HOW-TO SESSION: FIELD SURGERY - SOFT TISSUE AND WOUND MANAGEMENT


Although placing an IV catheter is not a common practice in the field, it certainly makes dealing with difficult situations easier. The author recommends having 14-gauge 3.5” and 18-gauge 3.5” short-term catheters available as well as two additional doses of ketamine in 3-ml syringes and an additional 3-ml sy- ringe of xylazine. Reversal of alpha-2 agonists is rarely necessary and not recommended unless inad- vertent overdosage occurs. Adequate sedation is essential prior to induction


of anesthesia as it is not uncommon for recovery quality to mimic induction quality. Sedation with an alpha-2 agonist in combination with butorphanol is recommended as premedication for any procedure involving general anesthesia in the field. The bu- torphanol can improve sedation quality and provide additional analgesia. Induction using ketamine at 2.2 mg/kg combined with IV midazolam or diazepam at 0.02–0.035 mg/kg provides approximately 20–30 minutes of general anesthesia. For longer proce- dures, placing an IV catheter and using the combi- nation of 50 gm guaifenesin, 1 gm ketamine, and 500 mg xylazine (called “Triple Drip”) allows for maintenance of a surgical plane of anesthesia for up to 1 hour. The infusion can be bolused to an adult at approximately 150–300 ml after induction and slowed to a drop per second or slower to main- tain anesthesia. A 1-L bag of 0.9% NaCl or LRS with 50 mg midazolam, 2 gm ketamine, and 500 mg xylazine can be used as an alternative to “triple drip” and administered in the same manner. Recovery in the field is typically smooth due to the


short duration of anesthesia. Most horses will roll to sternal recumbency and then stand after about 15–20 minutes. Place a halter and lead rope on the horse to assist recovery and maintain control. For longer procedures requiring multiple boluses of ketamine or1Lormore of “triple drip,” sedation is recommended prior to recovery. Administer 50– 100 mg xylazine IM near the end of the procedure or 100 mg IV xylazine at the conclusion of the proce- dure. For an excited or nervous horse, a bolus of 3–5 mg IM detomidine 5–10 minutes prior to con- cluding the procedure or 3 mg IV at the conclusion can be effective for maintaining recumbency until the anesthetic agents have redistributed. Addi- tional doses of xylazine or detomidine should be available in case sedation is not adequate to main- tain recumbency until the horse is prepared to stand. In the event that a horse attempts to stand suddenly after the procedure but is not strong enough to maintain its position, allow the horse to fall into recumbency and, if possible, place your knee on the back of the neck until a bolus of 5 mg deto- midine can be administered intravenously. An ad-


ditional bolus of xylazine is rarely adequate to maintain recumbency in an excited horse. In the event of cardiac arrest in the field, imme-


diately attempt cardiac compressions at a rate of 60–80 compressions per minute. The horse should preferably be in right lateral recumbency and not on a soft surface. Compressions should be aggressive and performed using either your knees or feet, jump- ing with your full force over the rib spaces caudal to the elbow. Epinephrine should be intravenously administered at 3–10 mg, intratracheally (utilizing intubation and an endotracheal tube), or intracar- diacally (using a catheter stylet or spinal needle). Epinephrine can be administered every 3 minutes combined with cardiac compressions until a positive outcome is achieved or multiple attempts at resus- citation over 20–30 minutes have failed. The prog- nosis for resuscitation in adult or juvenile horses from cardiac arrest is poor; existing disease, cause of cardiac arrest, body size, and availability of human assistance and drugs determine outcome.


3. Discussion


Anesthesia should never be considered simple or routine. Even short procedures can become compli- cated. A physical exam prior to sedation, a plan, and additional anesthetic and emergency drugs within reach will improve the chances of a successful outcome.


Acknowledgments


Declaration of Ethics The Author has adhered to the Principles of Veteri- nary Medical Ethics of the AVMA.


Conflict of Interest


Dr. Bidwell has been sponsored by Zoetis for several years as a speaker and consultant for anesthesia lectures and continuing education courses.


Reference and Footnotes


1. Peters DF, Erfle JB, Slobojan GT. Aggressive behavior asso- ciated with the use of xylazine and detomidine, in Proceedings. Am Assoc Equine Pract 1998;284–186.


aDormosedan Gel, Zoetis Animal Health, Parsippany, NJ 07054. bDormosedan, Zoetis Animal Health, Parsippany, NJ 07054. cTorbugesic, Zoetis Animal Health, Parsippany, NJ 07054. dMorphine Sulfate, Fresenius Kabi, Lake Zurich, IL 60047. eRompun, Bayer Healthcare Shawnee Mission, KS 66201. fKetaset, Zoetis Animal Health, Parsippany, NJ 07054. gMidazolam, Pfizer, Lake Forest, IL 60045. hDiazepam, Hospira Inc., Lake Forest, IL 60045.


ington, KY 40511. j


iGuaifenesin, Rood and Riddle Pharmacy Compounding, Lex- Epinephrine, Vedco, Joseph, MO 64507.


kTolazoline, Cayman Chemicals, Ann Arbor, MI 48108.


178 2019  Vol. 65  AAEP PROCEEDINGS


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