3.7.1 Auscultation of lung fields
Auscultation of respiratory sounds requires quiet surroundings because abnormal sounds may be very subtle. Sounds may be harsh and dry, or suggestive of fluid movement within airways. Frequently, the most obvious abnormal sound is that of air flowing over a pool of fluid in the trachea at the thoracic inlet; it is important to include this area in auscultation.
An invaluable aid to auscultation is the use of a re-breathing bag. This simple technique results in much deeper respiratory movements than normal and accentuates sounds. A large plastic bag is placed over the nose and twisted so that there is a tight air seal. The bag should be held so that it does not occlude the nares during inspiration. The horse will start to breathe more deeply because of the build-up of carbon dioxide in the exhaled air which it re-breathes. The technique is tolerated remarkably well. Coughing and large quantities of mucoare produced on occasion, which illustrates to owners the effects of the lung disease.