Capnometry in Exotic Animal Species

Key Points

  • Capnometry describes the maximum value of carbon dioxide measured at the end of expiration or end-tidal carbon dioxide (ETCO2).
  • Ventilation status, in the form of ETCO2, should ideally be monitored during general anesthesia.
  • End-tidal carbon dioxide levels correlate fairly well with arterial carbon dioxide (PaCO2) in birds and mammals.
  • Capnography should only be used to measure trends in reptiles as ETCO2 levels can be quite different from PaCO2 due to cardiac shunting of blood past the lungs.
  • Both side-stream and mainstream capnographs can be used in exotic animal patients. Although side-stream units have a reduced effect on mechanical dead space, they are not reliable with small respiratory volumes.
  • Normocapnia in mammals is associated with an ETCO2 of 35-45 mm Hg.
  • Research suggests that an ETCO2 of 30-45 mm Hg is considered appropriate for the anesthetized grey parrot.
  • Hypoventilation and hypercapnia are a potential problem in every species under general anesthesia, however the negative physiologic effects of hypoventilation develop much more rapidly in anesthetized birds. Therefore, assisted ventilation should begin immediately after anesthetic induction in birds to prevent hypercapnia and hypoxemia.
  • This article is part of a series on anesthetic monitoring in exotic animal patients. Additional topics available include:  blood pressure, electrocardiography, pulse oximetry, and monitoring vital signs.

Capnometry measures the maximum value of carbon dioxide (CO2) obtained at the end of expiration or end-tidal carbon dioxide (ETCO2). There is good correlation between ETCO2 and arterial CO2 in birds and mammals and capnography can be used as a reliable tool to evaluate the adequacy of ventilation in these species. Capnography can only be used to identify trends in reptiles because of cardiac shunting of blood past the reptilian lungs . . .

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