Plugged telescoping catheter brush sampling

In 1979 Wimberley described a plugged telescoping catheter for use in sampling respiratory secretions ( Fagon et al 19.8.8.). This system was the most effective at resisting contamination in vitro when passed through a bronchoscope heavily contaminated with saliva. The bronchoscope is positioned at the appropriate bronchial orifice, the plugged telescoping catheter (e.g. Medi-Tech, Key-Med, United Kingdom) is advanced 2 cm into the segmental bronchus, and then the inner catheter is advanced a further 3 cm beyond the protecting plug. The catheter is then wedged and rotated to obtain the maximum innoculum of secretions. When sampling is completed, the brush and then the inner catheter are retracted and finally the whole catheter is removed. The outer and inner portions are cleaned, the brush is clipped off into 1 ml of sterile saline and transported rapidly to the bacteriology laboratory. The brush samples 0.001 ml; thus precise laboratory work is needed to obtain accurate quantitative results. In the absence of antibiotics, pathogens and contaminants can be distinguished by quantitative cultures containing more than 10 3 CFU/ml, although very recent infections may not yet have reached this pathogen load. Gram staining is not sufficiently accurate ( Nied.erm┬žn,eL.a/ 1994).

Animal models of pneumonia using quantitative cultures show a sensitivity of 70 to 90 per cent and a specificity of up to 100 per cent. In non-intubated patients protected brushing demonstrated organisms at a count above 103 CFU/ml in 95 per cent of those with definite pneumonia and in only 5 per cent of controls. False-positive results occur in patients with obstructing endobronchial lesions where distal growth of mixed flora occurs commonly without pneumonia.

Fagon etal (1988) obtained protected brushings and immediate postmortem lung biopsies from 26 patients with suspected nosocomial pneumonia. Of these, six had pneumonia histologically from which a total of 19 organisms were cultured, and brushing demonstrated 15 of these. In a second study by the same group only 45 of 147 patients with suspected pneumonia had more than 103 CFU/ml on quantitative culture of brush samples. Pneumonia was definitely excluded in only 9 per cent of these 45 patients. Brush samples from the remaining 102 patients had less than 103 CFU/ml and none of the patients were shown to have pneumonia. Pooled results of 18 studies of protected brushing show a sensitivity of 89 per cent (95 per cent confidence interval, 87-93 per cent) and a specificity of 94 per cent (95 per cent confidence interval, 92-97 per cent). Drawbacks include the persistent but low false-positive rate and the time between sampling and culture results. Potential false-negative results can occur if samples are taken from patients currently or recently on antibiotics, processed incorrectly, or taken very early in the course of the pneumonia when less than 103 but more than 102 CFU/ml may be cultured (Niederm.an et al 1994). Unlike lavage, brushing is not useful for diagnosing pulmonary pathogens such as Pneumocystis carinii or mycobacteria.

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