Exam 4: Lecture 26 - Equine Anesthesia Flashcards
prior to modern day anesthesia, what did we use for horses
heavy physical restraint and herbal remedies
what are some of the physical restraints used prior to modern day anesthesia in equines
hobbles, casting harness, ropes
___1___ became widely used in vet med after 1845 and ____2___ after 1847
- chloroform
- ether
after ___1______, equine anesthesia really started to evolve into a more specific process which had the development of new drugs
1950
what happened in 1955 for equine anesthesia
succinylcholine was used for short surgical procedures
what is succinylcholine
a depolarizing neuromuscular blocking drug
what happened in 1957 for equine anesthesia
Halothane first used in horses
what happened in late 1960s for equine anesthesia
Guaifenesin used to reduce the dose of thiopental and subsequent cardiovascular depression
what happened in early 1970 for equine anesthesia
xylazine was introduced
what are the components of our preoperative eval for equine anesthesia
- history
- concurrent meds
- PE
- lab data
- ASA assigned
- fasting (withhold food for 3-6 hours)
what things factor into our patient prep
- IV access should always be in place prior to anesthesia
- flush food debris out of mouth
- clean feet and remove/tape over shoes
- perioperative abx, anti-inflammatories, and tetanus prophylaxis given 30 mins prior to sx
- clip hair over sx site
- fluid resuscitation prior to anesthesia if dehydrated or in shock
what is the BIGGEST consideration for equine anesthesia
safety first
Other than safety, what are some other considerations for equine anesthesia
- behavior
- adequate staff/facilities
- increased anesthetic risk in horses
- anatomy and physiology
what are the important things to remember about the anatomy and physiology in equine anesthesia
- obligate nose breathers
- prone to V/Q mismatch and hypoxemia
- GI tract considerations
- Large muscle mass and body weight can lead to development of myopathy and/or neuropathy
what are the 10 things that increase risk of anesthesia in equines
- fracture repair
- young (<1month) or old (>14 yrs)
- colic and/or emergency surgery
- surgery between midnight and 6am
- experience of surgeon
- duration of anesthesia
- trauma, dehydration, stress, poor condition, systemic disease
- pregnant
- drug choices
- breed predisposition (EX: HYPP, myelomalacia)
what is the newer tool called that is used for pre-anesthetic risk that accounts for additional factors unique to horses
CHARIOT (combined horse anesthetic risk ID and optimisation tool)
what are the respiratory considerations for equine anesthesia
- they are prone to compression atelectasis in dorsal recumbency
- all anesthetic drugs depress respiratory drive, muscle function, ventilatory rate/volume
- inhalant anesthetics alter the distribution of pulmonary blood flow
- upper airway obstruction from nasal edema is expected after prolonged sx
why does the fact that inhalant anesthetics alter the distribution of pulmonary blood flow matter in equine anesthsia
it abolishes hypoxic pulmonary vasoconstriction resulting in areas of the lung that are perfused but not ventilated which worsens the hypoxemia by contributing to a V/Q mismatch
what are the 3 cardiovascular considerations for equine anesthesia
- second degree AV block is generally normal and is due to high vagal tone
- horses have a large SA node so a wandering pacemaker is common
- atrial mass is large so biphasic P wave is normal but the large size makes atria predisposed to development of re-entrant rhythms
what is being shown in these pictures
atrial fibrillation in a horse
what are the 4 main categories of drugs we use for premed in equine
acepromazine, alpha-2 agonists, opioids, benzodiazepines
Describe when we use ace as a premed and the potential complications
typically used as an adjunct to other sedatives in excitable horses
caution when used in breeding stallions due to potential for penile prolapse
describe what alpha-2 agonists we use as premeds in equine and why
xylazine, detomidine, dexmedetomidine, romifidine
most commonly used for sedation, muscle relaxation, and analgesic
what opioids are commonly used as premeds in equines and what is the benefit of them
butorphanol, morphine, hydromorphone, buprenorphine
less likely to cause excitement when co-administered with alpha-2 agonists or ace
what are the benzodiazepines we use as premeds in equine and are they commonly used
diazepam or midazolam
rarely used by itself except in foals
what are the drugs we use for IV induction in equine
- ketamine + benzodiazepines
- ketamine + guaifensin
- ketamine alone following heavy alpha-2 agonist sedation
- propofol
- telazol
- alfaxalone
T/F: We commonly use propofol in equine anesthesia
false, not commonly used because of cost, large volume needed, and poor quality induction
T/F: Telazol is excellent for induction following alpha-2 agonist sedation but the recovery is rough
true!
T/F: Alfaxalone is commonly used in equine anesthesia
false, has been studied in horses but is very expensive!
what drugs are used for maintenance of anesthesia in equine
isoflurane and sevoflurane
what do we use a lidocaine CRI for in equine anesthesia
improves analgesia and GI motility, reduces MAC by ~ 25%
what is the benefit of a morphine-lidocaine-ketamine CRI in equine anesthesia
can reduce MAC by 50%
when is a dexmedetomidine CRI used in equine anesthesia
for prolonged standing sedation
what is the rate we should use crystalloids for in equine anesthesia
replacement fluids (isotonic): 5-10 ml/kg/hr
hypertonic saline 2-4 ml/kg over 15 mins for emergency resuscitation of hypovolemia
what is the problem when using fluids in foals
foals are not able to compensate for increased fluid load and may retain fluids leading to edema
T/F: scavenging can be active or passive for equine anesthesia
true! charcoal canisters become ineffective at high fresh gas flow rates that are used for adult horses
what type of equipment should we have for equine anesthesia
hydraulic lift on a sx table, soft ropes to tie limbs, oxygen demand valve, padded recovery stall/sling
what are things we should keep in mind for the induction period
- designated space for induction
- owner kept at a safe distance and explain what is going to happen with their horse
- keep noise level down
- BE SURE YOUR PATIENT IS ADEQUATELY SEDATED
what person during induction has the MOST responsibility
person on the head
how do we do an induction using an induction stall with swing gate
keep the head steady until patient begins to buckle at the knees and then push head up to make the horse “dog sit” before coming down on the front legs
how do we do an induction using a free-fall induction
once the horse begins to buckle and relax before falling, turn the head the OPPOSITE direction of how you want the horse to lay
what position do we have the horse in for a blind intubation
lateral or in sternal recumbency
what size ET tube do we use for the average adult
26mm
what size ET tube do we use for larger horses
30mm
what size ET tube do we use for the newborn foal
10-11mm
what size ET tube do we use for a donkey
14-16mm
what size syringe should we use to inflate the cuff for equine ET tubes
60cc
what should we ALWAYS be prepared for with equine anesthesia
always be prepared for them to become light and start to move!!!
what do we do if the equine patient becomes light and starts to move
- communicate to surgeon to stop stimulation and all available hands to safety hold patient on table
- give a rapidly acting injectable anesthetic like propofol or ketamine
- increase vaporizer and O2 flow rate, give IPPV
- consider adding in a local anesthetic block if possible
what are the physical signs of anesthetic depth in equines
- eye signs such as palpebral and corneal reflexes, lacrimation, nystagmus, position of eyeball
- muscle tone, movement of limb
- swallowing
- ear movement
- anal sphincter tone
- response to surgical stimulation
- shivering or stretching
- respiratory rate, HR, BP are less reliable
T/F: We should physically or visually monitor our patient during equine anesthesia
true!!
where do we place the leads for a base-apex electrocardiogram
negative electrode on the right jugular furrow, positive electrode on left thoracic wall in area of left ventricular apex
what did the study done in 1987 show a direct link between
arterial hypotension and post-anesthetic myopathy
what is the treatment of hypotension for equines
lighten anesthetic depth, administer a positive inotrope to effect or ephedrine, correct volume deficits, change anesthetic regimen to PIVA
what is the normal HR for equines under anesthesia
30-45 bpm
what is the normal RR for equines under anesthesia
6-20 bpm
what is the normal CRT for equines under anesthesia
<2.5 secs
what is the normal temp for equines under anesthesia
> 98 and <101
what is the normal arterial pH for equines under anesthesia
7.35-7.45
what is the normal PaCO2 for equines under anesthesia
40-60mmHg
what is the normal PaO2 for equines under anesthesia
100-500mmHg
what is the normal ETCO2 for equines under anesthesia
30-50mmHg
what is the normal MAP for equines under anesthesia
70-80mmHg
what is the normal CO for equines under anesthesia
30-50 ml/kg/min
what are the 3 things we need to consider during recovery of GA in equines
- communicate with the sx team so you can coordinate movement to the recovery area
- this is still a potentially life-threatening time period for the horse
- administer a dose of alpha-2 agonist as the inhalant is discontinued
how long does recovery take for equines that underwent general anesthesia
it varies by the patient, duration of procedure, drugs used, body temp, etc but generally about 30 mins
what type of recovery is being shown here
pool recovery
what type of recovery is being shown here
rope assisted recovery
what are the 9 “keys” to equine anesthesia success
- understand its risky
- have/develop horse sense
- know your pharmacology and physio!
- keep MAP > 70-80 mmHg
- adequate padding and positioning
- maintain patent airway
- keep sx less than 3 hours
- safety is IMPORTANT
- be prepared for the worst case scenario
