Page 40 - Manual of Equine Field Surgery

36 PRESURGICAL PREPARATION AND ASSESSMENT

CX.2-Agonists can be combined with Telazol. longed and the horse is unable to get up but does

The cx.2-agonist should be administered first and not appear sedate, fluids should be administered

Telazol is administered only after the horse is in an attempt to improve excretion of the drugs

sedate. Xylazine ( 1.1 mg/kg IV) can be combined and their metabolites.

with Telazol ( 1.65 mg/kg IV) to produce general Detomidine can be used with guaifenesin and

anesthesia of approximately 20 to 30 minutes.62•71 ketamine after induction with detomidine and

Alternatively, detomidine can be used. Detomi- ketamine.P-" The preparation used contains ket-

dine at doses of 0.02 mg/kg or 0.04 mg/kg IV amine (2 mg/mL) and detomidine (0.02 mg/mL)

followed by Telazol (2 mg/kg IV) produced ap- in lOo/o guaifenesin administered at approxi-

proximately 25 and 30 minutes of anesthesia, mately 1 mL/kg/hr. If 5°/o guaifenesin is used, the

respectively.62 Xylazine (0.44 mg/kg IV) can be ketamine and detomidine concentrations should

followed by a mixture of Telazol dissolved in deto- each be reduced by one half (1 mg/mL and 0.01

midine and ketamine to produce recumbency of mg/mL, respectively). The infusion rate for the

approximately 40 minutes.72 A 500-mg bottle of less concentrated mixture is 2 mL/kg/hr.

Telazol is dissolved in 4 mL of 100 mg/ml, keta- Romifidine with guaifenesin and ketamine has

mine and 1 mL of 10 mg/mL detomidine. Three been used as a maintenance anesthetic following

milliliters of the mixture per 450 kg of body induction with romifidine and ketamine.78 The

weight is the recommended dose. induction dose is 0.1 mg/kg of romifidine IV fol-

lowed by 2.2 mg/kg of ketamine Iv. The mainte-

a2-Agonist-Dissociative-Guaienesin nance infusion consists of an initial bolus of 50
f

Combinatons mg/kg of guaifenesin followed by IV infusion of
i
romifidine (0.0825 mg/kg/hr), ketamine (6.6 mg/

The combination of guaifenesin, ketamine, and kg/hr), and guaifenesin (100 mg/kg/hr). After 30

xylazine (GKX), or "triple drip," has been used for minutes, the guaifenesin infusion rate is decreased

many years in equine anesthesia. This combina- 50%.

tion was first described as an induction cornbina-

tiori" and later as a maintenance anesthetic. 74

When used as a maintenance anesthetic, 0.5 Thiopental-Guaifenesin Combinations

mg/ml. of xylazine and 1 or 2 mg/mL of ketamine The use of guaifenesin with thiopental allows the

are added to a 5% solution of guaifenesin in use of a lower dose of thiopental and usually pro-

dextrose. One liter of 5% guaifenesin would have duces better recovery than the use of thiopental

5mL of 100 mg/mL xylazine and 10 or 20mL of alone. Induction is usually preceded by the

100 mg/mL ketamine added. It should always be administration of an cx.2-agonist st1ch as xylazine

administered through a catheter because extravas- or detomidine. Both thiopental and guaifenesin

cular guaifenesin can cause severe tissue damage. will cause tissue damage. Therefore, it is essential

In addition, the vein used for administering the this mixture be administered via an indwelling IV

anesthetic should not be occluded so blood can catheter located in a vessel with good blood flow.

flow freely to allow distribution of the drug and A I-l-gauge or larger catheter is recommended to

prevent thrombophlebitis. Triple drip can be used allow the rapid administration of the thiopental-

as an induction agent in horses sedated with guaifenesin mixture. To administer this mixture,

74
xylaxine. More commonly, however, it is used as 2 g of thiopental is added to 1 L of 5% guaifen-

a maintenance anesthetic following induction esin. 64 This mixture is then administered IV as

with xylazine and ketamine as described earlier in rapidly as possible until the horse is recumbent.

this section. It is infused at a rate that produces To speed induction, 1 additional gram of thiopen-

the desired level of anesthesia, but the mainte- tal can be administered IV as the horse begins to

nance infusion rate is usually 2.2 to 2.75 mL/kg/hr relax. If drug administration is stopped after the

(approximately 1 mL/lb/hr).60•64'74 The higher con- horse is recumbent, the duration of anesthesia

centration of ketamine allows slightly slower will be 10 to 20 minutes. Additional anesthesia

infusion rates for longer procedures. This is an tune can be produced by continuing the infusion

appropriate anesthetic technique for up to 90 to effect. The typical infusion rate will be approx-

minutes in healthy horses. If the recovery is pro- imately l.5mL/kg/min.64 If more than lL of the

longed, tolazoline can be used to antagonize the mixture is to be used, the second liter should only

sedative effects of xylazine.75 If the recovery is pro- contain 1 g of thiopental (1 mg/mL). Total anes-