Anesthetic Depth in Exotic Animals: Monitoring the Degree of Central Nervous System Depression

Key Points

  • Anesthetic depth is the degree to which the central nervous system is depressed by a general anesthetic agent.
  • Exercise caution when evaluating anesthetic depth in exotic animal patients, particularly when monitoring a novel species, as response to anesthetic agents can defy generalization in any given individual, particularly when anesthesia is achieved using a combination of drugs.
  • As a general rule of thumb, as anesthetic depth increases, muscle tone decreases and the respiratory pattern may become regular and even.
  • Respiratory rate and depth are important guides to anesthetic depth in birds and mammals, but respiration is a poor indicator in reptiles since apnea is often observed at a surgical plane of anesthesia.
  • As anesthetic depth increases, reflexes become attenuated. At a surgical plane of anesthesia, pedal withdrawal reflexes are often absent and the corneal reflex is present but sluggish in those patients possessing eyelids.
  • Although the palpebral reflex is often lost at a surgical plane of anesthesia in reptiles possessing eyelids and birds, this reflex may not be lost until dangerously deep levels of anesthesia in many mammals.
  • Excessive anesthetic depth is associated with severe, life-threatening cardiovascular depression manifested by bradycardia, hypotension, and hypercapnia. This stage can also be recognized by the loss of all reflexes, including corneal and palpebral. Death will ensue if the patient’s status is left unchecked.
  • The anesthetist must remain vigilant for any changes in patient status during the perianesthetic period. Changes in anesthetic depth can occur particularly quickly in birds.
  • This article is part of a RACE-approved Anesthetic Monitoring teaching module. Visit the articles on physiologic monitoring of vital signs, blood pressure, capnometry, pulse oximetry, and electrocardiography for additional information in exotic animal patients.
  • The content presented here is also available as an approximately 23-minute slideshow recording. More detailed information is available in the article version of this content, however it is not necessary to read the article to complete the teaching module quiz.

A dedicated anesthetist should be assigned to monitor every patient during the perianesthetic period. The anesthetist is fundamental to patient safety because she assures the patient is not aware, not moving, and not in pain, all while maintaining stable anesthetic depth. A deep plane of anesthesia can lead to hypoventilation and hypoxemia, reduced cardiac output, hypotension, inadequate tissue perfusion, central nervous system (CNS) depression, and prolonged recovery. This review article first explores the stages of anesthesia and then discusses assessment of anesthetic depth in exotic companion mammals, birds, and reptiles . . .


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Further reading

Diven K. Inhalation anesthetics in rodents. Lab Anim (NY) 32(3): 44–47, 2003. DOI: 10.1038/laban0303-44..

Imai A, Steffey EP, Farver TB, Ilkiw JE. Assessment of isoflurane-induced anesthesia in ferrets and rats. Am J Vet Res 60(12):1577-1583, 1999.

Imai A, Steffey EP, Ilkiw JE. Comparison of clinical signs and hemodynamic variables used to monitor rabbits during halothane- and isoflurane-induced anesthesia. Am J Vet Res 60(10):1189-1195, 1999.

Korbel R. Vergleichende Untersuchungen zur Inhalationsanästhesie mit Isofluran (Forene) und Sevofluran (Sevorane) bei Haustauben (Columba livia Gmel., 1789, var. dom.) und Vorstellung eines Referenz-Narkoseschemas für Vögel. Tierärztl Prax 26:71-83, 1998.

Read MR. Evaluation of the use of anesthesia and analgesia in reptiles. J Am Vet Med Assoc 224(4):547-552, 2004. DOI: 10.2460/javma.2004.224.547..

Sandmeier P. Evaluation of medetomidine for short-term immobilization of domestic pigeons (Columba livia) and Amazon parrots (Amazona species). J Avian Med Surg 14(1):8-14, 2000.

Schumacher J, Mans C. Anesthesia. In: Mader DR (ed). Current Therapy in Reptile Medicine and Surgery, 3rd ed. St. Louis: Elsevier; 2014: 308.

To cite this page:

Pollock CG, Nugent-Deal J. Anesthetic depth in exotic animals: monitoring the degree of central nervous system depression. Aug 29, 2020. LafeberVet Web site. Available at  https://lafeber.com/vet/anesthetic-depth-in-exotic-animals-monitoring-the-degree-of-central-nervous-system-depression/