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Original Articles Indian Pediatrics 2000;37: 947-951 |
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Role of Gastric Lavage and Broncho - Alveolar Lavage in the Bacteriological Diagnosis of Childhood Pulmonary Tuberculosis |
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Manuscript received: September 7,
1999; Initial review completed: October 20, 1999;
Isolation of Mycobacterium tuberculosis is difficult in children with pulmonary tuberculosis as compared to adults where sputum is positive in upto two third of patients(1). Children with pulmonary tuber-culosis typically have closed caseous leasions with a relatively small number of mycobacteria. The large cavitary population of tubercle bacilli seen in adults is usually absent in children(2,3). This is compounded by the difficulty in collecting sputum in children as they swallow the expecto-rate coming from the lungs. To obtain the respiratory tract secretions procedures like gastric lavage (GL) and the bronchoalveolar lavage (BAL) have been used. Gastric lavage collects the respiratory secretions which are swallowed at night. Bronchoalveolar lavage samples the alveolar epithelial lining fluid directly and has been found to be useful in the diagnosis of several respiratory infections including tuberculosis(4). The isolation rate of Mycobacterium tuberculosis from GL cultures in children have been reported as 20-40%(5,6); it is higher in infants (upto 75%)(7). However, the reported culture positivity rate of BAL in all children is only 10-16%(8,9). Norman et al. reported that BAL is better than GL in the diag-nosis of pulmonary tuberculosis in adults(10) showing just the opposite that GL is better than BAL and BAL does not improve the isolation rate of Mycobacterium tuberculosis in children suspected of pulmonary tuberculosis. The present prospective study was undertaken to compare the yield of M. tuberculosis from gastric lavage and bronchoalveolar lavage from children with pulmonary tuberculosis.
Children with suspected pulmonary tuber-culosis in the age group of 6 months to 14 years, admitted in the Department of Pediatrics, PGIMER, Chandigarh over a period of two years were taken up for the study. Inclusion Criteria A provisional diagnosis of pulmonary tuber-culosis made in the presence of the following criteria was needed for inclusion of the patient in the study.
Gastric Lavage Gastric lavage was done on 3 consecutive mornings after an overnight fast with 30-35 ml of 0.9% saline and the lavaged specimen sent for staining and culture. A minimum of 30 ml of specimen was sent for analysis. Bronchoalveolar Lavage (BAL) Bronchoalveolar lavage was obtained by flexible fiberoptic bronchoscopy performed on the last day of gastric lavage by a trained person (MS). The procedure was explained to parents/guardians of all patients and patients more than 8 years of age. Informed written consent for the procedure was obtained from parents/guardian. All patients were monitored during the procedure clinically and by pulse oximetry for any complications. Patients were sedated with ketamine (1-2 mg/kg) and/or diazepam or midazolam (0.01-0.03 mg/kg). Supplementary oxygen was given during the procedure. Lignocaine jelly (2%) was applied to the nasal passage. The flexible fiberoptic bronchoscope (Olympus corporation Model BF3 C20) was inserted transnasally and 1-2 ml of 2% lignocaine was instilled at the larynx. No further lignocaine was used. The bronchoscope was advanced into the trachea and wedged into the most involved area as seen on the chest X-ray or into a segment of right middle lobe if infiltrate was diffuse. After wedging, 1-2 ml/kg (maximum 10 ml) of aliquots of sterile non bacteriostatic 0.9% NaCl solution was instilled through the suction channel of bronchoscope and subsequently aspirated by suction into a mucous specimen trap. After the lavage procedure, BAL samples were immediately submitted for staining and culture. Specimens from gastric lavage and BAL were digested and decontaminated with sodium hydroxide and N-acetyl L-cysteine. After buffering, samples were centrifuged at a rate of 3000 rpm for 20 minutes and the sediments were stained by Zeihl Neelsen technique for acid fast bacilli. After centrifuging, sediments were in-oculated into standard Lowenstein Jensen medium and incubated at 37-38°C for 6 weeks. The culture were checked weekly for any growth. The organism was identified by colony morphology and standard biochemical reactions(11). Statistical analysis included Chi-square and McNemar tests and statistical significance was defined as p <0.005. The study was approved by the Ethics Committee of Institute.
A total of 58 children were included in the study. The mean age was 6.2 ±2.57 years (range 6 months to 14 years). There were 32 boys and 26 girls. Eleven patients were less than 3 years of age with two infants less than one year. Forty two (76%) children were malnourished. Thirty three (57%) patients had received BCG in the first year of life. A contact case was identified in 32 (55%) patients. All patients except one were symptomatic at admission. The asymptomatic patient was a sibling of a patient. The common symptoms included cough (96%), fever (90%), failure to thrive (48%), and difficulty in breathing (16%). Eight patients (15%) had hemoptysis. A positive Mantoux reaction was observed in 40 (68.9%) patients. All patients with a negative Mantoux were malnourished (weight less than 60% of expected) grade III or below. Mantoux reacters were equally distributed between culture positive and culture negative cases. On chest radiography, thirty nine patients had segmental lesions in the form of collapse and/or consolidation. One of these patients also had pleural effusion. Primary complex was seen in 5 cases, cavitation in 2 and diffuse miliary infiltrate in 4 cases. Eight patients had paratracheal or hilar adenopathy on chest radiograph. All children underwent GL and BAL and tolerated bronchoscopy and BAL without any complications. Gastric lavage culture for M. tuberculosis was positive in 10 of the 58 (17.2%) patients and BAL in 12/58. In only two patients were GL and BAL both positive. Thus, there were 22 samples positive in 20 patients (34.5%). The difference in the recovery rates of Mycobacterium tuberculosis by GL and BAL technique was not statistically significant (p >0.05). Mycobacterial isolation rate increased from 17.2% to 34.48% by the addition of BAL to gastric lavage in the workup for tuberculosis (p = 0.013). There was no statistically significant difference (p = 0.48) in the age of children who grew M. tuberculosis on gastric lavage or BAL (GL = 6.9 ± 1.6 years, BAL = 6.1 ± 3.3 years). There was no significant difference in age and radiological lesions of patients in whom both BAL and GL were positive in comparison to those in whom only one of the investigations yielded positive result for M. tuberculosis. Taking culture positivity as the gold standard for confirming tuberculosis, the sensitivity of gastric lavage was 50% and that of BAL was 60%. Smear for acid fast bacilli (AFB) was positive in 4 patients only on GL specimens. All were subsequently confirmed by culture. Two of these patients had miliary tuberculosis and the other two had cavitary tuberculosis.
The results of this study indicate that both BAL and GL cultures are complementary to each other for isolation of Mycobacterium tuberculosis in children clinically diagnosed to be suffering from pulmonary tuberculosis. Mycobacterial isolation rate increased from 17% to 34% by addition of BAL as an investigation. These results are contrary to earlier reports (8,9) where gastric lavage proved better than BAL and BAL did not improve the yield of Mycobacterium tuberculosis. The first study with similar inclusion criteria as ours sampled 20 children and found that gastric lavage was positive in 10 (50%) patients and BAL in only 2 (10%) patients (gastric lavage cultures were also positive). Younger age (Mean age 2.5 years in comparison to 6.2 years in our study) could account for this difference. Starke and Taylor Watts(6) reported that infants with pulmonary tuberculosis have a higher yield of Myco-bacterium tuberculosis from gastric lavage samples (75%) than did older children with tuberculosis. This has also been confirmed by others(7). The method of collecting gastric lavage samples also affect the yield. Ideally, it is recommended that, the nasogastric tube be left in situ overnight and the contents have to be aspirated followed by a lavage, before the patient wakes up. Once the patient is awake, the gastric peristalsis increases and the gastric contents may not be available for analysis(12). The nasogastric tube could not be left in situ in most of our children because they were older and active and invariably pulled out the tube at night. In spite of this the positivity rate in our study is well within the reported limits(20-40%). In another study(8) out of the ten cases positive on GL only two had BAL positive for M. tuber-culosis. In the present study also only two patients had both the investigations positive for M. tuberculosis. A factor that can influence positivity of bacteria on GL is the timing of BAL. If GL is done after BAL there are more chances of GL being positive because BAL facilitates flux of secretions from the airways upwards which are swallowed into the stomach. This point however has not been discussed in the previous studies. In our study protocol, BAL was performed on one of the three days when GL was performed. Somu et al.(9) reported that of the 50 cases with suspected pulmonary tuberculosis, Myco-bacterium tuberculosis was grown in 6 (12%) BAL samples and 16 (32%) of the gastric lavage samples making a total of 17 (34%) culture proven cases. Out of the 6 BAL positive cases, gastric lavage was also positive in 5 cases. The rate of isolation of M. tuberculosis is similar in the present study but the proportion of patients positive on BAL are higher. The mean age in their study was 5.1 ± 3.8 years and the age group ranged from 7 months to 12 years. A reason for the higher yield of myco-bacteria in BAL in the present study could be BAL fluid centrifugation at 2500g which increases the recovery rate(13). All specimens were centrifuged at 3000 rpm for 20 minutes. On the contrary, in the study by Somu et al.(9) samples were decontaminated by modified Petroffs method, in which samples are centrifuged at 1500 g for 30 minutes. However, in the study by Abadco and Steiner(8) this was not a factor as they centrifuged the specimen at 2500 g. Some studies have suggested that anti-bacterial activity of lignocaine reduces the yield of Mycobacterium tuberculosis. Kvale et al.(14) reported that the culture of bronchial washings was negative in upto two third of their adult patients with pulmonary tuberculosis. They used a maximum 600 mg of lignocaine during the procedure and suggested that this accounted for the low recovery of mycobacteria in their patients. Most studies in adults which reported better yield with BAL used lesser amount of lignocaine (200-320 mg). Schmidt and Rosenkranz(15) have demonstrated the inhibition of Mycobacterium tuberculosis by varying concentrations of lignocaine. Lignocaine was used only at the time of entering the larynx to anesthetize the vocal cords and was not used after entering the trachea. This could have resulted in better yield with BAL in our study. In our study, midazolam or ketamine were used for conscious sedation which permitted a smooth performance of the procedure. The yield on smears for AFB from BAL fluid was nil. A low yield has been reported by previous studies also(8,9). This is possibly because of low bacillary load in childhood pulmonary tuberculosis. The detection of Mycobacterium tuberculosis by acid fast staining requires about 10,000 bacilli per ml of specimen which may not be available from BAL fluid of children due to closed caseous lesions. We conclude, when both GL and BAL are used for isolation of M. tuberculosis these procedures are complementary to each other. Bacterological yield is doubled by introduction of BAL in the diagnostic armamentarium.
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