Anesthesia in horses is often associated with complications, including postoperative myopathies and colic, that contribute to the relatively high mortality rate in this species.1 The relevance of peripheral tissue perfusion and its association with these problems has gained increasing attention during the past few years. However, detailed information about the impact of various anesthetics on tissue perfusion is limited.
Horses are commonly anesthetized with volatile anesthetic agents for prolonged surgery. The very low blood-gas partition coefficient of desflurane2 (0.45) offers the potential for more precise control of anesthetic depth and more rapid recovery, compared with effects for other inhalation anesthetics.3 These properties make desflurane desirable for use in horses because rapid recovery is crucial in equine anesthesia. Like most volatile anesthetic agents, desflurane causes dose-related cardiopulmonary depression,4 which contributes to the high mortality rate associated with equine anesthesia.1 Therefore, it is preferable to minimize the amount of inhalation agent used by providing analgesia and muscle relaxation through other sources. Various α2-adrenoceptor agonists have been used in balanced anesthetic protocols that provide sedation and analgesia, which reduces the MAC of volatile anesthetic agents and improves the quality of recovery.5
Propofol is unsatisfactory as the sole agent for anesthesia of equids; the volume of drug required is too large to enable sufficiently rapid injection, and the quality of anesthetic induction is unpredictable. However, propofol results in a good quality of anesthetic induction after patients are sedated with α2-adrenoceptor agonists.6 A total intravenous anesthesia protocol that involved the use of medetomidine and propofol maintained good cardiovascular function in ponies that were anesthetized for ≥ 4 hours, and there was good recovery quality.7
Dexmedetomidine is a highly selective α2-adrenoceptor agonist that causes sedation, anxiolysis, and analgesia. Cardiopulmonary effects and pharmacokinetics of dexmedetomidine have been evaluated in ponies after IV administration. Although the cardiopulmonary effects are similar to those reported for other α2-adrenoceptor agonists, it has been determined that dexmedetomidine is rapidly redistributed and has short-acting effects in horses.8 These characteristics make it ideal for use in partial intravenous anesthesia protocols. A dexmedetomidine CRI of 1.75 μg•kg−1•h−1 significantly reduces the MAC of sevoflurane in ponies by 53%.9
Peripheral perfusion is also impaired during anesthesia, which can lead to a reduction of peripheral oxygenation. Postanesthetic myopathy, caused by impaired perfusion and oxygenation during anesthesia, is a recognized complication of equine anesthesia that has been identified as one of the principal causes of perioperative death in anesthetized horses.1 Although volatile anesthetics can impair muscle perfusion as well as intestinal perfusion,10,11 propofol has been found to improve peripheral perfusion in humans.12,13 One explanation for this phenomenon is that the anesthesia-induced vasodilatation in those studies12,13 might predominantly have involved small tissue venules when propofol was used.
The purpose of the study reported here was to determine global and peripheral perfusion and oxygenation during anesthesia with desflurane and propofol combined with a CRI of dexmedetomidine in horses. We hypothesized that the CRI of dexmedetomidine would reduce anesthetic requirements and that cardiovascular variables as well as peripheral perfusion and oxygenation would be maintained equally well during anesthesia with desflurane and propofol.
This manuscript represents a portion of a thesis submitted by Dr. Neudeck to the Clinic for Horses, University of Veterinary Medicine Hannover, Foundation, Hannover, Germany, as partial fulfillment of the requirements for a Doctor medicinae veterinariae degree.
Presented in abstract form at the Association of Veterinary Anaesthetists Spring Meeting, Lyon, France, April 2016.
Constant rate infusion
Fraction of inspired oxygen
Minimal alveolar concentration
Mean arterial blood pressure
Minimal infusion rate
Alveolar partial pressure of carbon dioxide
Alveolar-arterial difference in partial pressure of oxygen
End-expiratory partial pressure of carbon dioxide
Partial pressure of water vapor
Systemic vascular resistance
Dexdomitor, 0.5 mg/mL, Orion Pharma, Espoo, Finland.
Propofol 2%, 20 mg/mL, Fresenius Kabi, Langenhagen, Germany.
Suprane, Baxter Deutschland GmbH, Höchstadt, Germany.
Grass stimulator S48, Grass Instrument Company, Quincy, Mass.
Ambu neuroline 70005-K/12, Ambu GmbH, Bad Nauheim, Germany.
O2C Oxygen to See device, LEA Medizintechnik, Gießen, Germany.
LF-2, LEA Medizintechnik, Gießen, Germany.
LF-17, LEA Medizintechnik, Gießen, Germany.
GE Datex-Ohmeda S/5 compact anesthesia monitor, GE Healthcare, München, Germany.
Quick Cal calibration gas, GE Healthcare Finland OY, Helsinki, Finland.
SAS, version 9.3, SAS Institute Inc, Cary, NC.
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