What does end-tidal CO2 monitoring during anesthesia provide in small animals?

• A. An invasive measurement of arterial CO2
• B. A noninvasive measure of ventilation adequacy
• C. An assessment of cardiac output
• D. An indicator of oxygen saturation

Answer: (B)

End-tidal CO2 monitoring during anesthesia provides a noninvasive measure of ventilation adequacy in small animals. Capnography analyzes CO2 in the exhaled breath, and the end-tidal value reflects the CO2 concentration at the end of expiration when alveolar gas is released. This gives real-time insight into how well the animal is ventilating: rising values suggest hypoventilation or increased CO2 production, while dropping values point to hyperventilation, reduced CO2 production, or excessive dead space. The waveform also helps detect problems like apnea, airway obstruction, circuit leaks, or rebreathing. It is noninvasive and widely used because arterial CO2 measurement requires blood sampling, and oxygen saturation is assessed by other means (like pulse oximetry). While ETCO2 often correlates with arterial CO2 under stable conditions, it is not a direct arterial measurement and can be affected by ventilation-perfusion changes.