Anesthetic Considerations in the Horse Flashcards
(47 cards)
general considerations of anesthesia in a horse
- challenging
- higher morbidity and mortality
- potential for injury to themselves and staff
special features of horse anesthesia
- size
- behavior
- CV function
- resp function
- GI system
- recovery
- pain management/anesthetic protocols
why is horse size challenging with anesthesia?
- handling/restraint
- moving/positioning
- neuro/myopathy
- ventilation/perfusion mismatch
- different drug response
horse behavior w anesthesia
- fight or flight response: self destructive nature, affects induction and recovery
- quiet environment!
- experienced handling to minimize risk
what effects do anesthetics have on horse CV system
- depressant: decrease myocardial contractility, decrease CO by 40% = decreased BP
- poor tissue perfusion: post anesthetic myopathy
- inotropic support is key! dobutamine is most common
what kind of support is key in horses to support CV function?
inotropic support: want to support heart contractility: dobutamine is most common
anesthesia’s effects on resp fx in horses
- resp depressant
- HYPOVENTILATION: common
- abdominal distension
- position: head down
- mechanical ventilation often needed
how do anesthetics affect oxygenation of horses?
- severe V/Q mismatch: physiological shunt, low PaO2, hypoxemia
- positioning matters! esp when pt on side or back
- often need mechanical ventilation and oxygen
how can you help severe V/Q mismatch in recovery with an anesthetized horse?
- O2 insufflation thru endotracheal tube: can stand with it; easy way to supplement O2
- demand valve: provides high flow: 100% O2 to give horse a breath, can inflate lungs in recovery
why are horses at risk of obstruction in recovery?
- they are obligate nasal breathers
- nasal congestion (why we recover with tube in)
- keep intubated! wait for swallow reflex and standing and then pull tube
- can spray phenylephrine on nares (horse is vasodilated from drugs, venous congestion can occur, get discharge, phenylephrine is a alpha 1 agonist and will cause vasoconstriction)
a 2 year old healthy quarter horse mare is anesthetized with sevoflurane for arthroscopy. in recovery the horse has a difficult time rising and you notice that the gluteal muscles are firm, swollen and very painful. which of the following is the most like cause if it occurred for an extensive period:
a. HR of 50 bpm
b. MAP of 50mmHg
c. PaCo2 of 50 mmHg
b.
A: little high but not enough to impact filling. if at 70, would worry
B: we worry bc don’t want myopathies to happen! need to ensure that muscles are perfused. between 75-85 is ideal range
C: horses can be hypercapneic: this # is not uncommon
what is the ideal BP for an anesthetized horse?
between 75-85mmHg. small: 75. draft: 80-85.
how does the horse GI system affect anesthesia?
- large colon = fermentation vat
- distension from gas or feed
- compromised cardiopulmonary function!
- preoperatory fasting? to decrease food, less to ferment and decrease pressure: didn’t show complications tho and had faster return to normal in non-fasted patients…
Co2 will be increased and O2 decreased: not able to ventilate well
anesthetic risk with GI in horses
- decreases GI motility: stress, drugs, transport, PAIN
- increases risk of ILEUS! opioids risky
blocks can help
recumbency in horses
- long periods of recumbency is not normal: increases risk of myopathies, neuropathies, and get V/Q mismatch
- good padding is very important!!
- need to stand within 1 hr of anesthesia?
when do we want to see horses stand after anesthetic procedures?
stand within 1 hr after anesthesia! horses MUST stand after anesthesia
recover with ET tube in place to prevent airway obstruction!!
recovery complications in horses
- complications: fractures and injuries from attempts to stand, upper airway obstruction
- quest for the perfect recovery technique may not exist
what can we do to improve recovery for horses?
- maintain airway (ETT)
- prevent hypoxemia (O2 insufflation)
- padded recovery stall
- additional sedation
- assist recovery if indicated
what are common sedation protocols for horses?
- alpha 2 agonists: xylazine, detomidine, romifidine, dexmedetomidine
- acepromazine (10-20 min prior)
+/- opioid: butorphanol, hydromorphone, morphine. give a lil sedation FIRST, then opioid because opioid will deepen their sedation.
butorphanol is most commonly used in horses, good sedative but not great for pain. hydro is best for pain: lasts longer and less impact on GI than morphine
what opioid is best for painful procedures in horses?
hydromorphone: lasts longer and less impact on GI than morphine
what is common induction protocols for horses?
- ketamine: can give AFTER sedation. doesn’t have muscle relaxation!
- ketamine + diazepam/midazolam (these are muscle relaxants)
- ketamine + propofol: preferred
- ketamine + guaifenesin
- ketamine + guaifenesin + diaz/midaz
ketamine and muscle relaxant is best: get relaxation, and decreases amount of ketamine needed. don’t do propofol alone! harder to modulate
what is the preferred induction protocol for horses?
ketamine + propofol
how do we maintain anesthesia in a horse?
- TIVA: total intravenous anesthesia
- inhalant anesthesia (IA)
what is total intravenous anesthesia?
- way of maintaining it in the horse
- IV top ups (ketamine/xylazine): 1/2 to 1/3 of induction dose
- “triple dip” or GKX/MKX: for longer anesthestic
^ ketamine + muscle relaxant + alpha 2 agonist
^ ketamine + guaifenesin or midazolam + xylaxine
