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.

Abstract Objective To test whether partial pressure of CO 2 in expired gas (PĒCO 2 ) predicts the partial pressure of CO 2 in arterial blood (PaCO 2 ) in apneic chickens during air sac insufflation anesthesia at three different ventilation states. Secondary objective: To determine the PĒCO 2 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 O 2 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 PĒCO 2 at apnea was recorded. The birds were then paralyzed and gas flow was adjusted to achieve three different PĒCO 2 s 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 PĒCO 2 for 15 minutes, arterial blood gas analysis was performed to determine the PaCO 2 . The chickens were euthanized at the end of the experiment. Results Based on Bland-Altman comparisons, PĒCO 2 was not strongly associated with PaCO 2 during the three ventilation states. The PĒCO 2 at which apnea occurred varied {median (minimum, maximum): 35 (30, 48) mmHg [4.6 (3.9, 6.2) kPa]}. Conclusions Measured PĒCO 2 cannot be used in a simple linear fashion to predict PaCO 2 in birds during air sac insufflation anesthesia. The PĒCO 2 at which apnea occurs during air sac insufflation anesthesia is not predictable. Clinical relevance Arterial blood gases should be used to monitor CO 2 during air sac insufflation anesthesia to verify appropriate patient ventilation.