Introduction

• There are two options for maintenance of equine anesthesia; inhalational anesthesia or total intravenous anesthesia (TIVA)   Anesthesia: intravenous (IV)  .
• Inhalational maintenance requires an anesthetic breathing system   Anesthesia: circuits - overview   a source of oxygen and a suitable volatile agent.
• Minimum Alveolar Concentration (MAC %) is the minimum concentration of volatile agent within the alveoli which prevents 50% of patients reacting with purposeful movement in response to a painful stimulus (skin incision). MAC is used to compare potency. The higher the MAC the less potent the drug. There are several factors which may affect MAC such as age, pregnancy and hypotension.
• The onset of action of an inhalational agent depends on its solubility in the blood. An agent of low solubility such as sevoflurane   Sevoflurane   will have a more rapid onset than halothane   Halothane  .
• Inhalational agents may be used for induction but this method is generally only used for foals.
• Inhalational anesthesia is preferred over intravenous anesthesia    Anesthesia: intravenous (IV)  for horses that are anesthetized for longer than 45 min. 
• The administration of an inhalational agent requires a gas source, eg oxygen, a source of anesthetic agent, an anesthetic machine and a breathing system.

Aims of inhalational anesthesia

Inhalational agents

Toxicity of inhaled agents

Monitoring of anesthetics

Recovery

Further Reading

Publications

Refereed papers

• Recent references from PubMed and VetMedResource.
• Valverde A et al (2010) Comparison of cardiovascular function and quality of recovery in isoflurane-anaesthetised horses administered a constant rate infusion of lidocaine or lidocaine and medetomidine during elective surgery. Equine Vet J 42 (3), 192-199.
• Johnston G M, Eastment J K, Taylor P M & Wood J L N (2004) Is isoflurane safer than halothane in equine anesthesia? Results from a prospective multicenter randomised controlled trial. Equine Vet J 36 (1), 64-71 PubMed.
• Raisis A L et al (2000) A comparison of the hemodynamic effects of isoflurane and halothane anesthesia in horses. Equine Vet J 30, 318-326 PubMed.
• Matthews N S, Hartsfield S M, Mercer D, Beleau M H & MacKenthun A (1998)Recovery from sevoflurane anesthesia in horses: comparison to isoflurane and effect of postmedication with xylazine. Vet Surg 27 (5), 480-485 PubMed.
• Bunsen D B (1990) Use of halothane and isoflurane in the horse. Vet Clin North Am 6 (3), 529-542 PubMed.
• Eicker S W & Cuvelliez S (1990) Equipment for inhalation anesthesia. Vet Clin North Am 6 (3), 543-549 PubMed.
• Steffey E P, Kelly A B & Woliner M J (1978) Time-related responses of spontaneously breathing laterally recumbent horses to prolonged anesthesia with halothane. Am J Vet Res 48 (6), 952-957 PubMed.

Other sources of information

• Taylor P M & Clarke K W (2005) Handbook of Equine Anesthesia. 3rd edn. W B Saunders, UK.
• Johnston G M (2004) Findings from the CEPEF Epidemiological Studies into Equine Perioperative Complications. AAEP Proceedings Vol 50. pp 281-286.
• Thurmon J C, Tranquilli W J, Benson G J (1996) Lumb & Jones' Veterinary Anesthesia. 3rd edn. Williams & Wilkins.
• Steffey E P (1990) Inhalational Anesthesia. In: Current Pract Equine Surg. Eds. White N W & Moore J N. J B Lippincott Company, USA. pp 77-83.
• Hall L W & Clarke K W (1983) Veterinary Anesthesia. 8th edn. Bailliere Tindall, UK.