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Equine anaesthesia, sedation Flashcards

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1
Q

What to give for a Premed in horses? What if a colic?

A

ACP (40 mins before start prepping horse)
- still use in breeding stallions, just warn owner of risk
- don’t use in colics as causes hypotension and likely already hypovolaemic (and lasts long time and not reversible)
Romifidine when prepping (e.g in stocks)
IM detomidine at same time as ACP if very difficult horse
(A2s not ideal for colics as reduce CO by 40-50% but still use as need good sedation - use xylazine as shorter acting so shortest negative CV effects)
NSAIDs or opioids

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2
Q

Which a2 agonist is licensed for IM injection?

A

Detomidine only

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3
Q

What to pre-med and induce a foal with if suspected porto-systemic shunt?

A

Just morphine pre-med
Induce with alfaxalone

Can’t use ACP as affects blood flow to liver
Benzodiazpeines contraindicated as gut already makes benzodiazepines which are not being broken down by liver so would have too much going to brain -> seizures

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4
Q

Induction: Licensing? Onset of action?

A

Ketamine and thiopental licensed in horses
Usually ketamine + benzodiazepine (midazolam licenced)
Ketamine takes 90s-2m to cause recumbency
Thiopental takes 20s for recumbency (more ataxia?)

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5
Q

Maintenance agents used in horses: Options? Side effects?

A 
Isoflurane
Sevoflurane
- not licensed in horses (only dogs, cats and rabbits)
- but poss better recovery
- more expensive?
Both cause vasodilation so HR goes up
Ketamine bolus if light
Thiopental bolus if waking up
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6
Q

What are the minimum alveolar concentrations (MAC)s of isoflurane and sevoflurane?

A

Isoflurane: 1.3
Sevoflurane: 2.3
But monitor individual horse to see if needs more or less than this

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7
Q

How much oxygen to give a horse during anaesthesia?

A

4-10ml/kg
A bit is used by capnography (accounted for if use 10ml/kg)
E.g. give 700kg horse 7L oxygen

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8
Q

Opioids in horses: Which ones are licensed? Pros and cons?

A 
Licensed: 
- pethidine
- butorphanol
- buprenorphine
Butorphanol:
- poor analgesia
- excitable effect when given with sedation (so just don't use)
- good for antitussive for BAL
- don't use when doing NG tube as don't cough when going into trachea
Buprenorphine:
- only partial mu agonist
Fentanyl:
- full mu agonist
- licensed in other species
- but need infusion as very short acting (very lipophilic)
Methadone:
- full mu agonist
- licensed in other species
- but can cause profound facial twitching in horses (can still use but avoid for head surgery etc)
Morphine:
- full mu agonist 
- not licensed in any species but used under cascade
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9
Q

A2 agonists in horses: Pros and cons?

A

Xylazine:
- good for standing sedation continuous infusion as shortest onset and action so will respond quicker to changes of rate and will recover quicker when infusion stopped
Detomidine:
- only one that is licensed IM
Romifidine:
- less ataxia than detomidine
All cause diuresis due to ADH inhibition and action of DCTs and collecting duct
All cause hyperglycaemia
Initial vasoconstriction and bradycardia - reduced CO but MAP about normal

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10
Q

How does the analgesic effect of A2 agonists compare to their sedative effect?

A

Analgesic effect lasts 1/2 - 1/3 time of sedative effect

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11
Q

NSAIDs in horses: Licensing? Pros and cons?

A 
Licensed:
- phenylbutazone
- suxibutazome
- flunixin
- ketoprofen
- carprofen
- aspirin
- meloxicam
- firocoxib
...... others
Meloxicam:
- most palatable
- 72h FEI withdrawal (others are 8 days)
- good in shetlands as syringed amounts more practical than bute sachets
Bute and flunixin same efficacy but flunixin more potent
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12
Q

Epidurals in horses: Which type? What drugs used?

A

Lumbosacral very painful so generally just do sacrococcygeal
Don’t use local (except for caudal epidural for tail/perineum) as risk going off back legs
Can put a2 agonists in but..
So just opioids
Usually combo of methadone and morphine as different lipid solubilities:
- methadone has quicker effect but only lasts 4 hours
- morphine takes longer to work but lasts for 24h

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13
Q

What is phenylephrine used for in horses? What is it?

A

= A1 agonist
During GA to cause vasoconstriction to increase BP (lots - aim for MAP 160-180) e.g. to make spleen smaller for nephrosplenic entrapment colic surgery

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14
Q

What can be used for euthanasia on the surgical table, other than somulose? Why?

A

KCl (dilute salts in tap water)
Cheaper than somulose
Do get lots of agonal breathing

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15
Q

What is atracurium?

A

Neuromuscular blocker

May be given when on ventilator

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16
Q

What can be done to help improve ventilation and perfusion under GA?

A

All dorsal recumbencies put on a ventilator as poor lung perfusion
Salbutamol (B2 agonist) inhaler (2 puffs per 100kg) - causes vasodilation and bronchodilator to open alveoli
Recruitment manoeuvre = artificially large break to inflate lungs (inspiratory pressure of 40-45 2-3 times)

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17
Q

What is important to know about soda lime colour?

A 
Changes colour during use but will change back so not reliable assessment at beginning of a surgery
Use FI (inspired concentration)
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18
Q

How to assess anaesthetic depth in horses?

A

HR and RR often don’t change with depth or pain so don’t rely on these

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19
Q

What should BP be under anaesthesia?

A

SBP >80
MAP >60/70 (>70 if higher risk of myopathy e.g. big horse)
DBP >40

If HR low (e.g. 20) but BP high then don’t worry too much

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20
Q

What can be used if BP falling under GA?

A

Dobutamine - increases heart contractility (and HR)

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21
Q

What is dampening of BP monitoring?

A

Underestimation of systolic pressure
Flush arterial line with heparin saline as can be caused by blood clots
So if low BP, check trace before giving dobutamine etc

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22
Q

What causes the anacrotic notch on a BP trace?

A

Recoil of aorta

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23
Q

Which arteries are used for invasive BP monitoring in horses under GA?

A

Facial (just briefly wipe and spirit as can cause spasm if scrubbed)
Transverse facial
Metatarsal (sterile prep as infection would be v bad)

Don’t move art lines as interferes with trace

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24
Q

Complications of arterial catheters?

A

Trauma
Haematoma
Emboli
Infection

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25
How does the level of the transducer for BP monitoring under anaesthesia affect the trace?
Must be at level of heart If above, will falsely reduce BP If below, will falsely increase BP
26
Why do we want the MAP >60 under GA?
If MAP <60, blood stops faint to skin, muscles etc | Horses often get myopathy - can panic from this and get fracture etc
27
What is distal pulse amplification?
Further away the arterial catheter is from the heart, there is a false increase in SBP and false decrease in DBP but proportional so MAP stays about the same
28
Why may horses have a bifid P wave?
Large atria so not quite synchronised atrial contraction as takes longer to depolarise (Biphasic different thing and not normal, goes above and below axis)
29
Which lead is used for equine ECGs? Where are the leads placed?
Lead I (base-apex) +ve lead: yellow, heart apex -ve lead: red, right jugular furrow Grounding lead: green, anywhere
30
Pulse oximetry: What does it measure? How does it work?
Percentage of peripheral Hb saturated with oxygen (SpO2) = indirect measure of arterial oxygen saturation (SaO2) Optical device that measures the difference in absorption of infrared and red light between oxygenated Hb (HbO2) and non-oxygenated Hb (Hb) by emitting red and infrared light to a photodetector HbO2 absorbs more infrared light Hb absorbs more red light Clip placed on non pigmented area: tongue, axilla, inguinal folds, prepuce, vulva
31
What is pulse oximetry affected by?
``` Light Movement Pigmentation Poor peripheral perfusion - relies on tissue perfusion so won't work if: - hypovolaemia - low BP - hypothermia - vasoconstriction e.g. from a2 agonists ```
32
Why is pulse oximetry not very sensitive for PaO2 when on oxygen therapy?
If on 100% oxygen, 5 times the amount of oxygen of normal 21% air PaO2 should be 100mmHg with normal 21% oxygen from air So PaO2 is 5 times greater the inspired oxygen fraction (FiO2) So if on 100% oxygen, PaO2 should be 500mmHg PaO2 of 100mmHg = 100% SpO2 So SpO2 will not detect changes in PaO2 past 100mmHg Therefore, important to do blood gas analysis when on oxygen therapy (could drop quickly from 500mmHg to 100mmHg but pulse oximeter will still have SpO2 of 100%)
33
What is the cut off for hypoxaemia with pulse oximetry?
95% SpO2 = 80mmHg (normal) | 90% SpO2 = 60mmHg (severe hypoxaemia)
34
Advantages and disadvantages of pulse oximetry?
Advs: - non invasive - continuous (arterial blood gas more precise but not continuous and invasive) Disadvs: - if anaemic, SpO2 can be falsely reassuring as Hb still saturated to normal levels - doesn't detect difference between Hb, carboxyHb, metHb, sulfHb, carboxysulfHb which are non functional = falsely high readings (can use co-oximeter to measure these) - doesn't detect hypoventilation or apnoea (takes several mins for apnoea to result in hypoxaemia detected by pulse oximetry)
35
What abnormal capnograph traces are there under GA? Appearance? Cause? What to do about them?
Hypoventilation: - plateau goes above 45 - check O2 high enough - can increase RR - but often leave unless >60 as hypercapnia helps stimulate cardiac function Hyperventilation: - plateau goes below 35 - check PCO2 on blood gas analysis and if also low then reduce TV or RR if on ventilator Rebreathing: - baseline above 0 - if on Mapleson D, fresh gas not high enough - faulty one way valves e.g. rusted, soda lime ran out on circle Prolonged expiration - shark fin - bronchoconstriction due to anaphylaxis just given, asthma, tube blockage Cardiogenic oscillations: - oscillations on inspiratory downstroke - listen for eCG beep to check is this - nothing to worry about Leaky cuff: - dodgy wobbly trace Fighting ventilator: - smaller breaths in between ventilator breaths - if had neuromuscular blocker, may be wearing off Dying: - dropping off to very low trace - earliest indicator of crashing One lung ventilation: - trace half of expected e.g. ETCO2 of 22 - e.g. if doing lobectomy so only ventilating one lung - cats: long ETT and accidentally went down one bronchus
36
Cause of different ETCO2 and PCO2 values?
Ventilation-perfusion mismatch (alveoli or vessels squashed)
37
Where to put hoists on horse legs when lifting under GA?
Below fetlocks Usually don't put above fetlocks as risk of splint bone button fractures But have to in very large horses if ceiling not high enough
38
How long can you give 100% oxygen to a horse under GA?
No more than 8h as toxic
39
What is the Ritchie whistle?
High pitched whistle when taking off CO2 Tells you that O2 supply is unplugged Valve in circuit that will switch to room air
40
Why are pregnant/lactating mares at a higher risk of fracture during GA recovery?
Less Ca in bones from milk production
41
Which recumbency has a higher risk of myopathy under GA? Why?
Lateral e.g. triceps myopathy
42
When would you use total intravenous anaesthesia (TIVA) rather than inhalational?
Field anaesthesia | Surgeries <1hr
43
What does a wound catheter do?
Inject bupivacaine periodically | Reduces risk of complications
44
What are the phenomenons for why it hurts around a wound?
Hyperalgesia | Allodynia
45
Define efficacy, potency, affinity and avidity?
Efficacy (Emax) = the maximum effect which can be expected from the drug, regardless of dose (ie increasing the dose will not increase the effect) Potency = the amount of drug needed to produce a given effect (e.g. EC50 = concentration or dose of drug needed to cause 50% of the drug's maximal effect) - a drug with a lower potency may have to same effect as another drug but at higher concentrations Affinity = how strongly a drug binds to receptors Avidity = the cumulative binding strength of multiple binding sites
46
Why can sedation result in nasal oedema? Why problem?
Due to head being lower down | Problem for GA recovery when remove ETT
47
How to change a % solution into mg/ml?
Just x10!! E.g. 10% solution = 100mg/ml (% of 1g, 1g=1000mg, % of 1000mg = mg/ml)
48
Converting ug to mg?
ug/1000 = mg
49
How to calculate how much of an original concentration solution to use to create a new concentration?
(New concentration x volume wanted)/Original concentration Minus what you need to add from the volume wanted
50
How quick do you need to drips/s for a 500ml fluid bag to be used over 1 hour?
2.7drips/s
51
Jugular catheters: Which way do short and long stays go? Why? Method?
Long stay: down jugular (so don't use during surgery as if gets knocked then risk air embolism - use if dangerous horse though as won't be able to change to long stay after recovery) Short stay: up the vein (so if get knocked, just leak blood, rather than air embolus risk) Can use US and blood gas analysis to check in jugular not carotid (and blood dark red) Non sterile scrub, 2ml mepivacaine, sterile scrub, sterile gloves, catheter in, 3x sutures, flush
52
Fluids for haemorrhage due to guttural pouch mycosis with PCV 18% and TP 58 (epistaxis 4 days ago and again today), BAR?
Bright in self and chronic blood loss so compensating Wait to give transfusion until after surgery as risk dislodging clot and causing catastrophic fatal bleeding Once internal carotid ligated give blood transfusion (needed for good oxygen carrying capacity for recovery from GA as need energy to get up - induction less of a worry)
53
How to test the compatibility of a blood transfusion?
Can mix donor and recipient blood and look for haemagglutination and hamolysis under microscope
54
How much blood can you take from a donor horse for blood transfusion?
<20% (15-18ml/kg) of blood volume (take as quickly as possible) Generally should only take 5L from 500kg horse
55
Suitable donor for blood transfusion?
``` Free from infectious disease (EVA, EIA) - can test (takes about a week) No previous transfusion Not had foal Up to date with vaccinations Dental prophylaxis Adult Well behaved Quarter horses good as more likely a good blood type Ie preferably healthy >500kg gelding ```
56
What to do if anaphylaxis to blood transfusion? Signs?
``` Stop, adrenaline, steroids Signs: - increased RR - increased HR - hives - sweating ```
57
How much blood to give for transfusion?
25-50% of volume lost (rest made up by fluids given to increase intravascular volume)
58
Adverse effects of blood transfusions in horses?
Haemolysis Fever Infection Anaphylaxis
59
When are changes in TP and PCV seen after acute blood loss?
After 8h | No change initially even straight after 40% loss
60
What are good indicators of acute haemorrhagic shock?
Kidney markers | Lactate (tells you if coping with lack of blood) - worry if increased
61
Can you give hartmann's through same IV line as blood?
No Ca in Hartmann's causes clotting Flush in between
62
Blood transfusion equation for amount to transfuse?
ml = BW x 80ml/kg x ((desired PCV-actual PCV)/donor PCV)
63
How to estimate the amount of blood a haemorrhaging horse has lost?
If HR, RR, CRT normal: <15% If HR or RR or CRT increased: >15% If BP normal: <30% If BP decreased: >30% If anxious or depressed and cool extremities: >30% >40% if severely increased HR, increased RR, very pale mucous membranes, severe hypotension and obtunded, cool extremities
64
How much fluids to give for volume resuscitation e.g. when hypovolaemic?
4ml/kg (2L) hypertonic saline over 15 mins (increases circulating volume for 20-30 mins) Then follow every 1L of hypertonic with 10L isotonic fluids
65
How much fluids to give for volume resuscitation e.g. when hypovolaemic?
4ml/kg (2L) hypertonic saline over 15 mins (max can give in 24h) (increases circulating volume for 20-30 mins) Then give 10ml/kg at a time of isotonic fluids, then re-assess (monitor HR, BP, mm)
66
Which isotonic crystalloids to use in suspected large colon torsion colic case?
Hartmann's as likely metabolic acidosis Blood Na and Cl will go up if given hypertonic saline (need to check K levels) Can spike with Mg or K once taken blood samples Recheck electrolytes after giving spiked fluids
67
Why does ketamine have a negative inotropy effect in sick animals?
Ketamine is a myocardial depressant But in normal animals, don't see effects because also sympathomimesis In sick animals, sympathetic system maxed out so get negative isotropy effect
68
Why can't you give diazepam alone to a horse? Exception?
Causes excitement and panic due to ataxia from decreased muscle tone Exception = seizing (centrally acting anti-seizure drug)
69
Pre-med and induction of colic case?
Pre-med: xylazine | Induction: ketamine and diazepam
70
Why are sick colic cases hypovolaemic?
Gram negative bacterial LPS cause endotoxaemia which causes massive peripheral vasodilation (which is why mucous membranes are congested, not pale)
71
Why do endotoxic horses get brick red mucous membranes?
= congested Peripheral vasodilation Very quick CRT because blood has pooled in capillaries
72
What does it suggest if a horse has diarrhoea and is dehydrated and hypovolaemic post colic surgery?
Colitis - sloughing of wall after surgery Fluid loss due to excessive secretion due to inflamed colon walls Lost fluid, electrolytes, protein
73
Fluids to give a horse which is dehydrated and hypovolaemic post colic surgery with diarrhoea (PLE)? Other drugs?
Low oncotic pressure so colloids best (4-5ml/kg, can use up to 20ml/kg) Colloids can last 24h Then hartmann's Check electrolytes - spike Hartmann's with K or Mg if needed Lidocaine poss pro-kinetic but poor evidence Polymixin B (only evidence of being anti-endotoxic if given before happens, v expensive) If just gave hypertonic saline/crystalloids -> fluid would just move out into ISF/ICF as low oncotic pressure -> oedema (uncomfortable and harder for blood to perfuse tissue) Ideally would use albumin but v expensive so just used for humans Plasma better than colloids as contain globulins but difficult storage and would need 1L of plasma to raise TP by 1g
74
Why is isotonic saline not used IV anymore?
Causes metabolica acidosis
75
Problems with Hartmann's?
Causes hypernatraemia with long term use which increases mortality
76
Why can't give pure water IV?
Causes haemolysis
77
What happens to the pH, HCO3-, H2CO3 and CO2 with respiratory acidosis, respiratory alkalosis, metabolic acidosis and metabolic alkalosis? Why? How to work it out?
Respiratory acidosis: - pH decreases - others all increase (CO2 cause, HCO3- compensatory) - kidneys compensate by increasing HCO3- Respiratory alkalosis: - pH increases - others all decrease (CO2 cause, HCO3- compensatory) - kidneys compensate by decreasing HCO3- Metabolic acidosis: - all decrease (HCO3- cause, CO2 compensatory) - lungs compensate by hyperventilation to decrease CO2 Metabolic alkalosis: - all increase (HCO3- cause, CO2 compensatory) - lungs compensate by hypoventilation to increase CO2 (but limit due to respiratory drive) Every time there is increased pCO2 in arterial blood = respiratory acidosis Every time there is decreased pCO2 in arterial blood = respiratory alkalosis Then must have opposite for metabolic?
78
Causes of respiratory acidosis, respiratory alkalosis, metabolic acidosis and metabolic alkalosis?
``` Respiratory acidosis: - hypoventilation - anaesthesia/drugs - diseased lung Respiratory alkalosis: - hyperventilation - altitude Metabolic acidosis: - renal disease - intestinal (D+/V+) - hyperCl, hyperK - addisons - CA inhibitors - ketones - anaerobic metabolism - endotoxaemia - sepsis Metabolic alkalosis: - gastric V+ - hypoCl, hypoK - diuretics - excess HCO3- administration - hyperaldosteronism ```
79
What is base excess? Significance?
= measure of all bases in blood, not just HCO3- A large positive means can cope with added acid Negative means needs alkali as not coping with more acid
80
What to use to sedate: - a flighty rearing colt to examine a wound? - a box shy, needle shy horse for 2hr transport - a head shy horse for reliable sedation for equine dentist without vet having to attend? - intermittently thrashing horse being rescued with one chance for reliable sedation?
Flighty colt: IM ACP, detomidine and butorphanol Box shy horse for transport: ACP gel Sedation for dentist: detomidine transmucosal gel Thrashing horse being rescued: IM ACP, detomodine and butorphanol

Equine (14 decks)

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