Inflammatory airway disease: When, how to perform a bronchoalveolar lavage - DVM
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Inflammatory airway disease: When, how to perform a bronchoalveolar lavage
This diagnostic test for IAD is relatively easy for practitioners to perform in the field


DVM360 MAGAZINE


Extension of the head will facilitate passage of the BAL tube from the pharynx into the trachea. The tubing is advanced slowly until it wedges in the small airways (noted by gentle resistance). Some individuals will also instill an additional 10 to 20 ml of 0.3 percent to 0.5 percent lidocaine when the tube reaches the level of the carina.


Photo 2: A fluid pressure sleeve may be used to instill the saline through the BAL tubing.
Once the tubing is wedged, the cuff is inflated (typically about 5 ml of air) and the tube is held securely at the nares. At this point, approximately 250 ml of warm isotonic (0.9 percent) saline is rapidly infused into the BAL tubing. One may accomplish this either by bolusing 60 ml luer-tipped syringes of saline or by attaching a 500-ml to 1-liter bag of saline to a fluid administration set and applying pressure to the exterior of the bag manually or with a fluid bag pressure sleeve (Photo 2). Wait 5 seconds, and then aspirate fluid, using 60-ml syringes.

The aspirated fluid should appear foamy from the presence of surfactant. Not all of the instilled fluid will be recovered, but typically at least 50 percent of it is retrievable. A second aliquot of 250 ml of saline is instilled and aspirated. Subsequently, all sets of the aspirated fluid are pooled. The cuff should then be deflated and the tubing removed.


Figure 1: Cytology of BAL fluid from a young horse with inflammatory airway disease. 1=macrophage, 2= lymphocyte, 3= neutrophil, 4=eosinophil.
Serious complications associated with the BAL procedure are rare, though intense coughing in horses with pulmonary hypertension may result in clinically significant hemorr- hage from pulmonary vessels. A transient low-grade fever or mild depression after a BAL also are reported rarely.

The pooled fluid should be mixed gently by swirling, and aliquots (approximately 10 ml) of the pooled fluid should be transferred to EDTA tubes for laboratory analysis.

If a clinical pathology laboratory cannot process the samples within a few hours of collection, the sample should be placed on ice or refrigerated.


Figure 2: Cytology of BAL fluid from a horse with recurrent airway obstruction. 1=macrophage, 2= mast cell. There is an Alternaria spore within one of the macrophages (arrow). The presence of fungal spores is not unexpected in horses with inflammatory lung disease because the inhaled spores become trapped within excessive mucus secretions and inflammatory debris.
Although the protein in the surfactant should be sufficient to preserve the cells, delayed processing can significantly affect cell morphology and thus addition of serum (10 percent v/v), an equal volume of ethyl alcohol or an equal volume of 100-proof vodka is indicated.

If laboratory processing will be delayed more than 24 hours, preparation of air-dried samples is recommended. Because of the dilutional effect of the saline, BAL samples must be cytocentrifuged or concentrated for cytological examination.


Figure 3: Cytology of the BAL fluid from a mature horse with intense inflammatory airway disease, represented by the predominance of neutrophils. This horse had recurrent airway obstruction (heaves) with secondary infection, as indicated by the presence of bacteria intracellularly (arrowhead) and extracellularly (arrows).
Thus, to make a smear, first centrifuge 10 to 15 ml aliquots (600 g for 10 minutes) and decant the supernatant. Gently resuspend the pellet at the bottom of the tube with the remaining fluid using a plastic transfer pipette and transfer a drop to a clean slide. Smear the drop to a feathered edge, as is done when preparing a blood smear. The slide must be quickly air-dried by fanning. Numerous slides should be prepared because typically 500 cells or more are counted by cytologists for differential enumeration.


Figure 4: A Curschmann’s spiral (arrow) is a coiled plug of mucus extruded from the smaller airways and is a sign of chronicity.
Unless you are familiar with cytology of the lower airway, BAL fluid should be evaluated by a clinical pathologist. Using the previously described collection technique, normal BAL fluid contains predominately (40 percent to 70 percent) macrophages, 30 percent to 60 percent lymphocytes, less than 5 percent neutrophils, 2 percent mast cells and 1 percent eosinophils (Figures 1-4).

When a small volume of saline is instilled (< 250 ml) or if only a small volume of the saline lavage is retrieved (less than 50 percent of that instilled), the differential cell count may be affected and be less meaningful.

If the BAL tubing was not tightly wedged, respiratory epithelial cells may be present; however, the presence of large numbers of respiratory epithelial cells is expected in horses with viral infections of the respiratory tract.

As the percentage of neutrophils, mast cells or eosinophils increases above 5 percent, 2 percent and 1 percent, respectively, inflammatory airway disease should be suspected. However, it should be noted that, in mature healthy horses, up to 15 percent neutrophils could be present. In general, though, if neutrophils comprise greater than 15 percent of the BAL nucleated cell population in a mature horse, it would be considered highly supportive of a diagnosis of recurrent airway obstruction or heaves.

A predominance of lymphocytes has been reported in young racehorses with reduced performance. The etiologic origin and clinical significance of this finding is not entirely understood, though it has been suggested that increases in lymphocytes, without concurrent increases in neutrophils, mast cells or eosinophils, may represent a less intense or earlier form of respiratory tract inflammation.


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