Comparison between BAL, mini-BAL and bronchial wash.
Currently there are no studies designed to compare the diagnostic yield
and complications of BAL, mini-BAL and bronchial wash. BAL consists in
the instillation of approximately 120ml of saline solution with the
flexible scope wedged into a segmental bronchus. This technique allows
to collect the distal (broncho-alveolar) cellular and acellular
component of the lung. The instillation of at least 100ml of saline
solution is required to reach the alveolar component and achieve a BAL
of sufficient quality for microbiology, cytology, immunological and
molecular studies.41 For patients with severe
respiratory failure or poor general conditions bronchial wash or
mini-BAL are possible alternative methods for microbiology studies.
Bronchial wash collects the bronchial component and is performed with
approximately 20ml of saline solutions within the main or lobar bronchi.
This technique does not allow to study the alveolar component but given
the lower instilled volume it is considered to be less invasive compared
to BAL. Mini-BAL is poorly standardized. Has been reported as the
instillation of a variable volume of saline solution (between 20 and
60ml) using either the bronchoscope or a blind catheter advanced into a
distal airway.42,43As for bronchial wash this
technique is suitable for microbiologic studies, but not to study the
alveolar component. Given the variability of the technique used in
different studies it is difficult to evaluate the diagnostic accuracy of
this techniques, but they are all reported to have a good safety
profile.
In COVID-19 intubated patients mini-BAL has been described in at least
two studies. Vanbellinghen et al retrospectively compared the prevalence
of aspergillosis in COVID-19 diagnosed using mini-BAL (20ml of saline
instilled through a blind catheter) to that of BAL.42The Authors performed mini-BAL in 40 cases, BAL in 20 and both in 16
cases, showing a good agreement between the two methods and a similar
prevalence of overall positive Aspergillus results using PCR
and/or galactomannan and/or culture (16.7% BAL and 21.4% for
mini-BAL).42 Torrego et al performed mini-BAL in 63
severe COVID-19 patients (all intubated, PaO2/FiO2 111, IQr 103-125)
instilling 60ml of saline with a wedged scope according to the
radiological features.43 One third were performed in
prone position. They had 28.6% (18/63) of positive microbiology
results, with a profile of pathogens similar to what observed in a
retrospective pre-COVID-19 cohort of patients seen at their centre
(Pseudomonas aeruginosa n = 7, Staphylococcus aureus n =
2, Klebsiella aerogenes n = 2, Enterobacter cloacae n = 2,Enterococcus faecalis n = 2, Escherichia coli n = 1,Streptococcus anginosus n = 1, or Prevotella
melaninogenica n = 1).43
To the best of our knowledge, only Mondoni et al. published a
retrospective study that attempted to compared BAL to bronchial washing
(BW) in suspected COVID-19 non critically ill patients. The Authors
reported an overall diagnostic yield for SARS-Cov-2 detection of 55%
(43/78), 57% (35/61) with BAL and 47% (8/17) with BW, statistical
difference wasn’t reached (p=0.45).
All these bronchoscopy procedures are similarly well tolerated, but
safety studies designed to compare these different methods are lacking.