Comparison of Blind Endotracheal Aspiration and Bronchoscopic Brush Biopsy Sampling Methods for Bacteriological Diagnosis of Ventilator-Associated Pneumonia in Intensive Care Unit.

BACKGROUND: The diagnosis of ventilator-associated pneumonia (VAP) is a challenge because the clinical signs and symptoms lack both sensitivity and specificity. Further confirmation of the diagnosis of VAP can be done by other diagnostic procedures such as bronchoscopic and blind endotracheal aspiration, but the selection of either diagnostic procedure is debatable. AIMS: The aim is to study and compare the role of bronchoscopic protected specimen brush biopsy (PSBB) and blind endotracheal aspiration for diagnosis of VAP. SETTINGS AND
DESIGN: This prospective comparative study was conducted in multidisciplinary Intensive Care Unit of a tertiary care hospital.
MATERIALS AND METHODS: Thirty patients clinically diagnosed to have VAP were further evaluated by bronchoscopic and blind endotracheal aspiration. The P value of PSBB and blind aspiration techniques was calculated, taking clinical pulmonary infection score of ≥6 as reference standard. STATISTICAL ANALYSIS USED: Statistical analysis was done using Chi-square and t-test. RESULTS AND
CONCLUSIONS: Our study shows that for the diagnosis of VAP, PSBB and blind aspiration had Chi-square value of 0.83 with degree of freedom 1 which showed P = 0.3623 which is not significant. t-test value is 0.402 with degree of freedom 1 and P = 0.7567 which is still not significant. There was a good microbiologic concordance among bronchoscopic and nonbronchoscopic distal airway sampling techniques. Blind endotracheal aspiration is a comparable technique for bacteriological diagnosis of VAP.

INTRODUCTION

Ventilator-associated pneumonia (VAP) is defined as an inflammation of the lung parenchyma occurring 48–72 h or more after tracheal intubation, due to microorganisms neither present nor incubating at the time of starting mechanical ventilation.[1] It is the most common nosocomial infection encountered among the intubated patients in the Intensive Care Unit (ICU) with incidence varying between 9% and 28% in developed countries.[23] In India, the incidence of VAP was 28.04% and mortality in VAP group was 46.67%.[4]

The combination of impaired host defenses and continuous exposure of the lower respiratory tract to large numbers of potential pathogens through endotracheal tube makes the mechanically ventilated patient prone to developing VAP.

Common pathogens causing VAP includes aerobic Gram-negative bacilli, such as Pseudomonas aeruginosa, Escherichia coli, Klebsiella pneumoniae, and Acinetobacter species. Infections due to Gram-positive cocci, such as Staphylococcus aureus, are more common in patients with diabetes mellitus and head trauma.[5]

The diagnosis of VAP remains a challenge because the clinical sign and symptom lack sensitivity as well as specificity, and the selection of microbiological diagnostic procedure is a matter of debate.[6] Clinically, VAP is defined by four criteria: radiographic appearance of new or progressive pulmonary infiltrates, fever, leukocytosis/leukocytopenia, and purulent tracheobronchial secretions.[7] However, each of these signs or symptoms taken separately has limited diagnostic value and may also be seen in a noninfectious process.[89]

Pugin et al.[10] combined body temperature, white blood cell count, volume and appearance of tracheal secretions, oxygenation (PaO2/FiO2), chest X-ray, and tracheal aspirate cultures into a clinical pulmonary infection score (CPIS) as a diagnostic tool for VAP and found that a CPIS of >6 was associated with a high likelihood of pneumonia with a sensitivity and a specificity of 93% and 100%, respectively.

Accurate clinical and microbiologic diagnosis of VAP helps in selection of appropriate antimicrobials and prevents misuse of antimicrobials leading to antibiotic resistance.

It has been postulated by numerous investigators that “invasive” diagnostic methods, including quantitative cultures of distal airway specimens obtained using bronchoscopic bronchoalveolar lavage (BAL), bronchoscopic brush, protected BAL, or protected specimen brush biopsy (PSBB), could improve identification of patients with true VAP and selection of appropriate antibiotics.[1112] However, bronchoscopy requires technical expertise and adds to the cost of care. The results of the studies using bronchoscopic techniques are inconsistent, showing both false-positive and false-negative results, which further question their exact role in the diagnosis of VAP.[1314]

MATERIALS AND METHODS

A prospective controlled trial was conducted in ICU of our hospital after Ethical Committee Approval. Patients between 18 and 65 years of age, requiring mechanical ventilation for >48 h and who qualify the criteria of VAP were enrolled for the study after written and informed consent.

Exclusion criteria of this study were as follows: community-acquired pneumonia, active chest infection, immunocompromised state, bleeding diathesis, in shock requiring more than one inotrope, or who had aspiration.

During this study, to prevent nosocomial infection, infection control policy was implemented in our ICU. All the patients after 48 h of mechanical ventilation were followed up for next 7 days, and CPIS was done for diagnosis of VAP every alternate day. VAP was considered to be present when modified CPIS scoring >6 [Table 1].

Table 1

Clinical pulmonary infection score>6 considered to be positive

In patients who qualify the criteria of VAP as per CPIS scoring, two samples of endotracheal aspirate by both blind double catheter technique and bronchoscopic PSBB were taken. Blind endotracheal aspiration was done in all patients before bronchoscopic brush biopsy, to avoid the contamination of the lower airways.

Blind double catheter technique (noninvasive) was done by two persons with all aseptic precautions. Distal 5–6 cm portion of large-bore suction catheter size 16 FrG was cut by a sterile surgical blade. Three-fourth length of a small-bore catheter size 8 FrG was introduced into the large catheter. Endotracheal tube was disconnected from the ventilator, and the set of catheters was introduced into the endotracheal tube by no-touch technique. When the larger catheter got wedged in the trachea, small catheter was introduced further, and suction was applied. As soon as aspirate was seen in the catheters, suction was stopped, and small-bore catheter was taken out without touching its tip and flushed with 1 ml of normal saline into the sterile container [Figure 1].

Figure 1

Blind endotracheal aspiration sampling by double-catheter technique

For bronchoscopic PSBB (invasive), a patient was sedated with injection midazolam 2 mg and injection fentanyl 30 μg intravenously. The ventilator settings were changed by increasing the tidal volume by 100 ml and FiO2 to 1.0. Hemodynamic parameters including heart rate, blood pressure, and oxygen saturation were monitored continuously during the entire procedure. The fiber-optic bronchoscope was introduced through the T-piece, and the tip was positioned close to the orifice of the bronchus, draining the bronchopulmonary segment of interest as determined by chest radiograph. In patients with diffuse/bilateral lung infiltrates, bronchoscope was advanced into a bronchopulmonary segment of the right lower lobe for sampling. After introducing the bronchoscope and wedging the tip in the selected segmental or subsegmental bronchus, Bronchoscopic protected specimen brush was introduced with the sheath. After reaching the selected segment or subsegmental bronchus, the brush was taken out from sheath and swirled in the lung tissue 2–3 times. It was then inserted back in sheath and taken out. The brush was vortexed in 1 ml of normal saline taken in a sterile container [Figure 2].

Figure 2

Protected specimen biopsy brush

Both the samples were blinded and transported to microbiology laboratory within 1 h of collection of sample. In the laboratory, the samples were processed and the colony-forming units per milliliters (CFU/ml) were noted for both the samples.

The cultures were considered to be significant when the CFU/ml was >104. If CFU/ml was <104, then the culture was considered nonsignificant or subclinical as per the hospital protocols.

RESULTS

Thirty patients positive for VAP by CPIS >6 were included in the study.

As both the tests were done on the same patients, there was no bias due to sex or age distribution [Table 2].

Table 2

Distribution

VAP was diagnosed by CPIS >6 in 60% of patients on the 7th day of onset of mechanical ventilation and on the 5th day in 23.3% of the patients. On the same day, the samples were sent to the microbiological laboratory for the evaluation of both invasive and noninvasive test.

Out of 30 patients, bronchoscopic PSBB culture reports showed significant bacterial growth in 26 patients (86.6%). Samples obtained by blind aspiration showed significant growth in 27 patients out of 30 patients (90%) [Table 3 and Graph 1].

Table 3

Comparison of two methods

Graph 1

Comparison of both methods

On applying Chi-square test using a 2 × 2 contingency table and the degree of freedom being 1, the value of Chi-square comes out to be 0.83 with a P = 0.3623 that is statistically nonsignificant. On further applying t-test, T value is 0.402 and the degree of freedom being 1, P = 0.7567 which is also nonsignificant. This implies that the noninvasive method of blind double catheter technique is equally effective as compared to the bronchoscopic PSBB for the diagnosis of VAP [Table 4].

Table 4

Statistical analysis

In this study, during the analysis of bacteriological culture, we found that one patient was negative for both blind aspiration and PSBB, as no bacterial pathogen was isolated from that patient. Among 19 (out of rest 29 patients), Acinetobacter baumannii was isolated in 19 patients (65.51%), followed by P. aeruginosa in 17.24% (5/29), S. aureus in 10.34% (3/29), and K. pneumoniae in 6.89% (2/29).

DISCUSSION

VAP is a common complication associated with invasive ventilatory support and contributes to significant morbidity and mortality in these patients.[715] Because of poor specificity of the clinical diagnosis of VAP, reliance is often placed on radiological and microbiological diagnosis.

Endotracheal aspiration (single-catheter technique) is the most commonly used method of endotracheal sampling in ICUs all over the world. It requires little technical expertise and no specialized equipment or technique. However, this technique has low sensitivity and specificity for the diagnosis of VAP, as the upper respiratory tract is frequently colonized with potential pathogens, even in the absence of pneumonia.[1617]

Various studies have shown that bronchoscopic procedures are important part of evaluation of patients with VAP. However, these are associated with false-positive and false-negative results.[181920]

Canadian Critical Care Multicentric Trial group,[20] demonstrated that there was no statistically significant difference in clinical outcome among patients treated for VAP based on bronchoscopic or nonbronchoscopic procedures.

In developing countries, bronchoscope facility is not routinely available for patients admitted in ICU. Therefore, it is important to evaluate the role of nonbronchoscopic techniques in India.

The present study comparing blind endotracheal aspiration and bronchoscopic PSBB has shown that blind technique is comparable with the bronchoscopic PSBB. Inherent advantages of nonbronchoscopic techniques include no instrumentation, lesser compromise of oxygenation, ventilation and respiratory mechanics during the procedure, less likelihood of increasing intracranial pressure and arrhythmias, lack of contamination through the bronchoscopic channel, and lower cost.

Although it is a blind procedure, its concordance with bronchoscopic brush proves the fact that protected sample adequately represents the lower airway secretions and efficiently diagnoses VAP. The utility of blind aspiration for diagnosis of VAP has been demonstrated by other researchers also, both in clinical as well as autopsy studies.[1019]

Pugin et al. used CPIS as the diagnostic criteria for VAP and found that sensitivity, specificity, and positive predictive value of nonbronchoscopic blind aspiration were 73%, 96%, and 92%, respectively.[10]

Khilnani et al. showed bronchoscopic brush had a sensitivity of 94.9% and specificity of 57.1%. Sensitivity and specificity for blind endotracheal aspiration were 83.3% and 71%, respectively.[21]

Many other researchers also have shown that blind technique has high sensitivity (70%–90%) and specificity (69%–100%) depending on the criteria used to diagnose VAP.[102223]

Till date, the optimal strategy for the diagnosis of VAP remains to be defined.

The American Thoracic Society guidelines provide expert opinion supporting quantitative or semi-quantitative cultures of respiratory specimens, although the panel favors invasive quantitative techniques.[14]

Our study has shown that blind technique is an acceptable alternative to bronchoscopy for the evaluation of suspected VAP. P value determined by both Chi-square test (P = 0.3623) and t-test (P = 0.7567) was found to be nonsignificant.

CONCLUSIONS

The study has shown that blind aspiration technique is comparable with the bronchoscopic PSBB. However, there are some inherent advantages of blind aspiration technique due to which we recommend the use of blind endotracheal aspiration method over bronchoscopic PSBB as the technique of choice in the bacteriological diagnosis of VAP.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.