The bronchoalveolar lavage (BAL) allows us to see deep within the horse’s lungs to determine if there is inflammation and if so, what does that inflammation look like? The BAL is sometimes called a lung wash, because we literally do wash the smallest airways and alveoli (tiny lung sacs where oxygen is exchanged) with sterile saline. When we suction back that fluid, we bring cells and mucus out of the lung, and then we make a cytology of that fluid – this means that we make a slide that we can look at under the microscope. The BAL can be done blindly in the field with a specialized silicone tube, called a Bivona BAL tube. This is a very useful technique, and is practical for ambulatory veterinarians. At Cummings, we prefer to do a full bronchoscopy. This allows us to examine all the airways as we obtain the BAL, and it also allows us to examine the upper airway to determine if there are any abnormalities that may be contributing to a horse’s cough or nasal discharge in addition to IAD.
Clients and referring veterinarians sometimes ask us why we don’t just do a tracheal aspirate using a regular endoscope. This is a very simple procedure, and doesn’t require any specialized equipment. The answer is that this method takes cells from what we term the ‘tracheal puddle’ toward the end of the trachea, and multiple studies have shown that what we see in the tracheal puddle does not reflect what we see in the BAL. Quite simply, the two methods are not equivalent, and the tracheal aspirate is inferior to the BAL if we want to know what is going on in the small airways – and this is what we care about with IAD horses.