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ANESTHESIA - 2 > 28 – Equine Field Anesthesia > Flashcards

28 – Equine Field Anesthesia Flashcards

1
Q

What are 5 considerations for field anesthesia?

A
  1. Procedural
  2. Environmental
  3. Patient
  4. Equipment
  5. Personnel
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2
Q

Procedural considerations

A
  • Nature of injury?
  • Standing sedation and local block OR general anesthesia?
  • Complexity of surgery?
  • Expected duration?
    o Top ups
    o Triple drip: combo of drugs, longer duration and action (medicine will accumulate and contribute to ‘rough’ recovery)
  • *only SIMPLE procedures of SHORT DURATION should be attempted away from the ‘relative safety’ of well-equipped and well-staffed hospital
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3
Q

What are the optimal environmental conditions?

A
  • Soft ground
  • Flat or gentle gradient
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4
Q

What should be avoided for environmental conditions?

A
  • Man made or natural hazards
    o Barbed wires fences
    o Farm equipment
    o Ponds
    o Streams
    o Ravines
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5
Q

What are the 4 points for patient considerations?

A
  1. Thorough history and physical examination
  2. Stabilization
  3. Weight estimation
  4. Owner consent
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6
Q

Thorough history and physical examination (patient considerations)

A
  • CV and respiratory systems
  • Gut motility
  • Pain
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7
Q

Stabilization (patient considerations)

A
  • Hemorrhage
  • Fasting (minimum 6 hrs)
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8
Q

Weight estimation (patient considerations)

A
  • *Drug dosages require an accurate weight
  • Tape
  • Calculation
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9
Q

What is the MINIMUM anesthesia equipment?

A
  • IV catheters
  • sufficient amount of drugs
  • soft ropes with an appropriate halter
  • small towels: covering/protecting eyes
  • Oxygen supplementation
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10
Q

Oxygen supplementation

A
  • Horses very prone to hypoxemia during GA (V/Q MISMATCH!)
  • E-tank with nasal insufflation
    o Full E-tank (2200psi) holds 625L of O2
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11
Q

Personnel considerations

A
  • You are responsible for safety of the horse, but ALSO safety of owner and every other individual!
  • *wide range
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12
Q

What are some sedation/premedication’s for horses?

A
  1. Acepromazine
  2. Alpha2 agonists
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13
Q

Acepromazine (sedation/premedication)

A
  • Useful as ‘pre-med’ often in combo with other drugs
  • Used alone for non-painful procedures
  • Sufficient time should be allowed for it to work (*30-40min)
  • Provides ANTI-ARRHYTHMIC EFFECT
  • Vasodilation and hypotension does occur (alpha1 antagonism)
  • Penile prolapse! (AVOID IN BREEDING STALLIONS)
  • Use to decrease mare’s stress if working on the foal
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14
Q

Alpha2 agonists (sedation/premedication)

A
  • MORE reliable sedation
  • Analgesia and muscle relaxation (some ataxia)
  • *equipotent doses of 3 different alpha2 agonists used in horses
  • *DO NOT USE TRUST WHEN USED ALONE=HORSES CAN STILL KICK
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15
Q

What are the 3 alpha2 agonists used in horses?

A
  • Xylazine (20 mins)
  • Detomidine (40 mins)
  • Romifidine (40 mins)
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16
Q

Standing sedation vs pre-anesthetic medication doses of alpha2 agonists

A
  • Standing: low dose
  • Pre-anesthetic medication: high dose
17
Q

Alpha2 agonists have CV effects with IV administration

A
  • Bradycardia does NOT require Atropine in horses and ruminants
    o Wait a few minutes and HR will increase (need high enough HR to get ketamine to brain to have a SMOOTH induction)
  • Also don’t use atropine in horses and ruminants as it decreases GI motility
  • *do not titrate in large animals=by pass excitement phase
18
Q

Alpha2 agonists with opioids

A
  • *butorphanol
  • Morphine: use a longer lasting alpha2 agonist
  • *can mix drugs OR give drugs separately
  • *want to use sedative with opioids as they can cause excitement
19
Q

Alpha2 agonists with opioids and acepromazine

A
  • COMMON=Detomidine/butorphanol/acepromazine
  • Detomidine/acepromazine is good for MARES
20
Q

What happens with romifidine mixed with acepromazine?

A
  • Precipitation=do NOT administer
21
Q

Induction of anesthesia: 6 steps

A
  1. Pre-anesthetic preparation
  2. Assess facilities/environment
  3. Place an IV catheter
  4. Check halter and ropes (thicker banded are better)
  5. Protect facial nerve if leaving halter on head
  6. Select site: brief the help on safety and potential problems
22
Q

Pre-anesthetic preparation

A
  • Fast minimum 6 hours; water until 1 hr before
  • Medical history
  • Physical examination
  • Clinical haematology as necessary
23
Q

What are the common anesthetic field induction protocols?

A
  • Xylazine (1mg/kg IV) OR detomidine (10-20 micrograms/kg IV)
  • *wait a few minutes for peak sedation
  • Mix: diazepam and ketamine
    o Diazepam: optional but does ‘smooth’ induction
  • Can add butorphanol
  • Consider local anesthetic techniques
24
Q

What do you need to do ensure before using Ketamine to induce?

A
  • ‘nose to knees’ sedation!
    o If poor=top up sedation with alpha 2 agonist
  • Check HR
    o If extremely low=wait until it comes back up (2-3mins)
25
Q

Things to consider with recumbency?

A
  • Don’t allow head to smack ground
  • Check vital signs and anesthetic depth
  • Position for procedure
  • Protect eyes
  • Proteins cranial nerves: remove halter
26
Q

What are the 2 options for maintenance of anesthesia?

A
  1. Incremental top-up IV bolus
  2. Continuous IV infusions
27
Q

What is a ‘top-up’ for maintenance of anesthesia?

A
  • Ketamine + xylazine
    o Mix 1/3 to1/2 the pre-medication and induction doses
    o May provide 2-3 ‘top ups’
    o Given every 10-15 mins depending on depth of anesthesia
  • *ketamine is slightly cumulative
    o After 3rd ‘top up’ dosing interval should be increased OR subsequent doses decreased
28
Q

When would you use ‘triple-drip’ in maintenance of anesthesia?

A
  • When need a little longer duration of anesthetic time
  • Max anesthesia time=~90mins
29
Q

How do you prepare and use a ‘triple drip’?

A
  • In 1L 5% guaifenesin add
    o 500mg Xylazine
    o 1000 mg Ketamine
  • Rate of 2ml/kg/hr
  • Good for procedures up to 60mins
    o Ideally with Oxygen and good positioning
  • Cardiopulmonary stability
  • Good analgesia
  • Easy to use
  • Good recovery
30
Q

What are the ways the check the depth of anesthesia?

A
  • Pulse quality, mucous membrane colour, CRT, HR
  • RR and depth
  • Check eye reflexes: palpebral reflex is ‘brisk’
  • *do NOT use corneal reflexes=CAUSES TRAUMA TO EYE
  • Horses eyes stay central
31
Q

What do you see in a horse that is in a ‘LIGHT’ plane of anesthesia?

A
  • Spontaneous blinking
  • Tearing
  • Nystagmus: *good indicator they are deep enough and also that they are going to wake up
32
Q

What are some things used for monitoring in the field?

A
  • Portable equipment
  • Measure BP with doppler and sphygmomanometer (ex. on tail)
  • Use pulse oximeter
33
Q

What is some life support examples?

A
  • If longer procedure, consider
    o Oxygen
    o Fluids
  • *refer long procedures
34
Q

Recovery

A
  • Usually don’t use reversal
  • Control recovery: ‘hold’ tail to help them be more stabilized
  • Keep safety of people in mind
  • Avoid noise
  • Keep eyes covered
  • Consider sedation (xylazine) if recent ‘top-up’ with ketamine alone in previous 10mins
  • *if longer procedure: consider placing a urinary catheter and emptying the bladder
35
Q

What are the 3 drug categories used in horses for analgesia?

A
  • NSAIDs
  • Opioids
  • Local anesthetic block
36
Q

NSAIDs for analgesia

A
  • Used pre-emptively to minimize surgical/inflammation pain
37
Q

Opioids for analgesia

A
  • Provides good analgesia and INCREASE sedation
    o Butorphanol: 60-90mins
    o Morphine: 2-4 hrs
    o Buprenorphine: 12 hrs, but 30-45min onset
38
Q

Local anesthetic blocks for analgesia

A
  • Useful part of balanced analgesia
  • Ex. Intra-testicular for castration

ANESTHESIA - 2 (15 decks)

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