Yield of Percutaneous Needle Lung Aspiration in Lung Abscess: DISCUSSION
Securing bacteriologic confirmation of the microorganisms responsible for a lung abscess implies the need for invasive methods of obtaining samples of bacteriologic study in most patients. This need is determined by nonvalidity of sputum and any other specimen subjected to contamination by normal flora of the upper airways, the low diagnostic accuracy of blood cultures, and the low frequency with which these patients initially present with an associated empyema.
The diagnostic method employed most frequently has been transtracheal aspiration. Its accuracy in bacteriologic diagnosis has been superior to 80 percent with a very low number of false-negative results in patients who have not been previously receiving antibiotic treatment. The specificity of the results obtained with this technique have not been established clearly, although it is supposed to be high. This statement is based on the principle that the bronchial tree is sterile beyond the vocal chords, and thus, any bacteria cultured in the samples obtained by this method would represent the authentic causative microorganism. Today there is proof that this principle is not fully accurate. It has been demonstrated that patients with chronic bronchitis and bronchiectasis, with bronchial neoplasms, or those under frequent therapeutic orotracheal aspiration may harbor elevated concentrations of bacteria, generally aerobic, in their lower airways without clinical signs of pulmonary infection. Even normal individuals, up to 20 percent, may show aerobic bacteria in their tracheal aspirates in small concentrations, according to Berman and associates. tadalis sx
Recently, there has been interest in obtaining bronchial secretions by fiberoptic bronchoscopy using a double catheter brush system with telescoping cannulas and distal occluding plug. The specificity of this method is based on the same principle applied in transtracheal aspiration, although it carries with it the additional drawback of offering only a small amount of material for culture. Reported experience with this method in patients with lung abscess has been limited, with small series of patients, and similar or inferior results to those achieved with transtracheal aspiration.
In recent years, PLA has been employed only sporadically. The largest reported series is that of Beerens and Tahon-Castell, who achieved a bacteriologic accuracy of 79 percent in their cases. Our results using a thin needle have been slightly superior, with an excellent sensitivity in those patients who have not been receiving previous antibiotic treatment (92 percent), and even very good sensitivity (70 percent) in those patients who did receive antibiotics prior to performance of the technique. This high sensitivity has been obtained by prompt processing of the samples and by using fluoroscopic guidance, which ensured that the LA is obtained from within the cavitation. In fact, our only two false-negative results not attributable to previous antibiotic treatment may be imputed to lack of fulfillment of these two previous premises.
The specificity of the results achieved with this technique is superior to those obtained with transtracheal aspiration. The results with consecutive use of both techniques in the experimental model of pneumococcal pneumonia reported by Moser et al or the series of ten cases of lung abscess reported by Irving et al prove this. The only chance of false-positive results with this method derives from the possibility of contamination of LAs with flora of the skin, which is easily obviated with adequate disinfection. This lack of false-positive results eliminates misunderstanding in the evaluation of results offered by culture of transtracheal aspirates, especially when it is applied to patients with the previously specified chronic pulmonary diseases or bronchogenic carcinoma associated with the abscess. Also, it is of great aid to establish the certainty of bacteriologic diagnosis of unexpectedly unusual association of microorganisms, as occurred in our case with H parainfluenzas and M tuberculosis. levitra plus