How to Maximize Standing Chemical Restraint

HOW-TO SESSION: FIELD ANESTHESIA AND PAIN MANAGEMENT

Alonso Guedes, DVM, MS, PhD

1. Introduction used for short procedures (Ͻ30 minutes), whereas Sedation and analgesia are commonly required to multiple boluses (ie, as needed) or a constant rate help facilitate diagnostic and treatment procedures infusion (CRI) may be necessary for longer proce- ␣ dures. For longer procedures, a loading dose fol- in standing horses. 2-Adrenergic receptor (AR) agonists alone or in combination with opioids are lowed by a CRI is probably best because it produces used most commonly for this purpose.1 Although more constant plasma levels and hence more stable such drug combinations in standing sedation are sedation levels, and the overall dose used may be useful and mitigate some of the risks associated lower than with multiple doses. Administering with general anesthesia,2 they are not free of ad- small additional boluses can be used to intensify the ␣ verse effects. Dose-dependent respiratory depres- level of sedation if required. Whereas 2-AR ago- sion, hypertension, bradyarrhythmias, decreases in nists are generally considered potent and useful sed- ␣ cardiac output, hyperglycemia, polyuria, and de- atives, some horses sedated with 2-AR agonists creased gastrointestinal motility are commonly may suddenly react to stimulation (even to touch), ␣ 3–8 caused by 2-AR agonists. Also, the presence of may become excited, or may develop aggression (es- fear, stress, excitement, and pain can lead to failure pecially with xylazine). Opioids can be used to ␣ to achieve satisfactory sedation with 2-AR ago- modify some of these responses and improve the nists.3,5 The goal of this report is to present a prac- quality of the chemical restraint. tical technique that can help equine veterinarians in Combining opioids (morphine, butorphanol) with ␣ maximizing standing chemical restraint in patients 2-AR agonists will produce a state referred to as undergoing diagnostic and/or surgical procedures. neuroleptanalgesia, in which the level of sedation and analgesia is more profound and greatly im- 2. Drugs and Drug Administration Techniques proves the chemical restraint. The opioids can be Xylazine, detomidine, and romiﬁdine are the most used as a single bolus for short procedures or, for ␣ common 2-AR agonists used to produce standing longer procedures, as multiple intermittent boluses chemical restraint in equines, and the intravenous or as a loading dose followed by a CRI. Combina- (IV) route of administration is preferred in most tions of detomidine and morphine are very useful for cases. An intravenous catheter is very useful for procedures expected to be associated with strong drug and ﬂuid administration, especially for longer noxious stimulation such as (but not limited to) procedures. A single bolus administration can be ovariectomy and tooth extraction. For this tech-

NOTES

AAEP PROCEEDINGS ր Vol. 59 ր 2013 461 HOW-TO SESSION: FIELD ANESTHESIA AND PAIN MANAGEMENT nique, the horse is first sedated with detomidine benefit from a sling. Drugs and materials should (0.005–0.01 mg/kg IV) and then given a slow (ϳ5- be available to induce and maintain general anes- minute) bolus of morphine (0.03–0.05 mg/kg IV). thesia in the case that a patient undergoing stand- Morphine should be administered slowly to reduce ing chemical restraint becomes recumbent. For possible risks of histamine release and to allow for long procedures, a urinary catheter should be placed in ␣ early detection of an excitatory reaction. A CRI of equine patients sedated with 2-AR agonists because both drugs can then be instituted (detomidine at these drugs increase urine production. 0.005–0.01 mg/kg per hour and morphine at 0.03– 0.05 mg/kg per hour). Alternatively, morphine can 3. Discussion be administered as intermittent IV boluses (slowly) Horses sedated with detomidine and morphine are as needed throughout the procedure. During the typically less responsive to noxious as well as non- CRI, sedation level can be deepened with additional noxious stimulation. However, local blocks are still IV boluses of detomidine (0.002–0.005 mg/kg) or required to facilitate most surgical procedures. xylazine (0.1–0.2 mg/kg) as needed. Butorphanol When given as a CRI, this combination produces can be used instead of morphine to improve sedation stable sedation that can be relatively easily adjusted and analgesia produced by detomidine. It is ad- as needed. In our institution, this is the preferred ministered as an initial IV bolus (loading dose) of method of sedation of horses undergoing urogenital 0.01–0.02 mg/kg that can be followed by a CRI as well as head procedures. (0.01–0.02 mg/kg per hour) or intermittent IV bo- We have observed that significantly more de- luses (0.01–0.02 mg/kg IV) as needed. For the tomidine and morphine is required to produce sat- CRI, the drugs are best delivered with the use of isfactory chemical restraint in horses undergoing syringe pumps as it allows for the most accurate extensive dental procedures (ie, root canals, multi- dosing. However, drugs can also be added to a bag ple dental extractions, etc). Some of these horses of crystalloid fluids and delivered through gravity may have significant bradycardia and require treat- flow with a drip set. For maximal control of infu- ment with an anticholinergic such as butylscopol- sion rates, drugs should be given through separate amine.a It can be given as small doses (0.05–0.1 syringe pumps or fluid bags. For example, 10 mg mg/kg IV) as needed to maintain heart rate within of detomidine can be added to a 250-mL bag of an acceptable range for the patient. saline (0.04 mg/mL) and dripped to effect through Horses sedated with detomidine and morphine, a 60-drop/mL drip set. With this setup, 1 drop especially those undergoing prolonged procedures, per second will deliver 60 mL of fluid per hour or will also receive a crystalloid solution such as lac- 2.4 mg of detomidine per hour. This is the equiva- tated Ringer’s solution (2–5 mL/kg per hour) to lent to a dose of 0.005 mg/kg per hour of detomidine. maintain fluid balance and replace losses caused by It can be easily adjusted up or down from here as polyuria. These horses also typically receive min- needed. eral oil through a nasogastric tube at the end of In patients undergoing urogenital procedures the procedure and are kept on colic watch for the (ie, ovariectomy, removal of kidney stones), caudal following 24 hours. Morphine is avoided, used at epidural (S5-Cox1 or Cox1-Cox2) administration of the lowest possible doses, or replaced with butorpha- morphine (0.1 mg/kg diluted into 15–20 mL of sa- nol in horses with a recent history of colic. Antag- line) produces useful analgesia during and after onism of detomidine or morphine is typically not surgery.9 Although not typically used for sedation needed but could be performed with the appropriate of adult horses, very low doses of midazolam or antagonists. diazepam (0.005–0.01 mg/kg) appear to relax the 3 tongue and jaw and facilitate dental procedures. References and Footnote Patients undergoing dental procedures may benefit 1. Hubbell JA, Saville WJ, Bednarski RM. The use of seda- from attenuation of visual (apply blindfold), audi- tives, analgesic and anaesthetic drugs in the horse: an elec- tory (apply cotton in ears), and oral tactile sensation tronic survey of members of the American Association of (apply lidocaine gel on the surface of the tongue and Equine Practitioners (AAEP). Equine Vet J 2010;42:487– oral mucosa). Patients with severe dental disease 493. 2. Johnston GM, Eastment JK, Wood JLN, et al. The confiden- and suspected pathologic pain (ie, hyperalgesia, al- tial enquiry into perioperative equine fatalities (CEPEF): lodynia) may react severely to needle placement mortality results of phases 1 and 2. Vet Anaesth Analg 2002; through the skin during the performance of nerve 29:159–170. blocks. Application of a thick layer of eutectic mix- 3. Ringer SK. Chemical restraint for standing surgery. In: Equine Surgery. 4th edition. St Louis: WB Saunders; ture of local anesthetics (EMLA) cream on the skin 2012:253–262. over the site of the nerve block 20 to 30 minutes 4. Dyson DH, Pascoe PJ, Viel L, et al. Comparison of detomi- before the procedure greatly facilitates the perfor- dine hydrochloride, xylazine, and xylazine plus morphine in mance of the nerve block. Patients undergoing pro- horses: a double blind study. J Equine Vet Sci 1987;7:211– 215. longed sedation or expected to require deep sedation 5. Jochle W, Woods GL, Little TV, et al. Detomidine hydro- levels are in greater danger of development of sig- chloride versus xylazine plus morphine as sedative and an- nificant ataxia and recumbency and therefore will algesic agents for flank laparotomies and ovary and oviduct

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removal in standing mares. J Equine Vet Sci 1991;11:225– medetomidine and morphine for sedation during standing 228. laparoscopy in horses. Equine Vet J 2009;41:153–159. 6. Kamerling SG, Cravens WM, Bagwell CA. Objective assess- 9. Van Hoogmoed LM, Galuppo LD. Laparoscopic ovariectomy ment of detomidine-induced analgesia and sedation in the using the endo-GIA stapling device and endo-catch pouches horse. Eur J Pharmacol 1988;151:1–8. and evaluation of analgesic efﬁcacy of epidural morphine 7. Wilson DV, Bohart GV, Evans AT, et al. Retrospective anal- sulfate in 10 mares. Vet Surg 2005;34:646–650. ysis of detomidine infusion for standing chemical restraint in 51 horses. Vet Anaesth Analg 2002;29:54–57. 8. Solano AM, Valverde A, Desrochers A, et al. Behavioural aBuscopan௡, Boehringer Ingelheim Vetmedica, St. Joseph, MO and cardiorespiratory effects of a constant rate infusion of 64506.

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