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.