In the past 10 to 20 years, anesthetic management of horses undergoing surgery has improved greatly, particularly with regard to the monitoring of arterial blood pressure, treatment of hypotension, prevention of post-anesthetic myopathy, and provision of assisted ventilation. However, recovery from anesthesia still entails risk for both horses and personnel.
Traditionally, induction of anesthesia in horses has been performed by use of drugs administered IV, such as xylazine, guaifenesin or diazepam (or both), and ketamine; however, for maintenance of anesthesia for procedures > 60 minutes in duration, inhalation anesthetic agents such as isoflurane and sevoflurane are recommended.1 An advantage of maintenance with contemporary inhalation anesthetic agents is that they are eliminated from the body mainly through the respiratory tract and do not accumulate during long surgeries or require extensive metabolism for the termination of their effects. However, in horses, the recovery from inhalation anesthesia is often less than ideal and, occasionally, a poor recovery results in serious injuries. Reportedly, 0.2% to 1.6% of recoveries of horses from inhalation anesthesia result in serious or life-ending injuries, such as fractures.2–4 Although these data illustrate the severe consequences of a poor recovery from anesthesia in a few horses, they do not reflect the overall morbidity among horses during recovery in terms of nonterminal injuries such as lacerations, breakdown of surgical incisions, or destruction of bandages and do not account for the time spent by, or injuries incurred by, personnel who attempt to assist these horses.
One study5 conducted to compare sevoflurane and isoflurane anesthesia in horses revealed that sevoflurane resulted in faster and better quality recoveries, compared with recoveries from isoflurane anesthesia, but a more recent report6 indicated no difference in duration or quality of recovery from anesthesia. In recent years, there has been increasing interest in the use of injectable anesthetic agents, such as xylazine, ketamine, propofol, and guaifenesin, for maintenance of anesthesia in horses partly because of reports7,8 published during the 1990s that suggested superior quality of recoveries when injectable drugs were used for maintenance of anesthesia. In 1 study,9 the quality of recovery from anesthesia was considered excellent or good in 35 of 36 (97%) horses in which anesthesia was maintained for 1 hour by use of xylazine-ketamine infusions. However, because of possible prolonged or difficult recoveries associated with excessive accumulation of injectable drugs and the time required for drug metabolism, long-term maintenance of anesthesia with currently available injectable drugs is still not generally recommended.1
To promote improved recoveries following long anesthesia procedures, attempts have been made to combine the advantages of injectable and inhalation anesthetic agents. It was speculated that administration of injectable anesthetic agents for induction and inhalation anesthetic agents for maintenance, followed by administration of injectable drugs at the end of anesthesia could result in an improved quality of recovery from anesthesia. Investigators in 1 study10 evaluated the use of xylazine-ketamine infusions to modify recoveries from isoflurane anesthesia in horses, but only the duration of recovery, not the quality, was increased by a significant margin. Despite the failure of the combination of xylazine and ketamine to result in a clear improvement in recovery from isoflurane anesthesia in horses, the effect of a similar xylazine-ketamine infusion after sevoflurane anesthesia still warrants investigation. In addition, propofol, an injectable anesthetic agent that is associated with rapid, smooth recovery in several species, has been used for both induction and maintenance of anesthesia in horses.8,11–13 In horses, the use of the combination of xylazine and propofol to modify recovery from desflurane anesthesia has been reported to result in an improved quality of recovery but potentially detrimental respiratory depression.14,15
The primary hypothesis for the study reported here was that prolongation of sedation and recumbency by use of a xylazine-ketamine or xylazine-propofol infusion administered during the first 15 to 30 minutes after discontinuation of sevoflurane inhalation would result in an improved quality of recovery from anesthesia in horses, compared with the quality of recovery from sevoflurane anesthesia alone. It was also hypothesized that cardiopulmonary variables in horses would not be negatively impacted by the use of a xylazine-ketamine or xylazine-propofol infusion to modify recovery from sevoflurane anesthesia.
Mean arterial blood pressure
End-tidal partial pressure of carbon dioxide
Escort II, MDE, Arleta, Calif.
Cobe pressure transducer, Electricom, Denver, Colo.
ABL505, Radiometer Medical A/S, Copenhagen, Denmark.
Biochem 8100, Biochem International Inc, Waukesha, Wis.
Scott Medical Products, Plumsteadville, Pa.
. PROC MIXED, SAS, version 6.11, SAS Institute Inc, Cary, NC.
Mama KR, Department of Clinical Sciences, College of Veterinary Medicine and Biomedical Sciences, Colorado State University, Fort Collins, Colorado: Unpublished data, 2005.
Martinez EA, Wagner AE, Driessen B, et al. Guidelines for anesthesia in horses. American College of Veterinary Anesthesiologists. Available at: www.acva.org/docs/Equine. Accessed Nov 28, 2010.
Hodgson DS, Dunlop CI. General anesthesia for horses with specific problems. Vet Clin North Am Equine Pract 1990; 6:625–650.
Young SS, Taylor PM. Factors influencing the outcome of equine anaesthesia: a review of 1,314 cases. Equine Vet J 1993; 25:147–151.
Johnston GM, Taylor PM, Holmes MA, et al. Confidential enquiry into perioperative equine fatalities (CEPEF-1): interim results of the United Kingdom study, in Proceedings. 41st Annu Meet Am Assoc Equine Pract 1995;192–193.
Matthews NS, Hartsfield SM, Mercer D, et al. Recovery from sevoflurane anesthesia in horses: comparison to isoflurane and effect of postmedication with xylazine. Vet Surg 1998; 27:480–485.
Leece EA, Corletto F, Brearley JC. A comparison of recovery times and characteristics with sevoflurane and isoflurane anaesthesia in horses undergoing magnetic resonance imaging. Vet Anaesth Analg 2008; 35:383–391.
Young LE, Bartram DH, Diamond MJ, et al. Clinical evaluation of an infusion of xylazine, guaifenesin, and ketamine for maintenance of anaesthesia in horses. Equine Vet J 1993; 25:115–119.
Mama KR, Pascoe PJ, Steffey EP, et al. Comparison of two techniques for total intravenous anesthesia in horses. Am J Vet Res 1998; 59:1292–1298.
Mama KR, Wagner AE, Steffey EP, et al. Evaluation of xylazine and ketamine for total intravenous anesthesia in horses. Am J Vet Res 2005; 66:1002–1007.
Wagner AE, Mama KR, Steffey EP, et al. A comparison of equine recovery characteristics after isoflurane or isoflurane followed by a xylazine-ketamine infusion. Vet Anaesth Analg 2008; 35:154–160.
Mama KR, Steffey EP, Pascoe PJ. Evaluation of propofol for general anesthesia in premedicated horses. Am J Vet Res 1996; 57:512–516.
Bettschart-Wolfensberger R, Freeman S, Bettschart RW, et al. Assessment of a medetomidine/propofol total intravenous anaesthesia, (TIVA) for clinical anaesthesia in equidae. Pferdeheilkunde 2002; 18:39–48.
Muir WW, Lerche P & Erichson D. Anaesthetic and cardiorespiratory effects of propofol at 10% for induction and 1% for maintenance of anaesthesia in horses. Equine Vet J 2009; 41:578–585.
Steffey EP, Mama KR, Brosnan RJ, et al. Effect of administration of propofol and xylazine hydrochloride on recovery of horses after four hours of anesthesia with desflurane. Am J Vet Res 2009; 70:956–963.
Steffey EP, Brosnan RJ, Galuppo LD, et al. Use of propofol-xylazine and the Anderson sling suspension system for recovery of horses from desflurane anesthesia. Vet Surg 2009; 38:927–933.
Steffey EP, Mama KR, Galey FD, et al. Effects of sevoflurane dose and mode of ventilation on cardiopulmonary function and blood biochemical variables in horses. Am J Vet Res 2005; 66:606–614.
Bergadano A, Lauber R, Zbinden A, et al. Blood/gas partition coefficients of halothane, isoflurane and sevoflurane in horse blood. Br J Anaesth 2003; 91:276–278.
Wagner AE, Bednarski RM, Muir WW III. Hemodynamic effects of carbon dioxide during intermittent positive pressure ventilation in horses. Am J Vet Res 1990; 51:1922–1929.
Khanna AK, McDonell WN, Dyson DH, et al. Cardiopulmonary effects of hypercapnia during controlled intermittent positive pressure ventilation in the horse. Can J Vet Res 1995; 59:213–221.
Wagner AE, Muir WW III, Hinchcliff KW. Cardiovascular effects of xylazine and detomidine in horses. Am J Vet Res 1991; 52:651–657.