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Over the last fifty years, mechanical ventilation has undoubtedly represented
an advance in the treatment of respiratory insufficiency. However, nosocomial pneumonia has emerged as a
leading complication of ventilation - increasing morbidity, mortality and
health care costs. Ventilator associated pneumonia (VAP) has been found to
have varying rates in different studies based on the population studied
and the type of diagnostic techniques used. While the incidence of VAP in
children, according to the data from hospitals enrolled in the National
Care and Safety Network, has been found to be as low as 2.3 per 1000
ventilator days in pediatric medical ICUs in the United States, VAP
continues to be the second most common health care associated infection
even in developed countries [1]. Two studies from India have shown
contrastingly high VAP rates of 32.5% and 20% in children ventilated in
Pediatric Intensive Care Units (PICU) [2,3]. In a recently published study
from a tertiary care center in north India, the incidence of VAP was
reported as 17.5/100 patients [4].
The diagnosis of VAP in children is challenging. While
early diagnosis is essential to improve the outcomes, there is also a
concern about accuracy of diagnosis to prevent overuse of antibiotics. The
gold standard for diagnosis is a combination of histopathology and culture
of lung tissue. However, this is not feasible in most children. In such a
scenario, one has to rely upon various combinations of clinical,
radiologic imaging and microbiologic criteria; the CDC criteria for
diagnosis of VAP include all these.
Clinical findings - fever, purulent secretions,
tachypnea, appearance of bronchial breath sounds, crepitations, and
worsening hypoxemia - have a poor sensitivity and specificity for
diagnosis of VAP [5]. These criteria are used only in combination with
imaging and microbiologic criteria. Appearance of new infiltrates, air
bronchograms, other findings suggestive of pneumonia, or progression of
infiltrates may suggest a diagnosis of VAP. However, the specificity of
such findings is poor; patchy atelectasis may give rise to similar
findings [6]. Microbiologic investigations have to be performed for the
confirmation of diagnosis of VAP in a child who is suspected to have
clinical and radiologic features suggestive of VAP. A variety of sampling
techniques like bronchoalveolar lavage (BAL), mini-BAL, and non-bronchoscopic
BAL, are feasible for the collection of samples for microbiologic
diagnosis. The commonly used sample of tracheal aspirate has poor
specificity.
To facilitate the diagnosis of VAP, a combination of
various parameters may be useful. The Clinical Pulmonary Infection Score
(CPIS) was developed by Pugin et al., [7] using a combination of
six clinical, radiologic, and microbiologic criteria: temperature, white
cell count, sputum, oxygenation, culture of tracheal aspirates, and
radiology; each parameter was scored from 0 to 2 and a total score of >6
points suggested a diagnosis of VAP. When compared to histopathology, 2
studies in adults reported the sensitivity of CPIS score as 72% and 77%,
while the specificity was 85% and 42% respectively [8,9]. There are
limited reports on the use of CPIS in children. A recent study evaluating
the closed-system suctioning reported on the utility of CPIS; the
difference in diagnostic rate using CPIS compared to CDC criteria was not
significant [10]. Similarly, another study reported good performance of
CPIS in comparison to BAL fluid culture [11].
The disadvantage of CPIS is the dependence on tracheal
aspirate gram stain and/or culture results which may be available only
after a waiting period of 24 to 48 hours; a ‘simplified CPIS’ may overcome
this [12]. This simplified score was used by the authors to identify early
in the hospital course of ventilator-associated pneumonia (VAP) which
patients are responding to therapy.
In this issue of the journal, Sachdev et al.,[13]
report the validation of ‘simplified CPIS’ for diagnosis of VAP in 30
children. Children with a ‘simplified CPIS’ of > 6 were suspected to have
VAP and underwent bronchoscopy and BAL. The diagnosis of VAP in these
children was confirmed based on a quantitative culture. The authors report
a sensitivity of 80%, specificity 80%, PPV 86.9%, NPV 70.5% and accuracy
80% at a cut-off score of 8. The authors provide useful evidence for the
use of a simple score to assist in the diagnosis of VAP. However, the use
of cut-off score of > 6 is based on CPIS and not ‘simplified CPIS’. It
will be desirable to have further studies enrolling larger numbers to
confirm utility of ‘simplified CPIS’.
There has also been an interest in various biomarkers
to assist in the diagnosis of VAP to optimize the therapy. Of these, serum
procalcitonin has been in the forefront, however, the results have been
varied [14]. Serial estimations of procalcitonin may assist in reducing
the duration of antibiotic therapy for VAP [14]. The search for optimal
biomarkers is on.
Competing interests: None stated
Funding: None.
References
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