Veterinarians familiar with capnography have frequently encountered technical difficulties associated with the use of older or less expensive capnometers, especially when sampling respiratory gas from relatively small, spontaneously breathing, anesthetized animals that frequently demonstrate altered patterns of breathing. Volumetric capnography simultaneously measures expired CO2 and tidal volume, facilitating the identification of CO2 from three sequential compartments: apparatus (anesthetic equipment), anatomic deadspace, and progressively emptying alveoli (alveolar gas). Although mammalian respiratory anatomy and function are remarkably similar among species, there are obvious allometric differences. Capnography in animals such as rodents and birds, nevertheless, remains challenging. A wide range of respiratory volumes exists among animal species. There is remarkable similarity in arterial blood pH and gas values. Capnometry is more commonly used to monitor ventilation in anesthetized horses. Capnography has also been used to evaluate pulmonary function in awake dolphins.