusitis, 34% had evidence of
sinusitis within 12 hours of intubation and nasogastric
tube placement, and 80% had signs within a week of tube
placement. Incidence of sinusitis and VAP were
significantly reduced when tubes were placed orally and
discontinued as soon as possible.
Decreased
Consciousness
Patients with a
decreased level of consciousness from disease, injury,
or medications that depress the central nervous system
lose such protective mechanisms as the cough and gag
reflexes. The inability to cough or gag when foreign
substances are aspirated increases the risk of bacterial
colonization and VAP.
Aspiration of Gastric Contents
An increased incidence of
VAP has been associated with sub clinical aspiration of
gastric contents,
although results in one study led to the conclusion that
gastric colonization was not a risk factor associated
with the development of VAP.
Several factors are related to aspiration of gastric
contents and colonization of the respiratory tract by
pathogens from the GI tract. Most critically ill
patients have a nasogastric or naso-enteric tube inserted
for gastric decompression or nutritional support. Such
tubes increase the risk of aspiration through such
mechanisms as reflux and translocation of bacteria.
Medications and enteral feedings can alter the acidity
of gastric juices, increasing the likelihood of
bacterial growth. Improper positioning during feeding
may also increase the risk for aspiration of GI
contents.
Reflux
When nasogastric or
nasoenteric tubes are placed, the gastroesophageal
sphincter is violated, enhancing the potential for
gastrointestinal reflux. Once reflux occurs, the upper
airway is exposed to an increased number of bacteria.
Gastrointestinal tubes may also provide a mechanism for
bacteria to migrate, referred to as translocation, up to
the oropharynx and colonize the airway.
Stress
Ulcer Prophylaxis
The use of antacids and H2 receptor-antagonists have
been identified as contributing factors for the
development of VAP.
These drugs are prescribed in critically ill patients
for stress ulcer prophylaxis. They increase the pH of
gastric secretions, which affects the normal flora of
the GI tract. Pathogens proliferate in gastric
secretions, increasing the likelihood of VAP, should
aspiration of gastric contents occur. Duodenal reflux
and a gastric pH higher than 3.5 have been associated
with increased bacterial colonization of the lower
respiratory tract.
In many studies during the
past few years, the incidence of VAP has been recorded
with administration of antacids, H2
receptor-antagonists, or sucralfate to prevent stress
ulcers. There is controversy about which therapy is best
in critically ill patients.
Kappstein et al. compared
the incidence of VAP in 104 mechanically ventilated
patients who were treated with cimetidine or sucralfate.
The incidence of VAP was 45.5% in the cimetidine group
and 26.5% in the sucralfate group. Mean gastric pH
values were significantly lower in the group that
received sucralfate, which decreases the likelihood of
bacterial growth.
Prod’hom et al. conducted a
study of 244 patients who were randomized into one of
three groups to receive antacids, ranitidine, or
sucralfate. The incidence of early onset pneumonia was
not statistically different among groups. The
investigators observed 213 patients for more than 4 days
for development of late-onset VAP. The incidence of
pneumonia in this cohort was 5% in the sucralfate group,
16% in the group receiving antacids, and 21% in the
ranitidine group. The group receiving sucralfate had a
decrease in the median gastric pH and a decrease in
gastric colonization.
Results of this study support the theory that early
onset VAP is caused by oropharyngeal colonization,
whereas late-onset pneumonia is related to gastric
colonization.
In results of a similar
study of trauma patients, no difference was noted in the
incidence of VAP in the first 4 days of stress ulcer
prophylaxis. A trend was noted toward a declining rate
of VAP after the fourth day of treatment in the group
receiving sucralfate.
Cook and Reeve conducted a
meta-analysis to evaluate outcomes of drugs used for
stress ulcer prevention. Their results showed that use
of sucralfate resulted in a lower incidence of VAP.
Enteral Feedings
Another
risk factor for VAP is enteral feedings. In results of a
recent study, it was noted that 80% of all patients were
colonized after 7 days of enteral feeding.
Feeding
patients enterally increases the intragastric volume and
thereby increases the risk of aspiration of stomach
contents. Contamination of the tube-fed material has
also been identified as a potential source of
colonization and VAP. Feedings may also alter gastric
pH, increasing bacterial growth.
Supine Positioning
Supine positioning has been associated with an increased
risk of aspiration and VAP.
The duration of supine positioning has also been
identified as a risk factor.
If regurgitation occurs secondary to gastric distension,
aspiration is more likely in patients who are supine.
Direct
Inoculation of the Airway
Organisms can be introduced
directly into the endotracheal tube of patients. This is
a common route for P. aeruginosa. Health care workers
are usually responsible for the direct inoculation of
the patient, usually from inadequate hand washing or
failure to change contaminated gloves when treating more
than one patient.
Diagnosis
Although accurate diagnosis
of VAP is difficult, it is essential to guide effective
treatment. Many patients in whom VAP is suspected are
found not to have pneumonia when specimens obtained in
invasive bronchoscopic testing are analyzed. Yet,
antimicrobial therapy is often initiated in these
patients. Antibiotic treatment for patients who do not
have VAP exposes them to potential toxicity, delays
determination of the true cause of pulmonary
infiltrates, increases cost, and favors the emergence of
resistant microorganisms.
The best diagnostic methods
demonstrate sensitivity and specificity. Sensitivity is
the probability that a disease (VAP in this article)
will be correctly diagnosed in a person, whereas
specificity is the probability that the person who does
not have VAP will be identified.
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Clinical Diagnostic Criteria
Clinical diagnosis for VAP
is based on the following CDC criteria: new or
progressing pulmonary infiltrates detectable on chest
radiograph, fever higher than 38 degrees Centigrade,
leukocytosis (more than 10,000 wbc/mm3),
and purulent tracheal secretions.
These criteria are often inadequate in confirming a
diagnosis of VAP, because infiltrates can occur from
atelectasis and other pulmonary conditions and because
in most critically ill patients, fever and leukocytosis
develop.
Cultures of endotracheal
aspirate (sputum for culture and sensitivity) are
routinely performed in many institutions when VAP is
suspected. However, results of sputum cultures may yield
false-positive results because of colonization of the
upper airway, or false-negative results because
specimens are not obtained from the suspected area of
lung infection.
In a recent study, there was only 40% agreement between
results of analysis of sputum cultures obtained by
suctioning and results in those specimens obtained in
other more invasive methods (described later); and
false-negative results were obtained in analysis of 8 of
11 specimens.
Bronchoscopic Methods for Diagnosis
To improve accuracy of
diagnosis, invasive diagnostic testing using
bronchoscopic methods is recommended. Two invasive
methods are protected specimen brush (PSB) and
bronchoalveolar lavage (BAL). Quantitative cultures are
done with both PSB and BAL, and results help to
establish an accurate diagnosis and to guide
prescription of optimal antimicrobial treatment.
Sensitivity of both tests may decrease if the patient is
receiving antibiotics or is immunosuppressed. Although
values that are considered positive results are noted
below for the reader, varying values are cited in the
literature.
Protected
Specimen Brush
In PSB, a catheter is inserted through the bronchoscope
into the area of lung in which pneumonia is suspected.
Using a microbiology specimen brush, a sample is
obtained by expressing and retracting the inner cannula
and brush. The brush tip is placed in a small amount (1
mL) of sterile, preservative-free saline and is
processed. Test results are considered positive if
organisms grow at 103 colony-forming units (CFU)/mL or
more. Disadvantages of PSB are that the specimen must be
taken from the affected portion of the lung, the sample
is not adequate for gram staining, and culture results
are delayed for 24 to 48 hours.
Bronchoalveolar Lavage
Bronchoalveolar lavage is similar to PSB, except that a
larger amount of sterile, preservative-free saline is
instilled in the lung area if pneumonia is suspected,
and secretions are aspirated until an adequate specimen
is obtained. Bronchoalveolar lavage obtains cells and
secretions lining the lower respiratory tract, and a
gram stain can be performed in the specimen. Test
results are considered positive if organisms grow at 104
CFU/mL or more.
Nonbronchoscopic Methods
Nonbronchoscopic techniques,
including "blind" PSB or BAL, are used to aid in
accurate diagnosis of VAP. Techniques used in
nonbronchoscopic PSB and BAL are similar to those used
in bronchoscopic procedures; however, the specimen is
obtained through the endotracheal tube, using either a
specimen brush or a specially designed suction catheter
(BAL Cath, Ballard Medical Products, Draper, UT). In a
recent study of 15 trauma patients, culture results
using nonbronchoscopic methods ("blind" PSB and BAL)
were similar to those obtained by bronchoscope, took
less time to obtain, and the procedure was more
cost-effective to perform.28
Kollef et al. obtained similar results using mini-BAL
techniques.
Wiblin reviewed more than a
dozen studies in which conventional endotracheal
aspirated, PSB, and BAL techniques were compared. He
determined that BAL had the highest sensitivity (80% to
100%) and specificity (75% to 100%) of the methods.
Bronchoalveolar lavage provides more accurate results
because the specimen is taken from a larger area of the
bronchial tree and because pathogens are more likely to
be detected.
Not every clinician
advocates extensive and costly testing to diagnosis
pneumonia. Helling et al. contend that although clinical
indicators overestimate the incidence of pneumonia by as
much as 50%, the outcomes of the patients were similar.
They recommend treatment with antibiotics in patients
who have been diagnosed solely on clinical parameters.
Recommendations
for Nursing Practice
Based on a review of the
literature, several recommendations for preventing VAP
are presented. Some of these suggestions have been
promoted by the CDC; others are based on results in
studies that have been published since the 1994 CDC
guidelines were published. Several have been generated
by the current authors based on review of the literature
and warrant further evaluation.
Assist
in Establishing an Accurate Diagnosis
Most researchers and the CDC
recommend that treatment of VAP be based on clinical
indicators and such confirmatory methods as PSB and BAL.
Bronchoscopic BAL appears to have the most sensitivity
and specificity of the methods currently used in
diagnosis of VAP.
Routine culture to determine the sensitivity of
endotracheal aspirate is not an accurate method for the
diagnosis of VAP and may be unnecessary. Nurses and
respiratory therapists should be informed of this
finding, because they frequently obtain sputum cultures
when purulent secretions are noted.
Because results in recent
studies have indicated that nonbronchoscopic PSB and BAL
yield findings similar to those of bronchoscopic
methods, use of nonbronchoscopic BAL techniques for
obtaining specimens is recommended for performing
ongoing evaluations.
Selected staff can be trained in the proper procedure
for collecting specimens. The advanced practice nurse
(APN) can work with the multidisciplinary team to assist
in developing diagnostic protocols, training staff in
proper techniques, evaluating cost-effectiveness, and
comparing accuracy of results of bronchoscopic and
nonbronchoscopic techniques.
Reduce
Colonization
The first step in preventing
VAP is to prevent colonization by pathogens of the
oropharynx and GI tract. Basic nursing care principles
are essential. It is important that these basics not be
omitted when delivering high-tech care in the ICU.
Hand
Washing and Use of Gloves
Meticulous hand washing is the first step in reducing
colonization. Gloves are needed when suctioning patients
orally or through the endotracheal tube. Gloves are also
recommended when closed-suction devices are used. During
closed suctioning, the hands may come into contact with
the patient’s mouth and may serve as a source for
introducing pathogens to the patient’s oropharynx.
Gloves must be changed whenever contaminated and between
treating each patient. Although these recommendations
seem simplistic, many times staff are observed leaving a
patient’s room with gloves on, and proceed to enter data
on the patient’s record, answer the phone, and perform
other duties.
Oral
Hygiene
Although
considered a standard nursing intervention, oral hygiene
is often neglected when caring for intubated patients.
Many times, it is performed by quickly swabbing the
mouth. Oral care involves brushing the patient’s teeth,
use of solutions and mouthwash to cleanse the mouth, and
thorough suctioning of oral secretions. Systematic oral
assessment is recommended in intubated patients.
Studies evaluating effectiveness of various methods of
oral care are needed.
Nasal
Hygiene
Meticulous nasal care and cleansing of the nasopharynx
may reduce bacterial colonization. As in oral care,
nasal care is often neglected as a part of routine
hygiene. Most patients have an nasogastric or
nasoenteric tube in place, and the endotracheal tube may
be placed nasally. The tubes remain taped for prolonged
periods, and secretions accumulate and crust in the
nares. Protocols for routinely cleansing the nose and
suctioning nasopharyngeal secretions should be
implemented and evaluated. The APN can collaborate with
experienced staff nurses to develop protocols for oral
and nasal care.
Turning
and Positioning
Stagnant mucus in the lower airways is a medium for
bacterial growth, should pathogens reach the lower
airways. Routine turning and positioning assists in
mobilization of secretions. Use of therapeutic beds that
provide vibration or rotation to prevent VAP should be
studied.
Studies of rotational therapy have produced variable
results, because of small sample sizes, no
differentiation between VAP and community-acquired
pneumonia, and lack of consistent diagnostic criteria
for pneumonia.
The use of prone positioning
for critically ill patients is currently advocated as a
method for improving oxygenation in patients with adult
respiratory distress syndrome. Its use in
prevention of pneumonia should also be evaluated.
Strategies for preventing aspiration of feedings are
necessary if prone positioning is used.
Endotracheal Suctioning
The current standard of care is to suction patients only
when need is determined by auscultation of adventitious
lung sounds or other assessments. The rationale for this
standard is to reduce trauma to the airways. However,
some patients have minimal secretions and may not have
to be suctioned for several hours. Because stagnant
mucus and lack of a cough reflex are risk factors for
the development of VAP, suctioning and interventions to
facilitate effective coughing may be needed
periodically. This issue is presented for discussion and
critical analysis by clinicians and APNs, and evaluation
is warranted.
Maintaining aseptic
technique when endotracheal suctioning is needed to
reduce contamination of the oropharyngeal cavity. When
closed-suction catheters are used, it is important to
rinse the secretions according to manufacturer’s
recommendations to remove mucus from the suction
catheter and to reduce the likelihood of bacterial
growth. Staff are frequently
observed using closed-suction devices and not rinsing
the system when finished.
Closed-suction catheters
have not been associated with an increased risk of VAP. The
frequency of changing closed-suction devices and the
need for rinsing should be evaluated further. Current
practice is to change the devices every 24 hours,
although some institutions are extending usage.
Nasal
Tubes
Oral tubes
pose the least risk for development of sinusitis. The
earlier tubes can be removed, the less potential there
is for bacterial invasion and infection.
Stress
Ulcer Prophylaxis
Each patient should be individually evaluated for the
need for medications to prevent stress ulcers. If
prophylaxis is deemed necessary, agents (e.g.,
sucralfate) that do not alter the gastric pH are
recommended.
However, it may not be feasible to request that
sucralfate be ordered, because it must pass through the
stomach for therapeutic effectiveness, and many
critically ill patients have intestinal tubes. The APN
must work with the multidisciplinary team to develop
assessment criteria for use of stress prophylaxis.
Selective
Digestive Decontamination
Selective digestive decontamination (SDD) was proposed
and evaluated in Europe, in mechanically ventilated
patients, as a strategy to prevent colonization and to
lower respiratory tract infection, without disturbing
the anaerobic flora. In studies, SDD regimens vary,
depending on the design of the study. A combination of
locally administered nonabsorbable antibiotic agents is
applied as a paste to the oropharynx and is given orally
or by nasogastric tube four times a day. In some trials
an intravenous antimicrobial agent is also administered.
Results in two recent large
studies have shown no benefit of SDD. Gastinne et al.
recorded a decrease in the rate of gram-negative
pneumonia in 445 patients who received SDD or placebo,
but no decrease in the overall incidence of VAP. They
noted 2.2-fold higher cost of antibiotics for SDD
subjects and no improvement in survival rate.
Hammond et al. found no differences in incidence of VAP
in the experimental or control groups.
In that selective digestive decontamination has not been
conclusively shown to reduce the incidence of VAP or to
improve survival rates, it is not recommended for
routine use.
Reduce
Aspiration of Oropharyngeal Secretions
Because aspiration of
oropharyngeal secretions is a primary route for
acquiring VAP, strategies to reduce aspiration of
secretions are recommended. Routine and innovative
recommendations are proposed.
Early
Extubation
Because the likelihood of pneumonia increases the longer
patients are ventilated, separation from mechanical
ventilation as soon as possible must be a priority. The
use of separation indexes to evaluate readiness to
breathe independently along with an aggressive team
approach to separation is encouraged.
Accidental Extubation
Reintubation increases the risk for VAP. Therefore,
strategies to prevent unplanned extubation are
warranted.
Endotracheal Cuff Pressure
The incidence of VAP increases when the endotracheal
cuff pressure is less than 20 cm water pressure.
It is important to check cuff pressures routinely and to
maintain at least 20 cm of pressure. Assessments must be
recorded in the medical record.
Repositioning Endotracheal Tubes
Oral endotracheal tubes are repositioned and retaped
according to hospital protocol, usually once a day. The
rationale for repositioning tubes is to prevent
breakdown of the oral mucosa and mouth. There is no
guidance in reported research regarding frequency of
repositioning tubes. Because pooled secretions above the
endotracheal cuff are associated with VAP, it is
important that thorough oral suctioning be performed
before repositioning tubes. Optimal frequency of
repositioning tubes should be established.
Aspiration of Subglottic Secretions
Studies have been conducted in Europe evaluating a
special dual-lumen endotracheal tube that has a port
through which subglottic secretions are continually
aspirated. Results in a randomized trial of this new
tube versus conventional endotracheal tubes showed a
significant decrease in VAP in the patients with
continuous subglottic aspiration and a delay in onset of
VAP.
Failure of the continuous aspiration device was cited as
a risk factor for VAP.
This is a fairly new treatment that appears to be
beneficial, and ongoing evaluation is recommended.
Clinical trials are underway in the United States.
Because continuous
aspiration has yielded positive results but is not yet
available, alternative methods for aspiration may be
tried for example, thoroughly suctioning the oropharynx
of patients every 1 to 2 hours in an attempt to decrease
the amount of pooled secretions around the endotracheal
cuff.
Another option is to use
readily available supplies to aspirate secretions
continuously. When Sengstaken-Blakemore tubes are
inserted into patients to treat bleeding esophageal
varices, a second tube is routinely placed to aspirate
secretions that accumulate above the esophageal balloon
continuously.
A similar procedure could be evaluated as part of
endotracheal tube management. This recommendation has
not been made previously in the literature, nor has it
been tested; however, a nasogastric tube could be
inserted orally until it is located above the
endotracheal tube cuff and connected to continuous low
suction. Disadvantages may include difficulty in
anchoring the tube, patient discomfort, and trauma to
the oropharynx if suction level is set too high.
Choice of
Endotracheal Tubes
In all of the studies reviewed for this article,
conventional, cuffed endotracheal tubes were used to
provide mechanical ventilation. It is not known whether
foam cuff tubes increase or decrease the likelihood of
VAP. Theoretically, these tubes provide a better seal in
the trachea and could reduce microaspiration.
Reduce
Aspiration of Gastric Secretions
Strategies to reduce
aspiration of gastric secretions are also important in
reducing VAP. Many researchers have investigated
strategies for reducing aspiration, and findings of
studies often conflict.
Need For
a Nasogastric Tube
Any patient with a nasoenteric tube should be
reevaluated frequently and have the tube removed as soon
as possible. If the patient needs long-term enteral
feedings, early placement of a jejunostomy or
gastrostomy feeding tube is recommended.
Head
Elevation
The
semirecumbent position, with the head of bed elevated to
30 to 45 has been effective in reducing the risk of
aspiration. Elevating the head of the bed is based on
the notion that gravity will reduce the possibility of
regurgitation in an overly distended stomach.
It is recommended that supine positioning be avoided
unless clinically necessary. Patients should be supine
for the shortest time possible.
Studies are needed to
determine whether tube feedings should be turned off for
placing patients supine for procedures, for turning, and
for other nursing care activities. Such studies are
difficult to design and implement because of the
frequency of patient repositioning.
Verification of Tube Placement
Once postpyloric placement of enteral feeding tubes has
been established, the tube should be marked and
insertion depth documented in the patient’s medical
record. This will assist in
ongoing assessment of tube placement. Protocols for
assessing nasogastric tube and nasoenteric tube
placement can be developed by the APN.
Gastric
Residuals
Patients receiving tube feeding must be closely
monitored for aspiration. Checking residual volumes is
one method of assessment.
High residual
gastric volumes may occur when gastric emptying is
impaired, increasing the likelihood of regurgitation and
aspiration. No standard for checking residuals has been
established. Based on review of the literature and on
clinical experience, residuals should be checked every 2
hours when feedings are initiated. Once tube feedings
are progressing without difficulty, residuals can be
checked every 4 to 6 hours. Although it is believed that
residual volumes are small when intestinal tubes are
used for feeding, assessment is important to indicate
whether the tube has migrated back into the stomach.
Continuous Versus Intermittent Tube Feeding
Although it is hypothesized that the method of tube
feeding may affect gastric acidity, gastric colonization
was compared in patients receiving continuous versus
intermittent tube feeding. The mean gastric pH was below
3.5 in both groups, and no differences in incidence of
gastric and respiratory colonization were noted between
methods. However, intermittent bolus feedings were not
well tolerated.
These results support the current standard of continuous
enteral feeding.
Gastric
Versus Intestinal Feeding
Where to place feeding tubesin the stomach or the small
intestineis another issue related to aspiration.
Clinicians tend to favor intestinal placement of tubes
in an attempt to decrease the risk of aspiration. In addition, it
is believed that early enteral feeding into the small
intestine is better tolerated by critically ill
patients. However, another researcher found that
aspiration was associated with both feeding methods.
Although further investigation is needed, rationale for
feeding into the small intestine supports its use to
reduce the risk of VAP. The CDC considers this issue to
be unresolved.
Evaluating Swallowing
Oral feeding is initiated in patients with tracheostomies and in some patients who are nasally
intubated. It is important to avoid oral feedings in
patients with artificial airways until a dysphagia
evaluation and a rehabilitation swallow are completed.
Subclinical aspiration is common in this group, and
these studies help to determine the risk of aspiration.
Other
Unresolved Issues
Some issues related to enteral feeding are still
unresolved. What size tubes should be used in patients
receiving enteral nutritionlarge- or small-bore? Do
jejunal tubes decrease the risk of aspiration compared
with the risk in tubes placed in the stomach or in the
duodenum? Should tube feedings be routinely acidified to
decrease the risk of colonization?
Further study on all of these issues is needed.
Collaborative Protocols for Preventing VAP
The APN plays a key role in
meeting with a multidisciplinary team to develop
protocols for preventing VAP in critically ill patients.
Collaboration with respiratory care departments,
pulmonologists, intensivists, and infectious disease
physicians is essential. Development of monitoring
tools, clinical protocols, and evaluation tools for
quality assessment are important activities for the APN
to pursue to reduce the incidence of VAP. The majority of
studies reviewed for this article were conducted by
physicians, yet the recommendations proposed are
targeted to nurses. Development of clinical research
protocols that evaluate nursing interventions to prevent
VAP are needed.
Case Study
The multiple risk factors
that exist in critically ill patients and predispose
them to VAP are illustrated in this case study.
Mr. D is a 75-year-old man
who came to the emergency department on May 13, 1997,
with a chief complaint of crushing chest pain. His
medical history included hypertension, chronic
obstructive pulmonary disease, diverticulitis,
cerebrovascular accident, previous myocardial
infarction, left carotid endarterectomy, and mental
status changes consistent with dementia and organic
brain syndrome. Despite the mental status changes, the
patient was able to engage in activities of daily
living. Daily medications at admission were one aspirin
tablet daily and nitroglycerin tablets as needed for
chest pain.
Mr. D was admitted to the
coronary care unit for a cardiac work-up. On May 16, he
underwent a cardiac catheterization that revealed severe
aortic stenosis and one-vessel coronary artery
occlusion. He underwent cardiac surgery on May 19 for an
aortic valve replacement and a single vessel coronary
artery bypass graft. Surgery was uneventful, and Mr. D
was transferred to the cardiothoracic ICU. He was
intubated and mechanically ventilated in the ICU and had
a pulmonary artery catheter and nasogastric tube in
place. Postoperative medications included 750 mg
intravenous vancomycin daily, 150 mg ranitidine liquid
by nasogastric tube every 12 hours for four doses,
morphine sulfate for pain, and midazolam as needed for
sedation.
Mr. D’s postoperative course
was difficult. He was unable to wean from the ventilator
and required a short-term neuromuscular block to manage
his respiratory status. "Coffee ground" gastric drainage
developed on May 21, and antacids were administered
every 4 hours. Metoclopramide was administered to
increase gastric motility. On May 21, a right upper lobe
infiltrate was noted on chest radiograph. A sputum
culture from May 20 grew Streptococcus. Tympanic
temperature increased to 100.9 F. Intravenous
ceftazidime was added to the medication regimen.
On May 22, a small-bore
nasal enteric tube was introduced for feeding, and
postpyloric placement was confirmed. Continuous tube
feedings were initiated. The right lung infiltrate
worsened, and temperature increased to 101.9 F. His
white blood cell count, which had been normal, increased
to 12,800/mm3.
A second sputum culture showed
Enterobacter cloacae.
Metronidazole hydrochloride was added to the other two
antibiotics.
On May 27, an infectious
disease consultation was obtained, and a diagnosis of
nosocomial pneumonia was confirmed. Antibiotics were
changed to intravenous ciprofloxacin hydrochloride and
imipenem, because the bacteria were reported to be
B-lactum resistant. A computed tomographic scan of the
sinuses revealed findings consistent with sinusitis.
The patient underwent a
tracheostomy and jejunostomy on May 30. Both nasal tubes
were removed, and jejunal feeding was initiated.
Gradually Mr. D’s symptoms improved, and he was weaned
from the ventilator. Approximately 1 month after
surgery, he was awaiting transfer to a rehabilitation
facility.
Several questions are posed
for the clinician’s and the APN’s critical analysis:
Identify the many risk factors that predisposed him to
VAP. How could the antibiotic treatment have affected
his clinical course? What factor(s) other than pneumonia
could have caused the initial abnormal chest radiograph
finding? What nursing actions may have prevented Mr. D
from getting pneumonia in the first place?
Summary
Ventilator-associated
pneumonia is a serious problem in the critically ill
patient. Nurses can be instrumental in preventing
pneumonia in the first place, recognizing symptoms,
assisting with diagnosis, and decreasing risk factors.
The APN must coordinate
Adapted from
Nursing Strategies to Prevent Ventilator-Associated
Pneumonia
Nursing Strategies to Prevent Ventilator-Associated
Pneumonia
Shelby Hixson, RN, MSN,
CCRN; Mary Lou Sole, RN, PhD, CCRN, FAAN; Tracey King,
RN, BSN, CCRN
