• Monique Paré, John W Ludders, and Hollis N Erb.
• Department of Clinical Sciences, College of Veterinary Medicine, Cornell University, Ithaca, New York 14853, USA. mdp86@cornell.edu
• Vet Anaesth Analg. 2013 May 1; 40 (3): 245-56.

ObjectiveTo test whether partial pressure of CO2 in expired gas (PĒCO2) predicts the partial pressure of CO2 in arterial blood (PaCO2) in apneic chickens during air sac insufflation anesthesia at three different ventilation states.Secondary ObjectiveTo determine the PĒCO2 at which apnea occurs during air sac insufflation anesthesia.Study DesignRandomized cross-over study.AnimalsTwenty-three healthy male white leghorn chickens.MethodsChickens 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 PĒCO2 at apnea was recorded. The birds were then paralyzed and gas flow was adjusted to achieve three different PĒCO2 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 PĒCO2 for 15 minutes, arterial blood gas analysis was performed to determine the PaCO2 . The chickens were euthanized at the end of the experiment.ResultsBased on Bland-Altman comparisons, PĒCO2 was not strongly associated with PaCO2 during the three ventilation states. The PĒCO2 at which apnea occurred varied {median (minimum, maximum): 35 (30, 48) mmHg [4.6 (3.9, 6.2) kPa]}.ConclusionsMeasured PĒCO2 cannot be used in a simple linear fashion to predict PaCO2 in birds during air sac insufflation anesthesia. The PĒCO2 at which apnea occurs during air sac insufflation anesthesia is not predictable.Clinical RelevanceArterial blood gases should be used to monitor CO2 during air sac insufflation anesthesia to verify appropriate patient ventilation.© 2013 The Authors. Veterinary Anaesthesia and Analgesia © 2013 Association of Veterinary Anaesthetists and the American College of Veterinary Anesthesia and Analgesia.

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