![]() 70 In isoflurane-anesthetized raptors, a sidestream capnograph provided a relatively good estimation of P aCO 2 for birds weighing more than 400 g and receiving manual positive ventilation with a Bain system. 69 In chickens ventilated using air sac cannulation, ETCO 2 was also not accurate in predicting P aCO 2. In mechanically ventilated pigeons, ETCO 2 overestimated P aCO 2. The accuracy of capnography in birds is variable and related, in part, to the size and type of ventilation. A dropping of the wave to zero can indicate decreased blood flow to the lungs, suggesting a failing heart before arrest. If the wave fails to fall to baseline, it indicates rebreathing of carbon dioxide. The capnograph wave is useful for assessing adequacy of ventilation. This requires no gas sampling but does increase mechanical dead space, and the sensors tend to accumulate water and fail during prolonged usage. The in-line capnographs have a sensor in the breathing system. This causes outside air to be entrained into a nonrebreathing system, causing the values to be lowered. This volume often exceeds the minute ventilation of small patients. This is minimally 300 to 500 mL/min, even in the best of pediatric monitors. The side-stream technique takes a continuous gas sample. The two types of sampling methods are side-stream and in-line ( Figure 19-5). The latter is used to determine appropriate ventilation in the anesthetized patient. The end-tidal carbon dioxide concentration (ETCO 2) is an indirect measure of arterial carbon dioxide concentration (P aCO 2). Darryl Heard, in Current Therapy in Avian Medicine and Surgery, 2016 Capnography
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