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Anesthesiology > Equine anesthesia seminar > Flashcards

Equine anesthesia seminar Flashcards

1
Q

Different horse breeds require different doses of

A

anesthetics

Their physiology can be very different. E.g. an arabian will require way more sedatives than a draft horse due to differences in metabolism!

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2
Q

Main goals for an anesthesiologist: (6)

A

To determine that the patient is healthy enough for the anaesthesia

Smooth induction

Stable anaesthesia

Smooth recovery

Good pain management

No complications during a post anaesthtic period

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3
Q

Anesthesia related mortality risk for horses is

A

0,9%

less during elective surgeries
emergency laparotomies between 2 – 10%

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4
Q

Higher equine anesthesia risk groups: (4)

A

Foals under 2 weeks

Horses older than 14 years

Hemodynamically compromised patients – e.g. colic surgeries

Long general anesthesia – >90 min = higher risk of myopathy

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5
Q

Pre-anesthetic evaluation of an equine patient (5)

A

Thorough anamnesis
Weight of the horse

Good clinical examination (Especially cardio-vascular and respiratory system)

Blood work – depending on a patient (for simple sedations not always but at minimum is best to check inflammatory markers and renal function)

Vaccinations – TETANUS! very important. If missing, vaccinate them. Good for vax to have been done within 6m of surgery.

Inform the owner of the risks and ask them to sign for consent.

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6
Q

How to take an equine patient weight

A

Use a scale if available.

If an equine scale is not available you may measure the horse’s chest girth and body length and calculate a weight estimate. There are also specific measuring tapes with weight estimates.

formula –> weight (kg) = (girth (cm)2 × length (cm))/ 10 815

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7
Q

Average horse weight

A

average warmblood 500-600kg
draft horse 700-800 kg
adult shetland pony 200 kg

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8
Q

Pre-anesthetic evaluations:
Cardiovascular findings and how they contribute to anesthesia risks? (2)

A

Heart auscultation
murmurs – not always a problem
arrythmias – almost always cause some difficulties

If the horse tolerates exercise, there are no edemas, jugular veins fill up nicely - the risk should be acceptable.

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9
Q

Pre-anesthetic evaluations:
respiratory system

A

Auscultate the lungs and trachea
Check for any discharge from the nose

Ask for resp. history – RAO, laryngeal hemiplegia etc.

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10
Q

When to postpone elective surgery?

A

Pyrexic
Respiratory disease
Arrythmias
Anaemic

Diarrhea
Cachexic
Neurological deficiencies
Pregnant

Bad weather (some surgery is done in teh field)
No suitable conditions

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11
Q

Preparing equine endotracheal tubes

A

always use the largest one possible (up to 30mm inner diameter)

but prepare a smaller one too, in case first one doesn’t fit

Syringe to fill up the cuff
Lubricant (water soluble)

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12
Q

Equine anesthetic machine leak test pressure to hold

A

30 cmH2O

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13
Q

Pre-anesthetic patient preparation (6)

A

Fasting 12 hours prior to anesthesia
Clean the horse (a good brushing)

Take the shoes off or cover these with duct tape when going to a recovery box (risk of slipping or risk of injury due to the heel bits of the shoes)

Place an IV catheter (jugular vein - even in the field for TIVAs and not always even sutured into place if short procedure)

Administer NSAIDs and antibiotics when procedure requires (30- 60min prior to beginning)

Flush the mouth to ensure safe intubation (horses typically have food in their mouths/cheeks)

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14
Q

Preventing noise from disturbing sedated horses

A

plug the ears with cotton

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15
Q

Acepromazine use in horses

A

is a phenothiazine tranquilizer
reduces anxiety
synergic effect to other anesthetics
vasodilator - do not give to hypovolemic and hypotonic patients!
reduces the risk of shunt
anti-arrhythmic

Antiarrhythmic dose: 0,02 mg/kg IM
IV dose 0,05 mg/kg -> wait at least 15min
IM dose 0,1 mg/kg -> wait at least 30min
PO dose 0,22 mg/kg -> wait at leat 30 – 45min

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16
Q

What type of patient should you NOT give acepromazine to and why?

A

is a vasodilator - do not give to hypovolemic and hypotonic patients!
(dehydration, blood loss)

its said that it should not be used in stallions due to priapism but is okay in geldings and small doses may be used in stallions still.

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17
Q

Name 3 alfa2-agonists used in horses:

A

Detomidine 0,01 – 0,02 mg/kg IV
Xylazine 0,5 – 1 mg/kg IV
Romifidine 40 – 80 ug/kg IV

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18
Q

Describe alfa2-agonist use in horses:

A

sedation
muscle relaxation
analgesia

initial transient hypertension lasting for 5 – 10 minutes, then prolonged hypotension
may cause second degree AV-block
GIT motility depression

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19
Q

Name 2 most common opioids used in horses:

A

Morphine 0,02 – 0,2 mg/kg IV, IM
Butorphanol 0,01 – 0,05 mg/kg IV, IM, SC (faster absorption SC!)

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20
Q

Describe opioid use in horses:

A

analgesia
sedation
used together with α2-agonists (combo use decreases the doses of each required)
slows down GIT
don’t use alone in non-painful horse! may cause agitation.

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21
Q

Sedation for longer procedures…

A

consider sedative boluses (at half of orig. dose) or sedative CRI which is more stable.

e.g. detomidine and morphine CRIs

morphine never alone without alfa2-agonist going in beforehand

in the field, you don’t necessarily need a CRI pump, you can drip it in and just estimate your drips and drip time if the original volume of sedative you added to your drip bag doesn’t exceed maximum dose anyway.

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22
Q

Purpose of pain management is not analgesia alone… Also (2)

A

Reduces the amount of anesthetic drugs needed
Smoother recovery

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23
Q

principles of NSAID use

A

Inhibition of COX – 1 and/or COX – 2 enzymes:

COX – 1 -> important for regulating the perfusion of GIT mucous membranes and ensuring acid resistance

COX – 2 -> found also in kidneys, eyes, CNS; involved in the production of prostaglandins that mediate pain and support the inflammatory process

24
Q

Name 5 NSAIDs commonly used in horses:

A

Flunixin
Firocoxib (COX-2 selective, uses loading dose)

Meloxicam
Phenylbutazone
Carprofen

NSAIDs are a cornerstone of equine pain management.

25
Q

Describe paracetamol use in horses.

A

High oral bioavailability in horses: owner can administer tablets (human preparation).

Strong inhibition of central COX-3 enzyme

Inhibition of TRPV-1 receptors - important for peripheral nociception

Considered to be a weak prostaglandin inhibitor - safer for GIT

Can be combined with flunixin or replace it completely (depends on the case).

Use results in lifelong meat-for-human-consumption ban (marked into passport).

26
Q

Describe gabapentin use in horses.

A

Chronic pain (e.g. laminitis), neuropathic pain.

Low bioavailability with PO administration

There is no good clinical evidence what the correct dose to use is for pain management.

27
Q

Describe equine anesthetic induction.

A

Choose a safe and quiet surrounding (induction box at the clinic) or away from other horses in the field.

There are different ways how to support the horse during the induction, do not let the head bang against the ground.

Wall induction using a gate depicted in image. Can also use several people if no gate.

Also possible to induce without side support. Encourage the head to go down and push horse backwards at the shoulder -> almost into a sit and then down to its side.

28
Q

Muscle relaxants used in horses (2)

A

benzodiazepines
guaifenesin

Minor tranquillizers
Excellent muscle relaxation
Minimal cardiopulmonary depression
Do not give these as a single drug

29
Q

Describe ketamine use in equine.

A

Ketamine
dissociative anesthetic
produces analgesia
causes seizures and excitation when used alone
improves cardiac output

Usually combined with benzodiazepines and α2-agonists.

30
Q

Propofol is used in small animals more frequently than in horses due to large dose requirement.
What is used in horses instead?

A

ketamine

31
Q

Describe horse intubation.

A

Done blind
Head and neck stretched out straight

Insert a mouth gag
Take the tongue out of the mouth

Lubricate the ET tube
Gently enter the tube using a slight rotating movement

The tube should enter very easily - do not use any force! else something is wrong.

Use a chest compression to confirm the correct location, you can feel the air come from the tube or check ETCO2.

Fill the cuff

32
Q

Describe positioning the equine anesthetic patient

A

Dorsal or lateral recumbency.

have lots of soft padding
remove the halter
protect the eyes

have a symmetrical placement and hang the legs when in dorsal recumbency.

Stretch the lower leg forward to avoid excessive pressure on triceps muscle, radial nerve and plexus brachialis when in lateral recumbency and all legs parallel to the ground. Remember foam block between front legs.

33
Q

Maintenance drugs are usually

A

inhalational anesthetics such as sevo- and isoflurane

fast acting
quick elimination

34
Q

Describe isoflurane use in horses

A

MAC (minimum alveolar concentration) 1,2 – 1,3%
decreases respiration
dilates peripheral blood vessels
influences recovery quality in a negative way - longer procedures, hang-over effect

35
Q

PIVA

A

partial intravenous anesthesia

Inhalant anesthetics + IV anaesthetics,
reduces the side effects of different drugs.

A lot of combinations are used:
Ketamine + α2-agonist + Opioid +
Lidocaine

Or only,
Ketamine + α2-agonist
Ketamine + midazolam

Finish ket 30 min before procedure end so it has time to wear off since there is no reversal agent for it.

36
Q

What type of anesthesia is used in the field?

A

TIVA, total intravenous anesthesia

there are no vaporizers in the field

Good for procedures up to 60min, after that efficacy and safety is reduced.

Maintenance:
boluses – 30–50% of the initial dose

CRI – usually triple-drip, as will provide a more stable plane of anesthesia
(meaning alfa2-agonist + ketamine + benzo(such as mida) or guaifenesin(muscle relaxant)

37
Q

name a commonly used equine muscle relaxant that isn’t a benzodiazepine.

A

guaifenesin

comes in e.g. a 1L bag at 5%

38
Q

Anesthetic parameters you can monitor without any equipment:

A

HR; RR; MM; CRT;
pulse quality; the depth on anesthesia

39
Q

Anesthetic parameters that require special equipment to monitor:

A

ECG; ETCO2; sO2%; ETISO;
MAP; arterial PaO2 and PaCO2;
PIP (peak inspiratory pressure);
temperature and blood glucose in foals

40
Q

Assessing depth of anesthesia in horses

A

The eye:
No nystagmus and lacrimation
Eyes are moist
Light palpebral reflexes
More difficult to evaluate with ketamine on board.

Too deep –> dry eyes, no reflexes
Too light –> lacrimation, nystagmus, legs are moving

„Better light than dead“

41
Q

ETISO

A

end tidal isoflurane = the amount of anesthetic in expiratory air.

ETISO under 1,25% usually insufficient when only gas anesthesia is used. (iso MAC is approx. 1.2-1.3%)

Can be reduced by using multimodal anesthesia. Also non-painful procedures require less gas.

The end-tidal concentration of isoflurane correlates with the concentration of isoflurane in the alveoli of the lungs.

This concentration in the alveoli directly influences the MAC, as MAC is a measure of the concentration of the anesthetic in the alveoli required to produce a specific effect

42
Q

The pulse quality, does not tell you whether

A

the blood pressure is good!

pulse quality gives you an idea about the difference between systolic and diastolic pressure

43
Q

MAP (mean arterial pressure) should be at least (in horses)

A

70 mmHg (depends a bit on a muscle mass of the horse)

Under that and the capillaries of the tissues are not kept open.

Low MAP increases the risk of myopathy

44
Q

MAP (mean arterial pressure) is measured where in horses:

A

Directly from the peripheral artery (invasive technique)

or

Non-invasive with a cuff (often inaccurate with adult horses)

45
Q

Respiratory rate in anesthetized horses

A

Respiratory rate lower than in an awake horse (6-7x/min)

46
Q

Tidal volume in horses

A

Tidal volume 10-15 ml/kg like in small animals as well

47
Q

Capnography – ETCO2 in horses, should be between

A

between 35 – 55 mmHg

48
Q

Arterial gas analysis is the only way to measure

A

PaO2

Arterial PaCO2 is usually 10-15mmHg higher in blood compared to ETCO2 if there is no excessive dead space.

49
Q

When to extubate a horse

A

Extubate only after the horse swallows.

Supplement O2 – 15L/min during recovery.

50
Q

What position to recover the horse in?

A

Position,
if during the surgery on lateral -> recover on the same side (since one side of lungs is already compressed, don’t compressed the other side too).

 If during the surgery on dorsal -> recover on the left side, or the affected leg up

Prefer left side for recovery because the right lung is larger (1 more lobe than other side) = better ventilation during the recovery period.

Pull the lower front limb forward.

If extra sedation needed, 1/4th of a full dose α2-agonist.

51
Q

Methods of equine anesthetic recovery: (5)

A

free recovery
ropes at tail and head
hand assisted
sling
pool recovery

52
Q

One of the most common intraoperative complications in horses:

A

Arrhythmias:
Bradycardia
2nd degree AV-block

If HR under 20/min and starts to affect MAP, use an anticholinergic:
- butylscopolamine up to 0,3 mg/kg IV
- atropine 0.002–0.003 mg/kg IV

53
Q

Common postoperative complications in horses: (4)

A

Fractures and soft tissue injuries during the recovery

Myopathy

Neuropathy (most commonly facial nerve or
radial nerve)

Upper airway obstruction

54
Q

Bests ways to reduce post anesthetic myopathy and neuropathy

A

Myopathy risk reduction:
- high enough MAP
- correct positioning on the table and in the recovery box
- sufficient padding

Neuropathy risk reduction:
(most commonly facial nerve or
radial nerve)

  • even distribution of pressure
  • minimize the long-term stretching of the limbs
55
Q

Solution to upper airway obstruction as postoperative complication

A

10mg of phenylephrine (sympathomimetic decongestant)
diluted in 10 – 20ml 0,9%NaCl and divided between 2 nostrils

Nasal tube for the recovery or
Recovery with fixed endotracheal tube or
Tracheostomy

56
Q

Equine euthanasia protocol

A

Sedation first and foremost

Induction: ketamine and poss. a benzo if you like.
Then, pentobarbital.

Some do only sedation and pentobarbital. Sedation must be deep.

Anesthesiology (15 decks)

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