11. Equine Anesthesia Flashcards
For light sedation of the horse, what is typically used?
Acepromazine alone or mixed with opioid (butorphanol)
A low dose A2 agonist - xylazine, detemodine, romifidine
What is used for heavy sedation in horses?
higher dose A2 agonist
+ opioid: butorphanol, avoid opioids w/o sedatives in non-painful horses = excitement
+ acepromazine - added to A2 agonist AND butorphanol for fractious horses
What is the MOA, onset of action and effect of using acepromazine for sedation?
used alone for non-painful procedures
can be used w/ A2 agonists and opioids
Onset is slow: IV 10m, IM 20m
CV effects: vasodilation from A1 blockade: DO NOT USE IN HYPOVOLEMIC ANIMALS
can cause penile prolapse so don’t use in breeding stallions
What are the cardiovascular effects of IV administration of xylazine in horses?
Duration of sedative effects - xylazine lasts about 20m, romifidine and detomidine about 40m
What are some combinations for sedations when using A2 agonists?
can be used alone - but some animals can override it, don’t trust it, you can still get kicked
A2’s w/ opioids - butorphanols, morphine (use a longer acting A2)
A2’s w/ opioids + acepromazine
Detomidine/butorphanol/ace common
Detomidine/ace - good for mares
romifidine mixed w/ ace - precipitates - DO NOT ADMINISTER
What is the indications of detomidine and butorphanol?
combo for standing sedation for oral and eye exams, teeth floats, laceration repairs w/ a local block
Opioid may cause some excitement like muscle twitching (torb twitches), excited look in eyes, inc pacing (locomotor activity), explosive behaviour
Can give A2 agonist first to minimize excitement effects of opioids
What do you do when you have long standing procedures?
top ups or infusions
Detomidine/butorphanol is common combo, so put drugs in bag of fluids and administer to effect, urination frequent and an annoying s/e
can be difficult to maintain ideal conditions - horse needs to stand
Ataxia can occur - horse fidgets, slumps, leans on the stocks
What might be used for field anesthesia for sedation and anesthesia?
A2 for premed sedation
Ketamine for anesthesia
Fast for 8-12hours if possible
What is one common field anesthetic induction protocol?
Xylazine OR detomidine - wait for peak sedation
Mix of vetval (ketamine + diazepam)
diazepam optional but does smooth induction
Butorphanol ca be added - safest to administer is once the horse is induced - minimize potential for excitement and a possible stormy induction
After sedation - before admin of ketamine, look for obvious signs of sedation (nose to knees) if sedation is poor, give more, check HR
What do we need to do once the horse is in recumbency?
dont allow head to smack the ground
Check vital signs and anesthetic depth
position for procedure
Check eyes
protect cranial nerves - remove halter
How might we maintain injectable anesthesia?
BOLUS technique: mix 2 mL xylazine w/ 4mL ketamine in a syringe
Provides 2-3 top ups, dose depending on depth of anesthesia
INFUSION technique: triple drip
How do we maintain anesthesia using triple drip infusion?
in 1L 5% guaifenesis, add 500mg xylazine, 1000mg ketamine
Give at a rate of 2mL/kg/hr
good for procedures up to 60m - should supplement O when horse is recumbent for extended periods
Do NOT admin longer than 2 hours GGE accumulates
cardiopulmonary stabilities
Good recoveries
How do we check depth of anesthesia?
pulse quality, color MM, HR
RR and depth of breathing, check eye reflexes
Light plane has spontaneous blinking, tearing, nystagmus*
Surgica plane
Ketamine based - palpebral refles ‘brisk”
Inhalaton based - palpebral sluggish or absent
DO NOT use corneal reflexes - can cause ulcers
How do we monitor on the field?
portable equipment
measure blood pressure w/ doppler and sphygomomanometer
use pulse oximeter
What is important when recovering a horse?
Personnel safety is important
DO NOT reverse A2 agonist
may even top up A2 sedation for recovery
Can hold tail and head rope if safe to do so
Avoid noise
How is inhalational anesthesia done?
specialist referral practice
Anestheic machine and ventilator
use iso
IV infusions used (PVA): dexmedetomidine, ketamine, lidocaine, morphine
Intensive mgmt of life support - Oxygenation and ventilation, BP support - dobutamine infusion, fluid therapy
What equipment is used for inhalational anesthesia?
lg animal circle system w/ ventilator - hoses wider than diameter of trachea
use similar O flows (2-6L)
go thru a lot of iso - always check supplies - may need to refill vaporizer part way thru procedure
induction and recovery areas required
Padded tables required
How do we monitor using the pulse oximetry?
cyanosis may not be easily detectable in horses
MM can look pale from vasoconstriction, hypotension
Horses saturate hemoglobin slightly better than humans, so pul ox may under-estimate
Still consider <90% indicative of hypoxemia
Place probe carefully so transmitter and receiver line up
Head-down position can cause venous congestiona nd pulse ox cannot detect signal
peripheral vasoconstriction limits signal quality
How do we measure using the direct arterial BP measurement?
catheterize a peripheral artery
facial, transverse facial, coccygeal, metatarsal, auricular. allows arterial blood gas analysis (elytes)
Connected using non-compliant, saline-filled tubing to a transducer and electronic display - provides continuous systolic, mean diastolic waveform
Flush system to keep catheter patent
Minimum MAP > 70mmHg
How do we monitor using a capnograph/
normal conscious value of PaCO2 is 40-45mmHg
Anesthetizes horses prone to resp depression - can use ventilator
PaCo2 found to rise by 4mmHg/min in horses w/ apnea
Arterial CO2 to ETCO2 gradient normally 1-2mmHg, but it is ~11mmHg in anesthetized healthy horses - indicates inc alveolar dead space:tidal volume ratio
Inc PaCo2 not immediately life-threatening
What fluid therapy do we use for horses?
important to provide for long anesthetic periods
helps improve tissue perfusion
Generally use 5-10mL/kg/hr or 5L/hr for 500kg horse)
lift bag higher and use gravity effects
use multiple catheters and bags
provide separate dedicated lines for inotropes and vasopressors
