Bronchoalveolar Lavage, or BAL as it is commonly known, is a minimally invasive procedure that involves instillation of sterile normal saline into a subsegment of the lung, followed by suction and collection of the instillation for analysis. This procedure is typically facilitated by the introduction of a flexible bronchoscope into a sub-segment of the lung. The procedure as we know it today was popularized in 1974 by the work of American physicians, Reynolds and Newball, in Maryland. Today, it serves predominantly as a diagnostic tool for the evaluation of lower respiratory tract pathology and in some uncommon conditions, also has therapeutic utility.
Even though the collection of BAL samples is not standardized, experts suggest following a protocol to minimize contamination and artifacts. The recovered lavage fluid should be pooled, mixed and the volume recorded. The fluid should be sent to the laboratory while stored on ice if the transportation is going to be delayed by more than 1 hour. Studies show that cells in BAL fluid can remain viable for 4 hours at room temperature. The fluid is usually analyzed for white and red cells. To distinguish immature macrophages from large lymphocytes, esterase staining is employed. Other stains may evaluate for the presence of iron, malignant cells, inorganic dust, and microorganism. In general, if the BAL specimen contain less than 2 million total cells or has fewer than ten alveolar macrophages per high power field, or contains a high number of red cells (due to trauma) or there are degenerative changes, the specimen should not be relied upon to make any valid diagnosis. Of note, the average number of cells recovered from BAL fluid in healthy nonsmoking adults varies from 100-150,000/ml. Smoking increases the number of cells by 4-6 fold, of which most are macrophages.
A significant portion of pathological disease within the lungs occurs at the alveolar level. BAL allows for the collection of the alveolar milieu and further analysis of its composition. Common scenarios for the use of BAL include work up for opportunistic and atypical respiratory infections in immunocompromised patients, unexplained radiographic pulmonary infiltrates or hypoxemia. BAL can also provide clues to support the diagnosis of some noninfectious conditions such as Diffuse Alveolar Hemorrhage (DAH), Pulmonary Alveolar Proteinosis (PAP), Eosinophilic Pneumonia, Hypersensitivity Pneumonitis (HP), Interstitial Lung Diseases (ILDs), chronic berylliosis, the presence of malignant cells and Asbestos exposure.
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 the 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.
If a localized disease process predominates, usually identified on radiological imaging (e.g., , henceChest X-ray or Computed Tomography (CT) of the Chest), then the bronchoscope is guided to that specific region and wedged into the subsegment with visualization of the distal airway ideally in the center of the image. If diffuse, (the heterogeneous disease is present on imaging), the most commonly preferred locations for lavage would be the right middle lobe or lingula. As bronchoscopy is usually performed with the patient lying supine, the anteriorly projected location of these segments allows gravity to assist with maximal BAL. Hence we prefer these sites. If these segments are not accessible, the superior or anterior segment of either lower lobe may also be used. In theory, this process enables lavage of up to 1 million alveoli.
Similar to any flexible bronchoscopy, awareness of toxicity and side effects of medications given for conscious sedation (e.g. midazolam, propofol, fentanyl, etc.) and cough suppression (topical lidocaine) is necessary.
When taking the history, ensure that there are no contraindications to bronchoscopy for the purpose of BAL, such as myocardial infarction within the past four weeks or unstable angina, hemodynamic instability, uncontrolled arrhythmias and refractory hypoxemia.
Taking note of smoking status and exposure history is also important to give the substantial effect smoking has on the cellular composition of BAL, namely many more neutrophils and macrophages than in nonsmokers.
The paucity of good evidence to support specific values for a normal BAL, leaves us to pay attention to specific cell line cut offs that certain support diagnoses such as:
Progressively darkening aliquots of bloody BAL fluid is highly suggestive of DAH. Hemosiderin laden macrophages can also be evident on BAL analysis.
If chronic berylliosis is suspected, a positive lymphocyte proliferation test will be positive.
BAL is an excellent method of obtaining specimens to rule out opportunistic infections in immunocompromised individuals. It is important to combine culture results with cytology which may show viral intranuclear or intracytoplasmic inclusion bodies on examination of pulmonary epithelial cells. this may help identify viruses like herpes simplex and CMV. BAL is also very useful for detection of fungi and mycobacteria which may not always be identified in blood. The one big disadvantage of BAL is that many potentially pathogenic microorganism may have colonized the airways in the absence of any clinical disease and hence their recovery may not be meaningful.
The use of BAL has been extensively studies in patients with interstitial lung disorders like hypersensitivity pneumonitis, sarcoidosis and idiopathic pulmonary fibrosis. Unfortunately the findings of BAL are frequently not specific for these lung disorders and thus, the physician must also incorporate the clinical and imaging findings before making the diagnosis. In some disorders like acute eosinophilic pneumonia, BAL has saved the patient an unnecessary lung biopsy
BAL is also proving to be useful in evaluating individuals with occupational exposures to asbestos and other silicates. These macrophage ingested occupational dust particles is usually visible in the fluid under polarized light. BAL cytology is also useful for evaluating patients with malignancies of the airways.
For the most part, BAL is performed for diagnostic purposes. However, BAL is uniquely used for the treatment of pulmonary alveolar proteinosis. This involves instilling 30 to 50 liters of sterile saline through a double lumen endotracheal tube while the patient is under general anesthesia.
The most common risks of the procedure are similar to those seen in flexible bronchoscopy. They include transient hypoxemia, post-BAL fever (seen in up to 30% of patients), bronchospasm, and very rarely pneumothorax. Given the low incidence, routine chest x-ray after the procedure is not performed unless clinically indicated.