Association of partial pressure of carbon dioxide in expired gas and arterial blood at three different ventilation states in apneic chickens (Gallus domesticus) during air sac insufflation anesthesia.

摘要

Objective: To test whether partial pressure of CO₂ in expired gas (PECO₂) predicts the partial pressure of CO₂ in arterial blood (PaCO₂) in apneic chickens during air sac insufflation anesthesia at three different ventilation states. Secondary objective: To determine the PECO₂ at which apnea occurs during air sac insufflation anesthesia. Study design: Randomized cross-over study. Animals: Twenty-three healthy male white leghorn chickens. Methods: Chickens were anesthetized via mask with isoflurane in oxygen and an air sac cannula was placed in the right abdominal air sac. Delivery of isoflurane in O₂ was transferred from the mask to the air sac cannula. The birds were maintained at a surgical plane of anesthesia and apnea was induced by adjusting gas flow; the PECO₂ at apnea was recorded. The birds were then paralyzed and gas flow was adjusted to achieve three different PECO₂s in random order: 43 mmHg (5.6 kPa) [hypoventilation]; 33 mmHg (4.3 kPa) [normoventilation]; and 23 mmHg (3.0 kPa) [hyperventilation]. After maintaining the target expired isoflurane concentration (EIso; 1.85 or 1.90%) and PECO₂ for 15 minutes, arterial blood gas analysis was performed to determine the PaCO₂. The chickens were euthanized at the end of the experiment. Results: Based on Bland-Altman comparisons, PECO₂ was not strongly associated with PaCO₂ during the three ventilation states. The PECO₂ at which apnea occurred varied {median (minimum, maximum): 35 (30, 48) mmHg [4.6 (3.9, 6.2) kPa]}. Conclusions: Measured PECO₂ cannot be used in a simple linear fashion to predict PaCO₂ in birds during air sac insufflation anesthesia. The PECO₂ at which apnea occurs during air sac insufflation anesthesia is not predictable. Clinical relevance: Arterial blood gases should be used to monitor CO₂ during air sac insufflation anesthesia to verify appropriate patient ventilation.