Equine anesthesia Flashcards
What should you use for light sedation of a horse
Acepromazine alone or mixed with opioid (butorphanol)
Low dose alpha2 - agonist
Xylazine, detomidine, romifidine
What do you use for heavy sedation of a horse
Higher dose alpha2-agonist
+ Opioid
Butorphanol
Avoid using opioids without sedatives in non-painful horses = excitement
+ acepromazine
Added to alpha2 - agonist and butorphanol for fractious horses
Ace as sedation in horses
Used alone for non-painful procedures
Can be used with alpha2-agonists and opioids
Onset of action is SLOW
IV (1o minutes)
IM (20 minutes)
Cardiovascular effects = VASODILATION from alpha1 - blockade:
Do not use in hypovolemic animals
Other notable side effects = potential to cause penile prolapse
Do not use in breeding stallions
Alpha2 adrenergic agonists for sedation in horses
Equipotent doses of 3 different alpha2 agonists used in horses
- Produce the same effect
- Duration may differ
Low dose
- Xylazine (0.2-0.5 mg/kg)
- Detomidine (0.005-0.01 mg/kg)
-Romifidine (0.03-0.05 mg/kg)
High dose
-Xylazine (1.0 mg/kg)
- Detomidine (0.02 mg/kg)
- Romifidine (0.1 mg/kg)
Cardiovascular effects of IV administration of xylazine in horses
Duration of sedative effects
Xylazine lasts 20 min
Romifidine and detomidine lasts about 40 min
Alpha 2 - agonists drug and combinations for sedation
commonly used in horses
Alpha2-agonists used ALONE
- Do not trust- horse can still kick
Alpha2-agonists combined with opioids
- Butorphanol
- Morphine (use a longer acting alpha 2 agonists)
Alpha2-agonists with opioids and acepromazine
- detomidine/butorphanol/acepromazine mix is common
-Detomidine/acepromazine is a good mix for mares
- Romifidine mixed with acepromazine - precipitates- DO NOT administer
Detomidine and butorphanol is commonly used for what in horses and causes
Common combination for standing sedation
- Oral exam
- Eye exam
- Teeth floats
- Laceration repairs with a local block
Detomidine (10mcg/kg) + butorphanol (0.02mg/kg) IV
The opioid may cause some excitement
- Muscle twitching (“torb twitches”)
- Excited look in eyes
- Increased pacing (locomotor activity)
- Explosive behaviour
Can give the alpha2-agonists first to minimize excitement effects of OPIOID
What do you use for long standing sedation in horses
For longer procedures - two options
- Top ups
- Infusions
detomidine/butorphanol – common combination
- Put drugs in bag of fluids – administer to effect
- Urination frequent and annoying side effect
Can be difficult to maintain ideal conditions
-Horse needs to stand
- Ataxia can occur - horse fidgets, slumps, leans on the stocks
What is commonly used in field anaesthsia in horses
Alpha2-agonist for sedation (premed)
Ketamine used for anaesthesia
Fast for 8-12 hours
Field anesthetic induction protocol for horses
Xylazine (1mg/kg IV) OR detomidine (10-20 microg/kg IV)
Wait a few minutes for peak sedation
Mix diazepam (0.02 mg/kg IV) and ketamine (2-3 mg/kg IV)
Diazepam is optional but does smooth induction
Butorphanol (0.02 mg/kg IV) can be added
Safest time to administer is once the horse is induced – minimize potential for excitement and a possible stormy induction
After sedation – before administration of ketamine – look for
Obvious signs of sedation (‘nose to knees’) – if sedation is poor give more
Check HR
How do you place a horse in recumbency
Don’t allow head to smack the ground
Check vital signs and anaesthetic depth
Position for procedure
Protect eyes
Protect cranial nerves – remove halter
Maintenance of injectable anaesthesia is doen how in horses
BOLUS technique
Mix 2 ml xylazine with 4 ml ketamine in syringe
Provides 2-3 ‘top ups’
Dose depending on depth of anaesthesia
Infusion technique = triple dip
Maintenance with infusion of Triple-Dip in horses is done how
In 1 liter 5% Guaifenesin–add:
500 mg Xylazine
1000 mg Ketamine
Give at rate of about 2 mL/kg/hr
Good for procedures up to 60 minutes:
Should supplement oxygen when horse is recumbent for extended periods
Do NOT administer longer than 2 hours – GGE accumulates
Cardiopulmonary stability
Good recoveries
how do you know how deep a horse is
Pulse quality, color mucous membranes, HR
RR and depth of breathing
Check eye reflexes
‘Light’ plane has:
Spontaneous blinking
Tearing
Nystagmus
Surgical plane:
Ketamine based anesthetic-palpebral reflex ‘brisk’
Inhalational based anesthetic – palpebral reflex ‘sluggish’ OR absent
DO NOT use corneal reflexes – can cause ulcers
What do you use in teh field to monitor a horse
Portable equipment
Measure blood pressure with doppler and sphygmomanometer
Use pulse oximeter
How do you recovere a horse
Personnel safety is important
DO NOT reverse alpha2-agonist
May even ‘top – up’ alpha2-agonist sedation for recovery
Can hold tail and head rope if safe to do so
Avoid noise
How do you se inhalation anaesthsia in horses
Specialist referral practice
Anesthetic machine and ventilator
Use Isoflurane
What are common IV infusions used in horses
Dexmedetomidine
- Ketamine
- Lidocaine
-Morphine
Intensive management of life support for horses include
- Oxygenation and ventilation
- Blood pressure support
-Dobutamine infusion
-Fluid therapy
Equipment for inhalation anesthesia for horses
Large animal circle system with ventilator:
Hoses wider than diameter of trachea
Use similar oxygen flows (2–6 L)
Go through a lot of Isoflurane–always check supplies:
May need to refill vaporizer part way through procedure
Induction and recovery areas required
Padded tables required
How do you use a pulse ox in horses
Cyanosis may not be easily detectable in horses
Mucus membranes can look pale from vasoconstriction, hypotension
Horses saturate hemoglobin slightly better than humans, so pulse oximeter may under-estimate
Still consider <90% indicative of hypoxemia
Place probe carefully so transmitter and receiver line up
Head-down position can cause venous congestion and pulse oximeter cannot detect signal
Peripheral vasoconstriction limits signal quality
How do you do direct arterial BP in a horse
Catheterize a peripheral artery
Facial, transverse facial, coccygeal, metatarsal, auricular
Allows arterial blood gas analysis (electrolytes etc.)
Connected using non-compliant, saline-filled tubing to a transducer and electronic display
Provides continuous systolic, mean diastolic waveform
Flush system keeps catheter patent
Minimum MAP > 70 mmHg
How do you use a capnograph in a horse
Normal conscious value of PaCO2 is 40-45 mmHg
Anesthetized horses prone to respiratory depression
Can use a ventilator
PaCO2 found to rise by 4 mmHg/min in horses with apnea
Arterial CO2 to ET CO2 gradient normally 1-2 mmHg, but is ~11 mmHg in anesthetized healthy horses
Indicates increased alveolar dead space:tidal volume ratio
Increased PaCO2 not immediately life-threatening
How do you do fluid therapy in horses
Important to provide fluid therapy for long anaesthetic periods
Helps improve tissue perfusion
Generally use 5-10 ml/kg/hr (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
