HORSE anesthesia – Flashcards
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Why is a horse considered to be a high anesthetic risk patient?
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1% of them die Therefore we should avoid it if possible
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Before considering putting a horse anesthesia, what should we do
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warn the owner of the risks
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What are the major risk factors of anesthesia in horses?
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increased duration of anesthesia Time operation is carries out
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In terms of anesthetic risk in horses, what is the anesthetic risk difference of isofluane and haloflurane?
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no difference
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What drug can you give to half the anesthetic death rate?
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acepromazine
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What drug can you give to cause a slight increase in the anesthetic death rate?
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romifidine without acepromazine
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When do emergencies show during anesthesia in horses?
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induction and during maintenance
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What emergencies occur during the immediate recovery period in horses? (3)
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airway obstruction, physical damage, myopathy
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When are the 3 periods emergencies usually occur for horse sx?
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during anesthesia During the immediate recovery period Over the next few days
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What emergencies occur during over the next few days after anesthesia?
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resultant physical problems, post-op colic
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A standing sedation in a horse needs the additional use of what?
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local analgesia >> including infiltration and specific blocks
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Why may field anesthesia in horses be safer?
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because you can only sedate them for short procedures
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What equipment should be available for field anesthesia in horses, despite that the anesthesia is often done with no means of supplementing oxygen or providing IPPV?
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ET tube, oxygen cylinder, Hudson valve
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How do we anesthetize a horse in a field?
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repeated bolus injections OR infusion >> TIVA
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How do we anesthetize a horse in a surgical suite?
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inhalational anestion TIVA with oxygen and ventilator support
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When is it ok to send a horse for meat slaughter after giving chloroform?
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NEVER
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What are the common cardiac abnormalities found in a pre-anesthetic exam of a horse?
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arrhythmias and murmurs
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What is the common respiratory dz of the horse found in a pre-anesthetic exam of a horse?
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COPD (RAD)
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3 things that may leads to a tachyarrhythmia in a horse?
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toxemia Blood loss Cardiac failure
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2 things that may cause a bradyarrhythmia in a horse?
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second degree heart block Atrial fibrillation
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You must differentiate atrial fibrillation from
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2nd degree block
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If you see an atrial fibrillation in a horse, what should you check for?
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signs of cardiac failure
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If a horse has an atrial fibrillation and the owner still wants surgery, what medical management can be done to lessen the risk of surgery?
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send home after quinidine Or consider electroconversion
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Why drug makes atrial fibrillation worse and why?
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a2 agonists >> cause bradycardia
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How can you determine the significance of a murmur in a horse?
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exercise intolerance Physical signs of cardiac failure (like a jugular pulse)
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What age do horses get COPD?
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older ones
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What causes COPD in horses? What are the cx?
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sensitization to allergens like hay/straw Resulting airway obstruction, HEAVE line as a sign of chronic expiratory effort, "snotty nose"
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Prior to an emergency colic surgery, what tests are done and why?
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hematology and biochemistry Evaluate for hypovolemia and endotoxemia
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Are pre-anesthetic blood tests done prior to routine elective surgery in horses?
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not in most clinics
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How does the level of fitness in a horse affect anesthesia
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fitter horses are harder to anesthestize
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(smaller/heavier) horses are at a higher risk of problems
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heavier `~MINIMUM amount to starve a horse before surgery?@2 hours
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How do you best avoid 'bloat' in a horse?
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don't give them good grass to eat beforehand
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Prolonged use of a2 agonists can cause _ in a horse
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ileus
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What is the ideal time for a horse to starve for a prolonged anesthesia?
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8-12 hours in order to ensure an empty stomach
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When is it ok to compromise the 8-12 hr fasting window for horses?
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short anesthesia
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Even for sedation, a2's _ gut motility
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reduce
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Peri-operative analgesics in horses (6)
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NSAIDs Opioids Ketamine A2 agonists Local analgesics Epidural analgesia
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NSAID toxicity in horses typically manifests as
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colitis/diarrhea --> death
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When is an NSAID an excellent peri-operative analgesic to use in a horse
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where pain is caused by inflammation
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Why is it very important to not exceed the stated dose of NSAIDs in a horse?
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toxic!! >> damage the blood vessels in the gut
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Route of administration of meperidine? Why?
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IM only Anaphylactoid type reactions IV
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NB of using fentanyl as a peri-operative analgesic in horses?
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questionable effects on the MAC of subsequent anesthesia
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List the opioids used in horses (7)
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morphine Methadone Meperidine (IM only) Fentanyl Butorphanol Buprenorphine Hydromorphan
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PROS of opioid use in horses (3)
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1. Effective and essential pre-emptive analgesia 2. Effective and essential analgesic agents 3. Effective (slow onset) given by epidural injection
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CONS of opioid use in horses (3)
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1. Overdose in unsedated horses may cause excitement and stereotypic behavior 2. Repeated doses impair GI motility 3. Occasional pruritus with epidural
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Intra-operative opioids in horses do NOT significantly reduce the MAC of _
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inhalation agents
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Intra-operative opioids in horses are effective in _ anesthesia
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stabilizing
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Local analgesia in horses is used for which procedures (4)
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total analgesia Castration Very specific limb blocks Caudal and lumbar epidural
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What classes of drugs are used for caudal and lumbar epidurals in horses?
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a2's and opioids
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What is the most important aspect of doing a caudal/lumbar epidural in a horses?
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recovery >> need to be able to stand up without breaking a leg
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What is the most important aspect of doing a specific limb block in a horse?
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recovery >> need to be able to stand up without breaking a leg
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When is IV catheterizaion in a horse necessary?
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standing sedation and general anesthesia
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Where are IV catheters placed in horses?
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jugular
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What direction do you place your IV cather in the horse jugular?
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either towards the head or the heart but both have complications
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If a cather is pointing downwards in the jugular v, what is the biggest risk?
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air embolism
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You placed a catheter is a jugular v of a horse, but the horse when down before you ended giving the injection, what happened?
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You actually put the catheter intracarotoid
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Risk of having a 'long stay' catheter
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infection
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When do you increase your risk of jugular thrombosis in the horse with a catheter? (2)
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guaifenesin >> DRUG IRRITATION Endotoxemia
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How does the flight or fight response f up your sedation?
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high levels of circulating epinephrine/norepinephrine >> no animal which is severely distressed or upset will sedate
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4 rules to achieve good sedation
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never trust the result or you'll get kicked Don't expect too much Have animal calm at the start Give adequate time for effect
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Why should you never expect too much out of a sedative?
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sedative =/= general anesthetic
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What are the ways of giving a sedative to a horse?
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IM, IV, possibly oral
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Premedication drug routine for a horse?
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acepromazine bc its long acting and can reduce deaths Then followed by a2 agonist/butorphanol (or some other opioid)
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Why is acepromazine routinely given as a pre-anesthesthetic in horses (4)
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*reduced mortallity >> 50% reduction!!!!* Potentially improved recoveries Potential MAC reduction
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How long should you expect BP to be depressed with ace in horses
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6-8 hours
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Why is ace a risk in stallions?
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penile relaxation or priapism
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What drug has the more obvious sedative effect: acepromazine or a2 agonists?
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s2 agonists
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Effectof acepromazine on the GIT
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antispasmodic
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Duration of effect of acepromazine
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long acting
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What is the least effective (but still works) route of administration of acepromazine?
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ora
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Onset of action of acepromazine as a mood tranquilizer
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about 20 minutes Needs time to effect
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uses of acepromazine (3)
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to calm the frightened or apprehensive animal Training (for showing, boxing, etc) Premedication
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What a2 aggonists are used for sedation in the horse (4)
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xylazine Detmidine Romifidine Kinda sometimes medetomidine
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When is kicking not a risk in the sedated horse?
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even deeply sedated horses respond to toucg and may kick They even kick when they're dead wtf
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a2 agonists in horses are routinely combined with what drug for horse sedation?
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butorphanol But any opioid choice is ok
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Weird side effect of horses on butorphanol
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twitches from opioid excitement
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What is the most important thing about sedating feisty/unmanageable horses?
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TIME >> drug effects are very unpredictable in stress/excited horses
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2 oral sedatives for the feisty/unmanageable horse?
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ACP Detomidine
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How long does it take for the peak effect of an IM injection of a sedative in a horse?
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30 minutes
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Why would you give a feisty horse an oral sedation?
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so you can give a drug IM or IV after using the oral and fully sedate the horse to your wanted level
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List the a2 agonists by a2 selectivity?
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medetomidine > detomidine, romifidine > xylazine
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List the a2 agonists by duration of action
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romifidine > detomidine > medetomidine > xylazine
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Which a2 agonist makes hoses less ataxic and why?
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romifidine >> less mm relaxant effects
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Which a2 agonists provide the best analgesia?
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xylazine, medetomidine
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Which a2 agonists can be given by infusio (3)?
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detomidine, xylazine, medetomidine
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Why does detmodine have an advantage for IM use?
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volume
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What drugs are given for a 'standing' sedated surgery in a horse?
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xylazine or detomidine plus an opioid
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When is physical damage most likely to occur to either the horse or handlers during general anesthesia in the horse?
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induction and recovery
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Common problems with general anesthesia in the horse (5)
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physical damage Cardiac arrest Hypoxia Hypercarbia Post-op complications
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What are the post-op complications that occur from horse general anesthesia (3)
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myopathy Neuropathy Spinal damage
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How is anesthetic induction in ADULT horses physically accomplished?
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*ALWAYS intravenous*
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Induction combinations for general anesthesia in the horse are all given after
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ACP premed
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Induction combinations used for general anesthesia in the horse (4)
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a2/ketamine +/- benzodiazepine A2/guaifenesin/ketamine A2 and/or ACP plus thiopental Guaifenesin/thiopental or ketamine
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BEFORE giving ketamine to the horse?
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ensure the horse is well sedated!
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NEVER give what drug BEFORE ketamine?
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a2 agonist
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Why is it so dangerous for humans to be working with horse doses of ketamine?
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absorbed across muscous mmembranes so dont get it in your face/eyes
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T/F Guaifenesis is an anesthetic
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False, guaifenesin is NOT an anesthetic
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Drug properties of guiaifenesin that make it worthwhile for us to use
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centrally acting muscle relaxant with some sedative properties
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What phases of anesthesia is guaifenesin used for?
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induction and maintenance
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Guaifenesin is made up from
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crystals or stabilized solutions
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Why do you need to dilute guaifenesin? What concentration is it diluted to?
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5% Causes hemolysis, phlebitis
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What route must you give guaifenesin and why?
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irritant if injected perivascularly
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What items are required if you're going to use guaifenesin in a horse?
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assistants and a 'crush'
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What things help you control the fall of the horse during general anesthetic induction?
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free fall Tilting table Gate
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Whyis it so easy to intubate a horse? What method is used?
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weak laryngeal reflexes "blind" method of intubation is used
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Why is it so important that cuffs are not leaky in an ET tube (2)?
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cant keep the reservoir bag Reguritation with colics
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What methods can be employed for anesthetic maintenance of general anesthesia in the horse?
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long term TIVA Short term TIVA Inhalation PIVA (partial intravenous anesthesia
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What is the biggest limiting factor of field anesthesia
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time >> cant keep the horse down too long
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Induction method used in field anesthesia
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any!
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What are the minimal standards necessary if you are going to do field anesthesia?
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monitoring devices Maybe oxygen source ET tube Ability to ventilate
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What is probably the best drug combo to use for field anesthesia and why (5)
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a2 agonist/ketamine Good quality induuction Minimal cardiopulmonary depression High safety margin Can top up or infuse to prolong Excellent recovery
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a2 agonists/ketamine in field anesthesia make for an excellent recovery especially if no _ is used
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benzodiazepine
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What is the limiting factor of "topping-up" field anesthesia?
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amount of ketamine needed
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Combination of using 2 different types of drugs to maintain field anesthesia through 'top-ups' results in _ effects
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synergistic
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What 2 things can you use to 'top-up' field anesthesia
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original drugs used for induction Triple drip
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Top-up drug combinations for field anesthesia in horses (3)
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a2 agonist/ketamine Thiopental Ketamine-midazolam
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If you use thiopental to top-up field anesthesia in a horse, what is the drawback?
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will impair recovery if used repeatedly
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If topping-up field anesthesia with ketamine-midazolam, giving too much midazolam will
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give a poor recovery If toppinng up field anesthesia with an a2 agonsist/ketamine combo, it is important that you@limit the xylazine
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What drugs are in the triple drip
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guaifenesin, a2 agonist (like xylazine), and ketamine
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How long does TIVA for field anesthesia give good stable anesthesia
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short procedures >> ideally up to 1 hour
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Triple drip is best used after no _ at induction
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no guaifenesin at induction Then you can move on to triple drip
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SPECIFIC TO TRIPLE DRIP: when monitoring horses under triple drip TIVA, they appear
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"light" Strong palpebral reflex, lacrimation, swallowing, vocalization
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Why is it best to use a local anesthetic when using triple trip TIVA?
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horses still maintain gentle, purposeful responses to surgical stimulation so you use a local to prevent that
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You see "paradoxical" signs during a triple drip anesthesia, what are they? What is happening?
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rigid limbs, opithotonus OVERDOSE!
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How is it best to maintain prolonged anesthesia? Why?
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use both inhalation with TIVA infusion Reduces the MAC
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Common problems during horse general anesthesia?
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hypotension Hypoxia from being in dorsal recumbency Hypercapnia Cardiac arrest Post-operative complications like myopathy, neuropathy, spinal damage
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Although horses can get sudden cardiac arrest for no reason during general anesthesia, what is sometimes the warning sign?
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bradycardia
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Because horses are so large, what anesthetic system do you use?
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close system with minimum flow rates oxygen consumption
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FGF rate for a horse under anesthesia?
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5ml/kg/min
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What halogenated inhalation agents are used in horses?
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isoflurance Sevoflurane Desflurane
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Because horses are not designed for prolonged recumbency, you must
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support the limbs!
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During any general horse anesthesia, what are the basic guidelines you should follow in order to prevent complications (4)
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place plenty of eye lube Support the limbs! Optimize ventilation Catheterize bladder
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How should you place a horse in lateral recumbency during general anesthesia? What do you do wwith the front leg? Hind leg? Upper limbs? Head?
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everything very padded with soft pads UNDER front leg down forward UNDER hind leg pull back DON'T have the upper legs across the abdomen Upper limbs should be supported Head slightly raised
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Why should there be no sharp edges that your horse is laying on during general anesthesia?
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don't want nerve damage, esp the facial n
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Why should horse upper legs not be pulled across the abdomen?
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blocks venous return and leads to upper limb myopathy
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If a horse is in dorsal recumbency, what should should NOT do to the hind legs?
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do NOT extend the hind legs and lock the stifles Muscle and nerve damage will occur
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If the horse is in any position during anesthesia, why is it important to not overstretch the head/neck? When is the overstretching most likely to happen?
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can get laryngeal paralysis More likely to happen during dorsal recumbency
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When a horse is waking up from a volatile anesthetic, what should always be on hand and why?
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and IV agent because wake-up can be violent
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In what types of horses is it more difficult to maintain a stable plane of anesthesia?
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fit or 'stressed' horses
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Why are the adjustments in anesthetic depth of horses, so slow?
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very large system But this is becoming less of a problem with new inhalation agents
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Despite your monitoring, why is it difficult to maintain the appropriate anesthetic depth in horses?
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harder to assess depth of anesthesia in horses
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There is often no sign the horse needs intra-op analgesia until?
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until the horse moves then there is an appropriate CV change
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Methods of intra-op analgesia in horses (4)
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Local blocks More inhalation "top ups" = small doses of ketamine or thiopental Partial intravenous anesthesia
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What is the best method of analgesia to use intra-operatively in a horse and why?
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local block because this way they can't kick you with an intact spinal reflex
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When during anesthesia can NSAIDs be used?
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provide post-op analgesia NO effect intra-operatively
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PIVA drugs for intra-operative analgesia (4)
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ketamine infusion More a2 agonist Bolus doses or infusion Lidocaine infusion
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Why are opioids as intra-operative analgesics in horses not always usesful?
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can cause movement (and therefore make things worse) even under anesthesia'
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When using lidocaine CRI as an intra-op analgesic in horses, when should you stop it? Why?
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stop 20 minutes before end of anesthesia or you'll have a poor recovery
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Pros of using ketamine as an intra-op analgesia? Con?
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PROS = more effective and the only one that actually improve SV status CON = poor recovery if give too much
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When is using direct measurement of arterial BP essential?
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if using a volatile agent
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What monitoring equipment should you have if a horse is anesthetized with a volatile agent?
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capnography Blood gas analysis Pulse ox End tidal agent monitor
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Which inhalation agents cause a drop in BP in the horse?
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all of them!
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Which inhalation agent causes the worst myocardial depression?
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halothane
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Which inhalation agent causes the worst vasodilation?
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isoflurane
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What 2 things result in a low cardiac output?
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myocardial depression and a low HR
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Pathogenesis of how vasoconstriction is bad for the heart and tissues?
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vasoconstriction >> high total peripheral resistance >> greater cardiac work >> fall in cardiac output >> poor peripheral perfusion
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Danger of severe hypotension in the horse? Moderate and prolonged?
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severe - cardiac arrest Moderate and prolonged - myopathy
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Hypotension in the horse during surgery has a contribution to what post-op event?
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poor gut blood flow >> post-op colic
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TQ what drug can be given to improve cardiac output (bad cause by hypotension)
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a positive inotrope like *dobutamine* Or ephedrine
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How should you NOT treat hypotension unless *very very severe*
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do not give drugs to vaso-constrict like phenylephrine
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Tx of anesthetic hypotension? (3)
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1. Give + inotropes like dobutamine 2. reduce volatile gas 3. give fluids
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Why is hypoventilation bad? (2)
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causes *hypercapnia* Prevent uptake of isoflurane/sevoflurane
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How can you counteract hypoventilation?
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IPPV Or reduce FiO2
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Why is hypercapnia not always a problem (within reason)
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it can be a good circulatory stimulant and improve CO
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Cx of very high levels of CO2?
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neck tremors Horse looks like its waking
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What is the level of CO2 where you start to see neck tremors?
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>90 mmHg
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T/F Hypoxemia is synonymous with respiratory depression?
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FALSE Hypoxemia =/= respiratory depression
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What horse is most prone to hypoxemia?
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large round bodied horses in dorsal recumbency
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Why do anesthetized horses become hypoxemia (2)
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shunt V/Q mismatch
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V/Q mismatch is a form of
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*SHUNT*
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Define ventilation/perfusion mismatch
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some areas of the lung are well ventilated but have poor perfusion OR Other areas have good perfusion but poor ventilation
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Tx of hypoxemia during inhalational anesthesia? Which tx is the best?
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IPPV using 100% oxygen Bronchodilator like albuterol Improve cardiac output to improve oxygen delivery >> best tx
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What is the best way to detect cardiac arrest in the horse caused by anesthesia? Why?
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electric monitoring Horses go on breathing for a long time after the heart stops
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Why is it so important to monitor the horse for cardiac arrest?
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it's not uncommon and the success rate of resuscitation is excellent if instituted in time
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Possible reasons a horse may go into cardiac arrest during general anesthesia (2)
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high vagal tone Severe hypotension
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Why is a defibrillator not required during cardiac arrest of a horse?
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heart almost always stops in asystole
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If a surgery may cause a vagal reflex in a horse, what do you do?
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give an anti-cholinergic in order to prevent cardiac arrest from a high vagal tone
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How does severe hypotension cause cardiac arrest
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heart is inadequately perfused
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Tx of an anesthestized horse in cardiac arrest
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swich off volatile agent IPPV with 100% oxygen External cardiac massage
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When do you give epinephrine IV or atropine IV to a horse in cardiac arrest?
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once you have obtained circulation
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How do you do an external cardiac massage?
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put the horse in lateral with the front legs forward and jump on the heart landing on knees
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With xylazine or metomidine in your prolonged anesthesia, at the end of anesthesia it is not necessary to
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reverse
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What 2 different solutions might you used if you want to prolong anesthestia with TIVA beyond the triple drip?
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reversible anesthesia (benzo, opioid, a2) Propofol based technique
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Propofol based techniques of prolonging anesthesia beyond triple drip with TIVA
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propofol/ketamine Propofol/a2 Propofol/a2/ketamine
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T/F If you're prolonging anesthesia beyond a triple drip you still need oxygen
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TRUE
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Extending anesthesia beyond a triple drip with TIVA with a propofol based technique still requires what?
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analgesia And oxygen
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What is partial intravenous anesthesia?
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intravenous infusions used to supplement inhalational anesthesia
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Drugs used in PIVA
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lidocaine Ketamine Medetomine
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Effect of lidocaine on CV status?
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probably not improved
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Why would you use lidocaine IV intra-operatively
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reduces MAC of volatile
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What kind of surgery is lidocaine an ideal analgesic *post-operatively* and why?
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post-colic surgery analgesic Positive effects on gut motility
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What are the major problems during anesthetic recovery of the horse? (3)
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airway obstruction Hypoxia Physical damage from a poor quality recovery
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How can you provide comfort to the horse during recovery (2)
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analgesia Empty bladder
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In order to maintain the airway during recovery, how can you reduced swelling?
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phenylephrine nasal drops
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How can you assist in the anesthetic recovery of the horse?
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give oxygen Maintain airway Maybe sedate a little and/or assist recovery
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How fast should a horse get up during recovery? Why?
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should get up in their own time Too fast = ataxia and increased risk of injury Too slow = increased risk of muscle damage and exhaustion
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How fast is too rapid a recovery?
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<30 minutes
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How slow is too slow a recovery?
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>2 hours
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Quality of recovery depends on (3)
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temperament of the horse Recovery assistance Drugs used for sedation/inhalation/intravenous
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Types of assisted recoveries for a horse (2)
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ropes head and tail Swimming pools
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Problems showing during or after recovery are mainly due to
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prolonged anesthesia
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Common problems showing during or after recovery (6)
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injury Nasal edema and respiratory obstruction Myopathy Neurapraxia and neuropathy Pulmonary edema Myelomalacia
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What nerves commonly get neuropathies during anesthetic recovery?
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facial n Femoral n
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What injuries commonly occur during or after anesthetic recovery?
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corneal abrasions, fractures
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How can myopathy be avoided (4)
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short surgery! Careful positioning and passing Adequate BP Good cardiac output
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What myopathies happen during anesthetic recovery? What is this due to?
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re-perfusion injury Compartmental syndrome Due to lack of perfusion of mm during sx
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Treatment of post-anesthetic myositis
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analgesics Fluids DMSO as a free radical scavenger Tender loving care : )
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Why do you give fluids to tx myositis?
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prevent renal damage from free myoglobin
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What analgesics do you give a horse with post-operative myositis?
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one dose of an NSAID Opioid plus ACP
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What happens if you don't give ACP with an opioid in a post-anesthetic horse?
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they box walk
