Inflammatory airway disease: When, how to perform a bronchoalveolar lavage

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
Nov 01, 2008

Inflammatory airway disease (IAD) describes an interrelated set of diseases of the lower airway of horses that encompasses infectious, inflammatory, obstructive, hyper-reactive and allergic etiologies.

Clinical signs and physical findings of IAD may be overt and include respiratory distress, tachypnea, cough, mucoid nasal secretions, nasal flaring, abdominal lift on expiration and the presence of adventitious sounds (i.e., crackles or wheezes). However, often the signs are subtle and obscure, only manifesting as reduced performance or prolonged recovery after exercise.

A bronchoalveolar lavage (BAL) is a diagnostic test that is easy to perform in the field and provides specific information about the presence of lower airway disease in horses.

In this article, we will discuss indications for performing a BAL, how to do it and interpret your results.

Why perform a BAL?

There are two major ways to retrieve a sample of fluid from the lower airway of the horse: transtracheal or endotracheal.

In either procedure, saline is instilled into the lower airway and a sample is aspirated. With the trans- tracheal aspirate or wash (TTA or TTW) procedure, the hair over the mid to distal cervical trachea is clipped and the skin is surgically prepared. After local instillation of subcutaneous lidocaine, a sterile, bevel-tipped cannula is inserted through the trachea, serving as an entrance guide for a sterile catheter that is subsequently used to instill the saline.

The main advantage to a TTA is that the sample was instilled and retrieved under sterile conditions; thus it is the preferred method when a culture of the aspirate is indicated.

The main disadvantages of a TTA are that the hair is clipped and the trachea is invaded percutaneously. Since the procedure recovers fluid from within the trachea, the cyto- logy may not truly reflect disease of the smaller airways until that disease process is severe.

Subtle signs: IAD may be hard to detect at times, perhaps manifesting as slow recovery from exercise.
In the endotracheal method, saline is instilled either through a bronchoscope that is passed into the level of the trachea, or 3 m endoscope or long flexible BAL tubing (3-m length, 10-mm OD silicone tube; BAL catheter by Bivona Medical Technologies, Gary, Ind., or Cook Veterinary Products Inc., Bloomington, Ind.) that is passed further to the level of the segmental bronchi, via the nasopharyngeal passage (Photo 1).

The main advantage to the endotracheal procedure is that, with long tubing such as the BAL catheter, the small airways and alveoli can be reached and cytologic examination may more accurately reflect those areas.

A BAL is particularly helpful when looking for subtle disease of the small airways. If using a 3-m endoscope for the lavage, the scope may be directed into either the right or left main stem bronchus.

When "blinding" (passing a BAL tube from the nasopharynx), the tube typically ends up in the right dorsal lung lobe; thus focal small-airway disease in other regions may be missed.

How to do a BAL

A BAL should not be performed on a horse with overt respiratory distress, tachycardia or evidence of pulmonary hypertension.

The BAL tubing is sterile and can be resterilized between patients; however, since the procedure involves passing the tubing through the upper airway, retrieved samples are not sterile and culture results will not be accurate.

Horses will cough violently during the BAL procedure, and thus moderate to heavy sedation with xylazine (250 to 400 mg/1,000 pounds body weight IV) or detomidine (3 to 10 mg/1,000 lbs IV) is needed. Addition of butorphanol (3 to 5 mg/1,000 pounds IV) or 450g of inhaled albuterol may also help suppress the intensity of the cough reflex. In some patients a twitch may be necessary.

Before the BAL tube is passed, the cuff should be checked, and a small amount of sterile lubricant should be applied to the tip.

Photo 1: A 3-m bronchoalveolar tube. The cuff at the distal tip was checked by inflation with 5 ml of air at the injection port (syringe) prior to using.
The BAL tubing is passed through the nasopharynx via the ventral meatus using the same technique as when passing a nasogastric tube. When the BAL tubing reaches the level of the laryngeal orifice, instillation of 10 to 20 ml of 0.3 percent to 0.5 percent warm lidocaine may ease the intensity of the gag and coughing reflex.