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CLINICAL TECHNIQUES
Cyndi Brown, DVM, Column Editor
Air sac cannula placement in birds
Cyndi Brown, DVM1 & Anthony A. Pilny, DVM, ABVP (Avian)2
Air sac cannulas are indicated in birds with upper respiratory obstruction or for ventilation during surgical procedures involving the head and neck. Proper technique, knowledge of potential complications, and an understanding of the indications for air sac tube placement are important for scientists, veterinarians, and technicians who work with birds.
The lungs of birds are small, compact, spongy structures within the chest cavity that are fitted closely against the contours of the ribs on either side of the spine. Avian lungs weigh as much as the lungs of mammals of similar body weight, but because avian lungs have much greater tissue density, they occupy about one-half the volume 1.
The air sac system is a vital part of the avian respiratory system. Air sacs are thin-walled structures, one to two cell layers thick, that extend throughout the body cavity and into the wing and leg bones2. Most birds have nine air sacs: two cervical, two cranial thoracic, two caudal thoracic, two abdominal, and a single interclavicular air sac2. The abdominal air sacs carry air to leg and pelvic bones; the interclavicular sac branches into the wing bones, sternum, and syrinx.
The air sacs connect directly to the bronchi and make possible an effective continuous flow of air through the lungs1. Air flows into the avian lungs through a set of bronchi into the air-capillary system, which is the primary site of O2 and CO2 exchange.
There is a constant flow of air through the
avian lung, allowing a more efficient extraction of oxygen than occurs in the mammalian lung. Half of the inhaled air during the first inhalation in this cycle passes through the primary bronchi to the posterior air sacs.During the exhalation of the first breath, the inhaled air moves from the posterior air sacs into the lungs, where it flows through the gas-exchange areas. The next time the bird inhales, this O2-depleted air moves into the anterior air sacs. During the second exhalation, the CO2-rich air is then expelled from the anterior air sacs, bronchi, and trachea back into the atmosphere. The constant airflow through the avian lung allows...