HOW TO PERFORM FIELD ANESTHESIA AND PAIN MANAGEMENT


Table 1. Dose of Drugs Frequently Used for Standing Chemical Restraint Drug


Intravenous Dose Acepromazine


Midazolam or diazepam9


Xylazine15 Detomidine12 Romifidine9 Dexmedetomidine20 Butorphanol9


Buprenorphine Morphine Meperidine Ketamine9 Lidocaine20


0.02–0.05 mg/kg


0.02 mg/kg Infusion rate: 0.06 mg/kg/hr


0.5–1.0 mg/kg Infusion rate: 0.6–0.8 mg/kg/hr


0.01–0.02 mg/kg Infusion rate: 0.01–0.02 mg/kg/hr after initial bolus


0.04–0.120 mg/kg Infusion rate: 0.03 mg/kg/hr


0.003–0.007 mg/kg Infusion rate: 0.004–0.006 mg/kg/hr


0.01–0.03 mg/kg Infusion rate: 0.04 mg/kg/hr 0.006–0.01 mg/kg


0.1–0.4 mg/kg 0.2–0.8 mg/kg


0.2–0.4 mg/kg Infusion rate: 1.2 mg/kg/hr. Infusion rate: 2.4–3.6 mg/kg/hr


Comments


Use cautiously in stressed or hypotensive horses. Usually used in low doses in combination with other drugs. Does not produce analgesia.


Reduces tongue movement and chewing when performing dental procedures. Does not produce analgesia or sedation. Does cause weakness and ataxia.


Ataxia produced, head-down posture. Start with low dose and repeat as needed or use an infusion.


Ataxia produced, head-down posture. Start with low dose. Use an infusion for prolonged procedures.


Reduced ataxia, reduced analgesia compared to other 2 agonists.


Short duration. Not approved for horses in United States. Expensive


Potential for excitement. Usually used in combination with a sedative or tranquilizer.


Potential for excitement. Usually used in combination with a sedative or tranquilizer.


Potential for excitement. Sedate with xylazine or detomidine prior to administering morphine. Reversible with naloxone.


Potential for excitement. Sedate with xylazine or detomidine prior to administering morphine. Reversible with naloxone.


Used in combination. Little to no sedative effect. May augment analgesia of 2


agonists. Potential for hypotension and ataxia.


from 0.4 to 1.2 mg/kg/hr given at a constant rate. The effectiveness of the technique seems to depend on the type of pain being induced or treated with excellent results seen for patients with burns and some utility in dental procedures.


Lidocaine


Lidocaine infusions provide anti-nociception to elec- tric stimuli without producing significant sedation in conscious horses, but its effects on visceral pain are unproven.20,21 Infusions are usually well toler- ated, but bolus administration may be associated with hypotension and ataxia.


3. Approach to Maximal Standing Chemical Restraint


Maximal standing chemical restraint is approached de novo in some patients but is frequently performed as an “add on” when the initial sedative drug or drug combination is ineffective. Initially, an assessment should be made with regard to why the initial ad- ministration was ineffective. Were the correct drugs at the usual doses administered? If the drugs were intended for IV use, where they admin- istered IV? Was sufficient time allowed for the drugs to take maximal effect before the procedure was begun? Was the environment conducive to the production of a sedated state? Was the analgesia produced sufficient for the intended procedure? Is there something about this horse that was under- estimated or misinterpreted? Frequently, when an attempt at standing chemical restraint has failed,


some combination of these potential problems may have occurred. The veterinarian must make a de- termination whether to continue with the current program or postpone the procedure until a later date. If the decision is to continue, the veterinarian should determine the length of time from the initial administration of sedative to the present. As an example, the duration of action of IV xylazine is approximately 30 minutes. If you are outside of this window, you are essentially starting over. If the initial drug was detomidine or romifidine, your window is approximately 45 to 60 minutes. If the horse was somewhat sedate after the initial administration of drug but not to a point where the procedure could be performed, the author recom- mends the following general protocol: Readminis- ter the initial dose of your preferred drug or drug combination and establish venous access with a catheter. The placement of a catheter is important because it reduces the stimulation of multiple needle sticks and assures drug delivery into the vascular space. Dilute detomidine (10 mg) or xylazine (1000 mg) in normal saline (250 or 500 mL) and infuse 25% of the volume at a fast drip rate. If the desired level of sedation is attained, slow the drip rate and per- form the procedure. If the level of sedation be- comes inadequate, administer an additional 25% of the volume at a fast rate, then slow the rate to titrate the level of sedation. Butorphanol (5–10 mg) could be added to the infusion to provide addi-


AAEP PROCEEDINGS  Vol. 64  2018 271


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