Equine Anesthesia Flashcards
how do risks of equine anesthesia compare with other species? how do inhalable and injectable compare?
-higher mortality rate compared to other species
-inhalational 3x greater risk of death than injectable
Challenges of Equine Anesthesia
¡ Horse size and personality
¡ Control for IV access
¡ People & Equipment needs
¡ Maintenance Duration
¡ Proper positioning for surgery
¡ Recovery can be problematic
what type of anesthesia gives us better recovieries?
Maintenance with injectable anesthetics promote better recoveries with less ataxia vs. maintenance with inhalational
Specific Risks with Equine Anesthesia
¡ Injury to handler and staff
¡ Injury to horse
¡ Hypoxemia with recumbency
¡ Cardiovascular complications
¡Nasal /ocularedema
¡ Corneal ulcers
when are there risks of hypoxemia for equine anesthesia?
¡ Can develop with inhalational or field injectable anesthesia
- Dorsal recumbency > lateral recumbency
¡ Significant if on room air without supplemental oxygen
¡ Significant in dorsal recumbency in colics due to gastrointestinal distension and reduced CO
>V/Q mismatch
what are the risks of hypotension for equine anesthesia?
¡MBP <60 - 70 mmHg
¡ Very common with inhalational anesthesia
> Even with healthy horses
¡ Prolonged hypotension increases morbidity and mortality
¡ Cardiovascular support necessary under inhalational
¡ Low BP NOT an issue with field injectable induction and maintenance techniques
considerations for injury prevention with proper positions for inhalant anesthetics
§ Surgical tables
§ Thick padding required
§ Upper limbs supported in lateral
§ Thorax/ hind end supports in dorsal recumbency
considerations for injury prevention with proper positions for injectable anesthetics
§ Lateral
* Relaxed head and neck position
* Lower fore-limb forward
* Hind limbs relaxed
§ Halter & Lead-rope on
* Towel protects eyes
* Towel or other padding for rings of halter
Specific Equine Considerations for fasting before anesthesia
Withhold Food but not WATER
¡ Remove Hay; Withhold grain
¡ 4-6 hours recommended
> to reduce abdominal fill and decrease compression of the diaphragm
not concerned about aspiration pneumonia as horses do not vomit
¡ <4 week old foals do not prevent nursing > 1-2 hrs
Pre-Anesthetic Conditions Requiring Stabilization
Significant dehydration (>5%)
Blood loss
Acidemia - pH < 7.2 / Electrolyte abnormalities
Any significant disease (cardiac/respiratory/other)
Support for a significant lameness
good seadation in equine will impact dose of injectable or inhalant anesthetic how?
reduce dose
do we titrate dose of induction agent to effect in LA? why?
no, administer as injectable full dose amount
* To attain recumbency safely
* We cannot titrate to effect due to level of ataxia without full unconsciousness
* Then we focus on ET intubation and positioning
* We can handle small foals the same as small animals
preanesthetic sedation main options, and some secondary options
Main:
Xylazine
Detomidine
Romifidine
§Phenothiazines
* Acepromazine is key drug
* Given prior to sedation with alpha2-agonist
§Benzodiazepines
* Diazepam, Midazolam
* Not good sedation in standing adult horse
-in foals gives sedation
are benzodiazepines a food options for sedation in an adult horse
not, but can be used for foals
induction agents for equine anesthesia
- Propofol
- Alfaxalone
- Ketamine:Benzodiazepine
¡ Midazolam or diazepam - Mask/Tank Inhalant
- Opioid and Benzodiazepine
¡ In very critical cases
¡ ASA 4-5
¡ Will not work in healthy patient
¡ Barbiturates - not as common now
¡ Etomidate; Telazol - not available in Canada
how do we use ketamine as an induction agent
¡ Ketamine dose is mixed with Benzodiazepine dose
>not equal volume in equine
most common equine induction agent? does it have consistent results?
ketamine
¡Predictable induction and recovery for field
¡Predictable induction inhalational
Benzodiazepines are mixed with ketamine in the same syringe
effects of ketamine & diazepam or midazolam and advantages
¡Sympathomimetic effects of ketamine
>Which maintains HR, BP and CO
> This benefit can last for up to 10 minutes, while ketamine concentrations in the blood are higher
¡Smooth consistent induction
> Approximately 30 seconds for recumbency
-can use appropriate volume
disadvantages of ketamine & diazepam or midazolam
-both are scheduled drugs
what is Guaifenesin? what are its uses and effects? pros and cons?
-central acting muscle relaxant
-minimal anesthetic properties
-no resp muscle paralysis
-may cause cardiovascular depression
-no analgesia
-precipitation at room temp
-irritating; need an IV catheter
¡ Part of induction protocol when support
¡OR
¡ Maintenance with “triple drip” GKX
what is Guaifenesin? what are its uses and effects? pros and cons?
-central acting muscle relaxant
-minimal anesthetic properties
-no resp muscle paralysis
-may cause cardiovascular depression
-no analgesia
-precipitation at room temp
-irritating; need an IV catheter
¡ Part of induction protocol when support
¡OR
¡ Maintenance with “triple drip” GKX
typical options of equine induction? what are considerations? when would we not want to use one of these options?
-ketamine
-ketamine and diazepam
> 9-12 min sx time
ketamine and guaifenesin (gg)
÷GG only when can support ataxia
÷Swing gate
>GG NOT for open free Induction
what type of drug is theopental and what are its advantages as an induction agent?
Barbiturate
Advantages; cheap, short onset
disadvantages of thiopental as an induction agent
¡–ve CV effects-reduced BP, CO, arrhythmias likely
> Bigeminal rhythm – normal complex, then PVC ¡Respiratory effects-apnea, hypoventilation
¡Excitement on induction possible
¡ Irritating if given perivascular = tissue slough
¡Scheduled - records required
¡Currently low availability
¡Less optimal phase to recumbency
¡Poor recovery with greater ataxia
disadvantages of thiopental as an induction agent
¡–ve CV effects- reduced BP, CO, arrhythmias likely
> Bigeminal rhythm – normal complex, then PVC
¡Respiratory effects-apnea, hypoventilation
¡Excitement on induction possible
¡ Irritating if given perivascular = tissue slough
¡Scheduled - records required
¡Currently low availability
¡Less optimal phase to recumbency
¡Poor recovery with greater ataxia
foal <1wk anesthesia induction agent and protocol
÷Consider the age and disease
÷Sick = referral
<1 week old:
¡ Propofol, ketamine, Alfaxalone ¡ low dose, IV
Less Ideal:
¡ Mask induction
¡ Nasotracheal intubation and inhalant
Pre-anesthetic Sedation Ideal
foal 1-2wks sedation and induction
§ Diazepam or midazolam, butorphanol sedation
§ Low dose alpha2-agonist
§ Ketamine, propofol, or alfaxalone induction
foal >2wks and healthy sedation and induction protocol
§ Alpha2-agonist sedation as necessary
§ Benzodiazepine and ketamine induction
§ Propofol or alfaxalone possible too
§ Watch Temperature and resp rate
what should we be mindful of/ look out for with propofol induction of a foal?
Careful as may see:
-greater respiratory depression
-decreased PaO2
-Lower blood pressures!
>Vs. adult horse
>Vs. SA
what should we be mindful of/ look out for with propofol induction of a foal?
Careful as may see:
-greater respiratory depression
-decreased PaO2
-Lower blood pressures!
>Vs. adult horse
>Vs. SA
induction process, general
- Assess Sedation level; Attain IV access; Equipment prepared
- Assess cardiorespiratory status
*HR, RR, MM colour, CRT
*Monitors and pre-oxygenation possible in foals - Give FULL induction dose all at once
*Support case to positioning in lateral recumbency
*For field injectable anesthesia – once positioned, start surgery – no ET tube - Perform ET intubation and cuff inflation, transfer to inhalant/maintenance anesthesia and permit further positioning and padding for the procedure
free induction safety measures and positioning
¡ Person on the head > Supporting
¡ Person on the tail (optional)
>Wait 30 sec before grab tail
=> ↓CO from sedation
=> Note this time
> Pull straight back
¡ Pull to preferred lateral
techniqe for ET intubation in euquine? when do we use/ not use?
Blind technique
Placed for inhalational
Not used with injectable and short procedures
ET tubes expensive >Mouth gag
inhalant anesthesia maintenance drugs and safety considerations? Risks?
¡Isoflurane, Sevoflurane
¡↑ morbidity and mortality with sx time ≥ 4 hrs
>And in sick animals
Risks:
¡ localized / generalized myopathy
¡ neuropathy
¡ hypotension
¡ hypoxemia
¡ recovery excitement +/- injury
¡ Partial IV anesthesia (PIVA)
maintenance phase consideration for field anesthesia? how do we do it? risks?
To prolong surgery time up to 30 min:
> Additional xylazine /ketamine mixed together given IV
>30-50% of each initial dose
>give every 5 min of surgery time based on monitoring signs
Injectable anesthesia > 45min to 1 hour:
¡ increased risks
¡ Worsens recovery from > ataxia
¡ Watch your time
¡ Hypoxemia develops and more significant with prolonged times
what is the use of a triple drip mixture? what is in it? considerations?
For Maintenance of GA
-GG bag
>add xylazine or romifidine or detomidine
and
>ketamine
-administer IV
-careful monitoring of depth
-poor recoveries if >60min
cardiovascular effects of propofol (HR, CO, contractility, SVR, BP, arrrythmia potential)
HR: +/- down
CO: down
contractility: down
SVR: very down
BP: very down
arrhythmia potenital: +
cardiovascular effects of GG (HR, CO, contractility, SVR, BP, arrrythmia potential)
HR: -
CO: down?
contractility: down?
SVR: down?
BP: very down?
arrhythmia potenital: -
cardiovascular effects of ketamine & diazepam or medazolam (HR, CO, contractility, SVR, BP, arrrythmia potential)
HR: NC or up
CO: up, NC, or down (related to symp tone)
contractility: up, NC, or down (related to symp tone and stores, sickness of petient)
SVR: NC
BP: NC or up, maybe down in sick
arrhythmia potenital: ++ mostly if high rate produced
cardiovascular effects of inhalant anesthetics (HR, CO, contractility, SVR, BP, arrrythmia potential)
HR: NC +/- down
CO: super down
contractility: super down
SVR: very down
BP: super down
arrhythmia potenital: less with iso and sevo than older older agents
resp effects of propofol (RR, TV, incidence of apnea, ventilatory pattern)
RR: down
TV: down
incidence of apnea: ++
ventilatory pattern: apnea with fast inj.
resp effects of GG (RR, TV, incidence of apnea, ventilatory pattern)
RR: down
TV: down
incidence of apnea: possible from depth. Does not paralyze diaphragm
ventilatory pattern: -
resp effects of ketamine/BZD (RR, TV, incidence of apnea, ventilatory pattern)
RR: NC or down
TV: NC
incidence of apnea: +
ventilatory pattern: apneustic, irregular
resp effects of inhalants (RR, TV, incidence of apnea, ventilatory pattern)
RR: super down with high depth apnea
TV: very down
incidence of apnea: ++ increased depth causes apnea which is protective
ventilatory pattern: shallow and poor with increased depth
what should we monitor while horse in under anesthetic?
Eyes
* Position
* Reflexes
* Tearing
* Nystagmus
§ Muscle tone, movement
* Ears, tongue, eyelids
* Tail, neck, legs
§ Cardio-respiratory parameters
how much time should we give for equine recovery phase?
¡Do not rush it
¡Ideal 20 min field
¡Ideal 1 hr inhalational
¡Sedation in recovery for inhalational
what should we give for recovery from inhalational anesthetic?
sedation
positioning for equine recovery
want a sternal phase
methods of equine recovery dependant on:
¡Type of anesthesia
¡Time down
¡Surgery (fracture/colic)
¡Personality of horse
¡Facility you have
what should be allowed to move in sternal phase of recovery after injectable anesthetic? what will the process look like?
head
-should be free recovery, can have a person on halter rope if wanted but dont try to restrict movement
>be patient and encourage only when appropriate
what should the recovery after inhlalational anesthetic look like? what safety precatiouns should we make?
¡Free – alone in stall
¡ Padded room/floor
¡ Post-Inhalant
> Horse sedated > Xylazine and acepromazine
when should we extubate a horse?
When swallowing
* If you can safely remain in
recovery stall with horse while lateral
OR
§ When standing
