Equine Field Anesthesia Flashcards
What should you consider when doing field anesthesia?
- procedural considerations
- environmental considerations
- patient considerations
- equipment (basics, oxygen)
- personnel considerations
what is triple drip?
guaifenesin, ketamine, & xylazine
what are the procedural considerations when doing field anesthesia?
- what is the nature of the injury?
- standing sedation & local block OR GA?
- what is the complexity of the surgery?
- what is the expected duration of the procedure? (top ups; triple drip)
only SIMPLE PROCEDURES of SHORT DURATION should be attempted away from the “relative safety” of the well-equipped & well-staffed hospital
what are the environmental considerations when doing field anesthesia?
- optimal conditions include soft ground & flat/gentle gradient
- avoid man-made or natural hazards: barbed wire fences, farm equipment, ponds, streams, ravines
what are the patient considerations when doing field anesthesia?
- thorough hx & physical exam (cardiovascular & respiratory systems, gut motility, pain)
- stabilization (hemorrhage, fasting)
- weight estimation (drug dosages require an accurate weight)
- owner consent
How do you estimate a Eq weight in the field?
weight tape & calculate
What should be included in the minimum anesthesia equipment for field anesthesia?
- IV catheters
- sufficient amount of drugs
- soft ropes w/ an appropriate halter
- small towel (covering/protecting eyes)
- E-tank w/ nasal insufflation (full tank holds 625 L of oxygen)
- Eq are v prone to hypoxemia during GA (V/Q mismatch)
what are the personnel considerations when doing field anesthesia?
- you are not only responsible for the safety of the horse but also the safety of the owner & every other individual involved
What to use for sedation/premedication in a Eq?
- acepromazine
- A2 agonists
Acepromazine in Eq field anesthesia?
- IV/IM
- may be useful as a “pre-med” often in combo w/ other drugs
- can be used alone for non-painful procedures
- provides anti-arrhythmic effect
- sufficient time should be allowed for it to work (30-40 MINS)
- vasodilation & hypotension does occur (A1 antagonism)
- penile prolapse (should be avoided in breeding stallions)
What is important about A2 agonists in equine field anesthesia?
Xylazine, Detomidine, Romifidine
- provide more reliable sedation
- also provide analgesia & muscle relaxation, some ataxia
- equipotent doses of the 3 different A2 agonists used in Eq
- STANDING SEDATION (use low dose) & PRE-ANESTHETIC MEDICATION (usually use high dose)
What are the cardiovascular effects of IV administration of an A2 agonist in equine field anesthesia?
- bradycardia does not require atropine in Eq or Ru
- wait a few minutes & HR will increase
What is important about A2 agonist drugs & their combinations for sedation in equine field anesthesia?
- A2 agonists used ALONE (DO NOT TRUST - Eq can still kick)
- A2 agonists w/ OPIOIDS: BUTORPHANOL (IV); morphine (use a longer lasting A2 agonist); can mix drugs OR give drugs seperately
- A2 agonists w/ OPIOIDS & ACEPROMAZINE (IV): DETOMIDINE + BUTORPHANOL + ACEPROMAZINE MIX IS COMMON; detomidine + acepromazine is good for mares; romifidine mixed w/ acepromazine = precipitation (DO NOT administer)
What are the steps in induction of anesthesia in equine field anesthesia?
- pre-anesthetic preparation: fast 12 hrs (minimum fast 6 hrs prior to surgery); water until 1 hr before; medical history; physical exam; clinical hematology as necessary
- assess facilities/enviro
- place an IV catheter
- check halter & ropes
- protect facial nerve if leaving halter on the head
- select site (brief the help on safety & potential problems)
What are the common anesthetic field induction protocols?
- xylazine OR detomidine (IV): WAIT A FEW MINS FOR PEAK SEDATION
- Diazepam + Ketamine (mix)
- diazepam is optional but does “smooth” induction
- butorphanol (IV) can be added (often wait until Eq is induced to minimize the potential for excitement)
- consider local anesthetic techniques
Induction w/ ketamine in equine field anesthesia?
- NOSE TO KNEES sedation before induction w/ ketamine
- check HR
- DO NOT INDUCE W/ KETAMINE IF: sedation is poor (top up sedation w/ A2 agonist); HR is extremely low (wait until it comes back up (2-3 mins))
How to move into recumbency in equine field anesthesia?
- dont allow head to smack the ground
- check vital signs & anesthetic depth
- position for procedure
- protect eyes
- protect cranial nerves (remove halter)
What are our options to maintain anesthesia in equine field anesthesia?
- incremental top-up IV bolus
- CRI
How do we maintain anesthesia with Top-Ups in equine field anesthesia?
Ketamine + xylazine
- mix 1/3-1/2 of the premedication & induction doses
- this may provide 2-3 top ups
- given every 10-15 mins depending on depth of anesthesia
- ketamine is slightly cumulative (after the 3rd top up, the dosing interval should be increased OR subsequent doses decreased)
How do we maintain anesthesia with Triple-Drip in equine field anesthesia?
- indicated when we need a little longer duration of anesthetic time
- max anesthesia time approximately 90 mins
- Guaifenesin + xylazine + ketamine
- good for procedures up to 60 mins (ideally w/ OXYGEN & good positioning)
- cardiopulmonary stability
- good analgesia
- easy to use
- good recovery
How do you check the depth of anesthesia in equine field anesthesia?
- pulse quality, mucous mb colour, CRT, HR
- respiratory rate & depth
- check eye reflexes (palpebral reflex is “brisk”)
- in a LIGHT plane of anesthesia if: spontaneous blinking, tearing, nystagmus
- don’t use corneal reflexes
How do you monitor during equine field anesthesia?
- portable equipment
- measure BP w/ doppler & sphygmomanometer
- use pulse oximeter
How do we administer life support in equine field anesthesia?
- usually short procedures are attempted in the field
- refer long procedures
- if anticipating a longer procedure, consider oxygen & fluids
How does recovery work in equine field anesthesia?
- usually dont use reversal
- control recovery
- keep safety of people in mind
- avoid noise
- keep eyes covered
- consider sedation (xylazine) if recent ‘top-up’ w/ ketamine alone in the previous 10 mins
- if longer procedure, consider placing a urinary catheter & emptying the bladder
What do we use for analgesia in equine field anesthesia?
- NSAIDs (used pre-emptively to minimize surgical/inflammatory pain)
- opioids: provide good analgesia & increase sedation (BUTORPHANOL - IV, provides 60-90 mins analgesia; MORPHINE - IM or SLOW IV, provides 2-4 hrs analgesia; BUPRENORPHINE - IM, provides up to 12 hr analgesia, onset 30-45 mins)
- local anesthetic blocks: can provide a useful part of a balanced analgesia; intra-testicular for castration
