Although societies such as American Thoracic Society and British Thoracic Society have published guidelines on the performance of BAL, there remains some variability in its performance. BAL is typically performed after introduction of the bronchoscope into the tracheobronchial tree and inspection of the airways but before any biopsies or brushings are collected. This minimizes the potential introduction of bronchial wall debris and additional red blood cells (RBCs) into the most distal airways, which could alter the composition of the lavage fluid. The outer diameter of adult flexible bronchoscope tips range between approximately 3mm-6mm, and the scope is guided into the subsegment of the lung that is to undergo BAL and advanced until the tip is wedged into a bronchiole.

Depending on local practice, anywhere from between 20 - 60 ml of room temperature, sterile normal saline is injected via handheld syringe and then gradually withdrawn back into the syringe. This is repeated 3-5 times, and a total of up to 300 ml is instilled. If only 5% of each aliquot injected returns - indicating that most of the injected fluid is being retained, the procedure should be aborted. A return sample yield of 30% or more of the instillate is considered an adequate return, of which at least 10 ml - 20 ml is required for cellular and infectious workup.