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What are the necessities for equine anesthesia?
smooth/rapid induction and recovery
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What are horses really sensitive to during recovery from anesthesia?
external stimuli
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What does EPAM stand for and what is it?
- equine post anesthetic myopathy
- when there is pressure on a structure it squishes all the blood out and causes poor perfusion which can cause damage to those muscles
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How do we prevent EPAM?
- use padding
- patient positioning
- blood pressure monitoring
- minimize duration of the procedure
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What causes post anesthetic neuropathy in horses?
pressure damage
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What is exertional rhabdomylolysis in horses?
damage to muscles due to a stormy recovery
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Why are horses more susceptible to hypoventilation and what can this cause?
- due to pressure on lungs and not being able to expand lungs all the way
- causes hypoxia and hypercapnia
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When we are doing anesthesia out in the field with a horse what do we always need to make sure we have so we can correct hypercapnia?
should always be capable of intubating and ventilating with oxygen or an ambu bag even in a field setting to create positive pressure ventilation
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What is an ambu bag?
sucks in room air to creat positive pressure ventilation
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Which way should a horse fall when they are being induced for anesthesia and how do we get them to fall this way?
- should fall backwards and not forwards
- push patient up and then back to force them to sit first then lay down
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What types of local/regional anesthesia do we use for horses and what do we usually use them for?
- nerve blocks
- intra-articular
- epidural
- usually used for diagnostic or therapeutic reasons
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What is the most common reason to do a local/regional block in horses?
wound repair
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Where do we give an epidural in horses?
sacrococcygeal space (caudal epidural)
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How long should horses be fasted from food and water before anesthesia?
- food: 8 - 12 hours
- water: 2 hours
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What are intracarotid injections in horses?
- we we are trying to give an injection in the jugular and it accidentally goes in the carotid artery
- consequence of this is usually grave
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What are some of the main reasons to do anesthesia on a horse out in the field?
- wound repair
- castration
- small mass removal
- dentistry
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What is the maximum amount of time you can run anesthesia out in the field on a horse? Why?
- 1 hour
- due to the potential for hypoventilation, myopathy, neuropathy
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What are some of the limiting factors for doing anesthesia out in the field on horses?
- invasiveness of procedure: only do for minor procedures, horses are not hearty in the face of a dirty environment
- inability to manage complications: minimally, consider having endotracheal tube and E-tank or ambu bag on hand to be able to provide positive pressure ventilation
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Where in the field should we do the anesthetic procedure on a horse?
- find a level, grassy area
- don't do it in the barn due to the amount of dust and dirt
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Once we have a horse laying down in the field, what do we need to make sure we protect?
- the eyes
- have a doughnut to lay the eye facing the ground on to limit the amount of dirt that is getting in the eye and lay a towel over the head to protect the other eye from external stimuli like the sun
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What is more involved when doing anesthesia on a horse in a hospital setting?
- preparation
- management and monitoring
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How long can we run anesthesia on a horse in a hospital setting?
several hours
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What do we need to do to prep a horse for surgery?
- grooming: bathe or minimally brush and wipe down, clip and prep site prior to anesthesia
- foot prep: pull shoes to get crap out and pick/wash feet
- rinse mouth
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Are intravenous catheters and fluids something we always do for anesthesia in a horse?
yes, it is not an option like it is in small animalmedicine
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We have to do blind intubations on a horse. What do we do if we are unable to get the endotracheal tube in?
retract endotracheal tube and rotate tube 45 - 90 degrees and try again
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What kind of intubation is commonly used in foals?
nasotracheal intubation
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Once we have the horse anesthetized, how should we position them?
- on adequate padding to prevent myopathies and neuropathies
- maintain limbs perpendicular to body when in lateral recumbency to help maintain adequate perfusion
- pull front legs as far forward as possible to prevent nerve paralysis
- use halter without any metal buckles to prevent pressure points
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What do we monitor on a horse during anesthesia?
- body temperature
- ECG
- HR/PR
- RR
- MM color
- CRT
- blood pressure
- blood gases
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What are the most reliable signs when monitoring anesthesia in a horse?
- gross purposeful movement either alone or as a response to surgical stimulation
- reflex movement in response to surgical stimulation
- increase in HR/BP/RR in response to surgical stimulation
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What are some reliable signs when monitoring anesthesia in a horse?
- history of vaporizer setting
- muscle tone
- palpebral reflex
- pupillary response
- eyeball position
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What are the less reliable signs when monitoring anesthesia in a horse?
- the actual HR, RR, and BP numbers themselves
- pupil size
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What happens with the eyes during anesthesia in a horse?
- horses often tear even when in deep anesthesia
- nystagmus is common during anesthesia
- often desirable to maintain a palpebral reflex in horses but just not a strong reflex
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The blood pressure in a horse under anesthesia should never be below _____. What can we do if it gets low?
- 70 mmHg
- dobutamine can be added to fluids
- increase fluids
- decrease vaporizer setting
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What are the disadvantages and advantages to using the direct monitoring versus indirect monitoring of blood gases in horse anesthesia?
- disadvantages: direct monitoring is not continuous. indirect monitoring does not give you as much information
- advantages: direct monitoring gives you more accurate information on pH, PaO2, PaCO2. indirect monitoring continuously monitors capnography and pulse oximetry
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What are the normal values of pH, PaO2, and PaCO2 in an unsedated horse?
- pH: 7.38
- PaO2: 12 - 14.5 kPa or 90 - 110 mmHg
- PaCO2: 5 - 6 kPa or 38 - 46 mmHg
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When we are using indirect blood pressure monitoring, what is our goal for the ETCO2 in horses and INCO2?
- ETCO2: 35 - 40 mmHg
- INCO2: 0
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When do we consider a horse under anesthesia to have hypoxemia? hypercapnia? hypocapnia?
- hypoxemia: PaO2 < 80mmHg
- hypercapnia: PaCO2 > 45 - 50 mmHg or ETCO2 > 40 - 45 mmHg
- hypocapnia: PaCO2 or ETCO2 < 30 mmHg
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What are some common causes of hypoxemia in a horse under anesthesia?
- inadequate ventilation
- poor cardiac output
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What are some common causes of hypercapnia in a horse under anesthesia?
inadequate ventilation
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What are some common causes of hypocapnia in a horse under anesthesia?
- cardiovascular collapse and shallow breathing (with low ETCO2)
- excessive ventilation
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Where are some common places to place an IV catheter in a horse?
- facial (includes nasal and labial branches upon bifucation)
- transverse facial
- dorsal metatarsal arteries
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What should the oxygen flow rate be for a horse under anesthesia?
- 20 ml/kg/min for induction(average 10 L/min)
- 10 ml/kg/min for maintenance (average 5 L/min)
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What should the breathing rate be of a horse under anesthesia?
6 - 12 breaths per minute
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What should the peak inspiratory pressure be of a horse under anesthesia?
15 - 30 cm H2O on manometer
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What should the tidal volume be of a horse under anesthesia?
10 - 12 ml/kg (or 5 L on average)
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What kind of premeds can we use for a horse?
- anticholinergics
- alpha2 agonists
- guaifenesin
- acepromazine
- opioids
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Do we commonly use anticholinergics as a premed for horses?
no because of the potential for gastrointestinal stasis
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What kinds of alpha 2 agonists do we use for horses?
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When using alpha 2 agonists, what do we need to make sure we monitor?
- monitor for 2nd degree heart block and bradycardia
- evaluate HR prior to and post administration
- HR should be > 24bpm
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Which breeds of horses can we increase the dose of xylazine in and by how much?
- mules and hot blooded breeds
- 10 - 20%
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What is the onset time of xylazine (IV and IM) for a horse?
- IV: 3 - 5 min
- IM: 10 - 15 min
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What is the duration of xylazine for a horse?
- 20 min for analgesia
- 1 - 2 hours for sedative
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What is the onset time of detomidine for a horse? IV and IM
- IV: 3 - 5 min
- IM: 10 - 15 min
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What is the duration of detomidine for a horse?
- 60 min for analgesia
- 6 hours for sedation
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When do we give guaifenesin as a premed to horses?
immediately before induction
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Do we often use opioids by themselves for horses? Why or why not?
- no due to excitability
- commonly combined with alpha 2 agonists
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What are the different ways to induce a horse for anesthesia?
- Ketamine
- Xylazine followed by ketamine (most popular in field)
- GKX (triple drip)
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How do we typically maintain horses on anesthesia?
- inhalants
- repeat dose of xylazine/ketamine (1/3 to 1/2 the initial dose)
- GKX infusion
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How can we keep a horse in a recumbent position for as long as possible?
put some pressure on their neck
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We want horses to be able to successfully stand on their _____ attempt when recovering from anesthesia.
- 1st
- which is why we keep them recumbent as long as possible
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Do we need to provide oxygen to the horse during recovery?
- yes
- high flow (10 - 15 L/min) can be provided through the ET tube or intranasally
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Can horses get laryngospasms?
yes, monitor carefully during extubation
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What can we give horses during recovery to help ease the recovery?
a little bit of xylazine because that will not inhibit them from standing up
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