Avian Anatomy and Physiology

When considering anesthetic procedures for avian patients, it is critical to be aware of their unique respiratory and circulatory physiology. The avian respiratory system is different from mammals in that it has separate ventilatory and gas exchange compartments, making it highly efficient compared with other vertebrates. This compartment includes the major airways, an air sac system, and the thoracic skeleton with its associated muscles. The parabronchial lungs are the primary tissues for gas exchange. Avian lungs are relatively smaller compared with mammalian and the parabronchi are nonexpandable. The cardiovascular system also exhibits significant adaptations to the high metabolic demands necessary for flight. Heat is lost via radiation, evaporation, convection, and conduction. The normal body temperatures of most caged birds range from 39 to 43°C. Since many birds are small and have a high body-to-surface area ratio they radiate heat rapidly.