Equine Field Anesthesia

what equipment falls under the airway category?

endotracheal tube, cuff inflator and block gag, large syringe for oral flushing

what equipment falls under the breathing (ventilation) category?

demand valve and oxygen cylinder/regulator

what equipment falls under the circulation category?

IVC, injection port(s) ± extension set, suture materia

what equipment falls under the drugs category?

premed (alpha 2), induction, maintenance (triple drip), top-ups, flush and syringes, emergency drugs

what premed is typically used in horse field anesthesia?

alpha 2 agonists — xylazine, detomidine, romifidine

what induction agents are typically used?

ketamine + diazepam or proporfol

what top ups might be given?

ketamine or xylazine

what emergency drugs should you always have?

atropine, adrenaline, IV fluids

what equipment falls under the eyes category?

lacrilube eye ointment, towels for eye and head protection, foam wedge or support to elevate the heat and protect the dependent eye

what equipment or methods do you need for monitoring?

assessing eye signs (nystagmus, blinking, lacrimation) and ear movement

may also use pulse oximetry or blood pressure monitoring

what is triple drip?

maintenance drugs during anesthesia, which includes guaifenesin with ketamine and xylazine

what fasting recommendations should be given to horse owners prior to planned anesthetic procedures?

fasting periods range from 6-18hrs → a full stomach and GIT can impair ventilation during anesthesia

why is placement of an IVC recommended?

• provides reliable venous access

• allows rapid administration of additional drugs if required

• reduces the risk of inadvertent perivascular or arterial injection

why should intubation equipment always be available?

in case of:

• airway obstruction

• excessive respiratory depression

• prolonged anesthesia

• unexpected complications

how long should field procedures ideally be?

no more than 60 minutes as recovery quality can decline significantly after 90 minutes of TIVA

why is xylazine the most commonly used alpha 2 agonist in field anesthesia?

inexpensive, provides ~15 min of sedation, provides analgesia, muscle relaxation, and narcosis

induces vasoconstriction followed by bradycardia and respiratory depression

why would you use detomidine over xylazine?

it produces more profound and reliable sedation and is often preferred for excitable or difficult to handle horses

more potent and longer acting than xylazine (30-45min of sedation)

why might acepromazine be used in field anesthesia?

it reduces anxiety in excitable horses and may improve recovery quality

• produces mild sedation that lasts for several hours

• provides mild muscle relaxation

why are opioids not used frequently in horses?

they may increase locomotor activity and excitement

what is butorphanol used for?

used in combination with an alpha-2 agonist to enhance sedation and analgesia during standing procedures and before induction

which NSAIDs are commonly used in horses?

phenylbutazone and flunixin meglumine

→ should be administered for painful procedures unless contraindicated

why is ketamine the most common induction agent used in field anesthesia?

inexpensive, reliable and well suited to short anesthetic periods

why is ketamine combined with an alpha-2 agonist and a benzodiazepine for induction?

ketamine alone provides poor muscle relaxation so the alpha 2 agonist provides sedation, analgesia and some muscle relaxation

addition of a benzodiazepine results in smoother induction, better muscle relaxation, less rigidity and paddling, and longer duration before top-up dosing is needed

what are the most commonly used maintenance techniques for field anesthesia?

triple drip and ketamine/alpha-2 agonist combinations

how can TIVAs be administered in the field?

• continuous infusion — triple drip combo (guaifenesin, xylazine and ketamine)

• intermittent infusion — xylazine and ketamine (“top up” method)

triple drip has two common formulations. why might the higher concentration formula be used?

when you need a slightly deeper, less reactive patient (eg painful procedures)

what is the timing of top ups dictated by?

time (every 12 minutes) UNLESS anesthetic depth is excessively light

what are the key parameters to monitor in field anesthesia?

heart rate, respiratory rate, MM color and CRT, anesthetic depth

how is anesthetic depth monitored?

evaluation of responses to stimulation, including the palpebral reflex

what are signs of a light plane of anesthesia?

movement, nystagmus, lacrimation (tearing), spontaneous palpebral reflex, increasing respiratory rate

what are key features of the recovery area?

• free of obstacles, vehicles, equipment and fencing hazards

• large enough for horses to roll and stand safely

• level and non-slip

• soft where possible (grass, sand, well-bedded stable)

• quiet with minimal activity or distractions

what should be done as the procedure concludes?

• stop administration of anesthetic drugs

• remove surgical equipment and drapes

• ensure hemorrhage is controlled

• continue monitoring HR, RR, and MM

• protect the eyes until the horse regains normal reflexes

how should a horse be positioned for recovery from anesthesia?

in lateral recumbency with the head and neck extended and the lower/dependent forelimb pulled forward

what complications are associated with injection of drugs into the carotid artery?

drugs will be delivered directly to the brain and can result in:

• excitement

• seizures

• respiratory arrest

• cardiac arrest

what might perivascular injection cause?

• tissue irritation or damage

• delayed drug absorption

• unpredictable induction or recovery

if deposited near the recurrent laryngeal nerve, it may cause laryngeal paralysis

what can rhabdomyolysis result in?

• release of myoglobin can cause acute kidney injury (AKI) — refer!

• clinical signs include stiffness, lameness, muscle swelling, reluctance to stand or move

when is neuropathy risk the greatest?

• in large horses

• during prolonged anesthesia

• at pressure points

• in the dependent limbs during lateral recumbency

what clinical signs are associated with neuropathy?

weakness, knuckling, or difficulty standing after recovery

what measures can be taken to reduce the risk of rhabdomyolysis or neuropathy in horses?

padding, positioning (avoid lateral recumbency as much as possible), pull the dependent forelimb foreward

how might a horse injure itself during induction, recumbency or recovery?

skin abrasions, lacerations, fractures

→ most injuries occur during recovery when substantial forces are placed on the limbs during attempts to stand