Lecture 10 Anesthesia in Horses Flashcards
1
Q
What are things you are interested when preping for horse anesthesia
A
- Presenting complaint
- Patient status
- Procedure
- IV catheter – jugular
- Wrap lower limbs
- Wash mouth
2
Q
What premedications do you use for horses
A
- Alpha-2 agonist (one of the following):
- Xylazine
- Detomidine
- Romifidine
- Opoid
- Butorphanol
3
Q
- Why would you use an alpha-2 agonist
- What are the onset of actions if given IV?
A
- Reasons:
- sedation
- anxiolysis
- adjunct analgesia
- muscle relaxation
- Onset of action 3-5 minutes (IV)
4
Q
What is the onset of action and duration of action of:
- Xylazine
- Detomidine
- Romifidine
A
- Xylazine –
- Onset of action ~3-5 minutes,
- DOA ~30-60 minutes
- Detomidine –
- Onset of action ~5 minutes,
- DOA ~60 minutes
- Romifidine –
- Onset of action ~15 minutes,
- DOA ~2 hours
5
Q
What are the cardiovascular effects of alphla-2 agonists
A
- Initial hypertension then hypotension
- Bradycardia,
- 2nd degree atrio-ventricular block
- P waves with no QRS
- ↓ cardiac output
6
Q
- What type of opioid is butorphanol
- Why use this opoid and not others
- What is another function of butorphanol other than analgesia?
A
- Mu antagonist/kappa agonist
- Other opoids are less mac sparing in horses and causes excitement
- Makes horse ‘plants’ feet
- (They don’t move their and place them down)
7
Q
What do you use for induction on horses
A
- Ketamine
- benzodiazepine
- midazolam or (this one used most commonly now)
- diazepam
- Guafenesin (GG)
8
Q
- What is guafenesin?
- What side effects does it have?
- How is it administered?
- Why administered that way?
A
- Central muscle relaxant
- Mild CV/respiratory effects
- 5% solution in 1 liter 5% dextrose
- 10% or > causes hemolysis & thrombophlebitis
9
Q
How are the induction medications given?
A
- Bolus guafenesin 25-50mg/kg (250-500ml/horse)
- Then bolus Ketamine + benzodiazepine (midazolam or diazepam) (KM or KD)
10
Q
How are horses intubated?
A
Blind intubation
- Extend head/neck in lateral recumbency
- Mouth speculum
- Tongue thru interdental space
- Over tongue, past cheek teeth, thru glottis
- Resistance?
- Pull back slightly, rotate 90° & advance
- DO NOT FORCE
- Inflate ET cuff
- Ventilatory support through Demand valve – IPPV with O2
- They become hypoxic shortly after intubation
11
Q
How are horses positioned
A
- use hoist
- position on table
- Want to have even distribution on muscles
- want to maintain blood flow
- Dont want pressure on nerves
12
Q
What are different ways to administer Intra-op Analgesia
A
- Regional anesthesia
- Can be limited by needing use of limbs for recovery
- Constant Rate infusions
- Lidocaine
- Ketamine
- Dexmedetomidine
13
Q
What Intra-op Monitoring is done in horses
A
- ECG
- SpO2
- EtCO2
- Inhalant agent monitoring –
- Inspired/Expired Isoflurane
- Invasive (direct) BP monitoring always
14
Q
What must you remember when monitoring EtCO2 in horses
A
EtCO2 is 10-15 less than PaCO2
15
Q
What is the minimum MAP you want to maintain in horses
A
70mmHg (60 in small animals)
16
Q
How do you treat hypotension in horses
A
- IV fluids
- Multi-modal analgesia/anesthesia
- To decrease amount of isoflurane used because it decreases BP
- Dobutamine CRI
17
Q
How does dobutamine work to treat hypotension?
A
- β1 > β2 - ↑ ↑ contractility & cardiac output, BP
- Horses have a lot of sererve so can do this
- Do not want peripheral vasoconstriciton so wont use norepinephrine and epinerphine to
18
Q
Why do horses get a lot of Respiratory Insufficiency during anesthesia
A
- Anatomy, size & weight => alterations in PaCO2 & PaO2
- Compression atelectasis
- Dorsal > lateral recumbency
- Anesthetics depress
- respiratory drive
- respiratory muscle function
- ventilation (rate, volume)
- response to hypercarbia/hypoxia
19
Q
What are 4 causes of hypoxemia in horses
A
- hypoventilation
- ventilation-perfusion (VA/Q)mismatching**
- right-to-left shunting of blood flow (Q)
- diffusion impairment
20
Q
Explain what happens if you have:
- V/Q = 1
- V/Q > 1
- V/Q < 1
A
- V/Q = 1 =>
- ventitlation & perfusion well matched
- V/Q > 1 =>
- lung ventilated but not well perfused (dead space ventilation)
- V/Q < 1 =>
- lung well perfused but not ventilated
21
Q
Why is EtCO2 < PaCO2 in horses
A
30-40% TV goes to large airways not Involved in gas exchange
22
Q
What happens with large colon torsions
A
- Colon twists
- Inflates with air
- Will push up on diaphragm
- Decreases TV and can increase PCO2
23
Q
What will the V/Q ratio be for this
A
- V/Q < 1
- Lung perfused but not ventilated
24
Q
When is Intermittent Positive Pressure Ventilation used in horses?
A
Always!
25
Why use Intermittent Positive Pressure Ventilation in horses?
1. Hypoventilation & ↑PaCO2
2. Consistent EtISO for stable anesthetic plane
3. Maintain adequate PaO2
* O2 supplementation + IPPV required
26
What are the 4 aspects of recovering of anesthesia in horses
1. Prevention from injury
2. Positioning
3. Airway & oxygen support
4. Sedation/analgesia
27
How are horses prevented from injury
1. padded recovery stall
2. head/tail ropes
3. head helmet
4. mats
28
How are horses positioned for recovery
* Pull lower forelimb forward
* Takes pressure off triceps muscle
29
What do you consider when giving analgesia after surgery
1. Type, length
2. Degree of pain
3. Limitations in choices/method of analgesia
* NSAIDS
* Opioids
* Limited by cost, side effects
30
What kind of sedation can you do for recovery of horses
1. Acepromazine or
2. Alpha-2 agonists
31
1. Why use acepromazine for recovery sedation
2. Negatives for using it?
1. Positives:
* Milder sedative compared to alpha-2
* Less ataxia
* Hypotension?
2. Negatives:
* No analgesia
* Slow onset of action
* IM or IV prior to disconnect from inhalant (need to plan to give before)
32
1. Why use Alpha-2 agonists for recovery sedation
2. Negatives?
1. Positives:
* More profound sedation
* Analgesia
* Faster onset
2. Negatives:
* More ataxia
* Oxygenation??
33
Why use IPPV during recovery
* Demand valve
* Allows IPPV with O2
* Rate of oxygen delivery
* Up to 200L/min
* Provides IPPV until return of spontaneous ventilation (ROSV)
* Low inspiratory flows
* Resistance to expiration
34
What rate do you put horses at during recovery to provide Oxygen insufflation
5-15 L/kg/min
35
What are causes of Airway Upper airway obstruction during recovery
1. Displacement of the soft palate
2. Nasal congestion
3. Largyngeal hemiplegia
* Upper airway surgery
* High incidence in draft breeds
36
Why do horses get Displacement of the soft palate
* Obligate nose breathers
* Extubate when swallowing
* Allows replacement of SP
* UA noise ‘snoring’
37
What happens to the nasal mucosa during anesthesia in horses?
Nasal mucosa thickens from congestion/edema during anesthesia
38
What can you do to help alleviate upper airway obstruction due to nasal congestion
1. Phenylephrine (neosynephrine) to decrease congestion
2. Provide ‘stent’ or alternate airway
* Oral tracheal tube
* Naso-tracheal tube
* Naso-pharyngeal tube
39
Why use Phenylephrine (neosynephrine) for recovery in horses
* to decrease congestion
* Significantly decreases the need for nasopharyngeal intubation
40
By providing a 'stent' or alternate airway in horses during recovery, what are some reasons why you wouldnt or would have to be careful.
* •Risk of damage to ET tube (expensive)
* •Risk of damage to laryngeal structures
* •Risk of obstruction due to kinking
* •Affect ability to stand?
41
What horses would you use stents or alternate airways
1. Large amounts of GI reflux (colic)
2. UA hemorrgage
3. +/- draft horses
42
What are the downfalls of Place naso-tracheal tube for recovery
1. Risk of damage to laryngeal structures
2. Risk of obstruction due to kinking
3. Affect ability to stand?
43
What are the downfalls of placing a naso-pharyngeal tube for recovery
1. Risk of damage/hemorrhage of ethmoids
2. Due to incorrect placement
* Middle meatus vs ventral meatus
44
What are Recovery Complications
1. Upper airway obstruction leading to pulmonary edema
2. Post-anesthetic neuropathy
* poor positioning
3. Post-anesthetic myopathy
* poor positioning
* Intra-operative hypotension
4. Fracture
