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Equine medicine > Anesthesia protocols in horses > Flashcards

Anesthesia protocols in horses Flashcards

1
Q

The risk of equine anesthesia

A

10x more risk than in other pets

5000x more risky than in humans

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2
Q

mortaility rate in horses - in different states

A

1.9%

healthy horse: 0.9%
Emergency: 7.9%

cardiac arrest is the reasion in 33%
fracture and myopathy is the cause in 32%

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3
Q

What are the risk factors

A 
age
Type of surgery
body poisition
premedication
duration of anesthesia
time of anesthesia
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4
Q

what are the risk factors - age

A

foals <2 weeks

  • unfamiliarity with an. of neonates
  • systemic illness
  • emergency

> 14 years

  • bone fracture at recoverye - long bones
  • paralytic ileus
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5
Q

risk factor - type of surgery

A

fracture repair is a risky surgery
- re-fracture at recovery
long anesthesia
shock patients

colic 12.9x more risk of mortality

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6
Q

risk factor - body position

A

lateral recumbency: 1/3 of the risk of dorsal

Lateral less risky than dorsal recumbency

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7
Q

risk factor - premedication

A

increase risk witout premedication

  • young foals!
  • stress leading to increased catecholamines

use acepromazine as premedicaiton ro reduce risk of mortaility - less susceptibility to ventricular arrhytmias

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8
Q

Risk factor - duration of anesthesia

A 
>2h = 2x more risk
>7h = 7x more risk
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9
Q

volatile anesthesia - risks

A

greater than venous

cardiovascular depression, hypotension, porr tissue perfusion –> post-anesthesia myopathy, organ failure

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10
Q

risk factor - time of anesthesia

A

out of hours - emergency surgeries at nigh will increase the risk

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11
Q

The goal - postoperative evaluation

A

main role of anesthesiologist -> to define th erisks to the owner
to select the best strategy for minimizing the risk

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12
Q

what should be provided during anesthesia?

A
  1. free airway (intubation)
  2. O2 supply
  3. IPPV (intermittent positive pressure ventilaiton)
  4. Venous access-catheter
  5. CPR = cardio-pulmonary resucitation
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13
Q

ASA classification i horses

A
  1. A healthy horse
  2. Horse with mild systemic disease (mild anemia,
    RAO)
  3. Horse with severe systemic disease (severe RAO)
  4. Horse with severe systemic disease that is a
    constant threat to life (colic)
  5. Moribund horse not expected to survive > 24 h
    (foal with uroperitoneum)
    E emergancy
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14
Q

PAtient preparation

A

history (previous anesthesia?)
physical exam (cardiovascular + respiratory system, musculoskeletal, CNS check)
Emergency cases - treat shock/stabilize (w/infusion and compensatee electrolytic imbalance)
LAboratory tests - elective sx: PCV, TPP, haematology (do not really do much more lab tests unless there is a reason for it
Fasting - 6h, water (yes) -> lung function increase, stomach rupture decreases, postop. ileus decrease
body weight

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15
Q

What should be given to the horse prior to the sedation?

A

antimicrobials
anti-inflammatories
IV catheter in jugular vein
flushing the oral cavity with tap water

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16
Q

management of sedation and general anesthesia

A
  1. premedication
  2. induction
  3. maintenance
  4. recovery
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17
Q

Which drugs are normally used for premedication?

A

Phenothiazines
Alpha2-adrenergic agents
Opioids
Benzodiazepines

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18
Q

Phenothiazines as premedication

A

acepromZINE
- decrease risk of death
improved recovery
MAC decreaase (approx 30%)

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19
Q

alpha2- adrenergic agents as premedication

A

MAC decrease
analgesia
increase urine (not good) - intraurethral catheter to collect urine

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20
Q

Opioids as premedication

A

not usually used alone, but after anesthesised
analgesic
excitement at high dses (not good)

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21
Q

Benzodiazepines as premedication

A

neonatal foals

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22
Q

use for premedication (combinations)

A

alpha2-agonists
alpha2-agonist + henothiazines/opioids
Phenothiazine + alpha2-agonist/+ opioid
benzodiazepines (neonates)

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23
Q

Drugs of induction

A

ketamine
guaiphenesin
barbiturates
propofol

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24
Q

ketamine as a drug of induction

A 
tiletamin - similar
analgesia
amnesia
MAC decrease - minimum alceolar concentration
increase cardiac output
catalepsy side effect, not good)
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25
Q

Guaiphenesin (GGE - guajoacol glycerol ether) as a drug of induction

A 
centrally acting muscle releaxant
NO sedation (not good)
No analgesia (not good)
only after sedation
NOT ALONE
severe ataxia may be followed as SE
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26
Q

Barbiturates

A 
thiopental - best choice (short acting)
fast onset
hypotension
apnoea
NO analgesia
prolonged recovery
only following sedation
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27
Q

propofol as a drug of induction

A

minimum organ toxicity
expensive
poor quality of induciton ( horse can swallow and move a bit)
minimum anagesia

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28
Q

Following premedication (drugs)

A
  1. Ketamine (2.2mg/bwkg) + Diazepam (0.1mg/bwkg)
  2. GGe: 50-100 mg/kg (ataxia) + Ketamin (2mg/kg) or + thiopental (3-5 mg/kg)
  3. Tiletamine + zolazepam (1-2mg, TelazolR. ZoletilR), popular in Zoo, ASA I-II, not narcotic drug
  4. Propofol (2mg)
  5. Inhalational anestetics (foal)
29
Q

Equipment for anesthesia

A
  • Sling door for induction
  • Mouth gag
  • Endotracheal tubes with inflatable cuff
  • Anesthesia machine: for volatile agents
  • Infusion pump/syringe pump: exact dosage for IV agent
  • Monitor
30
Q

Intubation of trachea

A
  • Flushing the mouth
  • Easy to do: poor reflex response of larynx, in lateral recumbency (ventral eye!),

Head + neck extended withdrawing slightly and rotating (lubrication) correct placement?
• Remove head collar – facial neuropathy

31
Q

maintenance of anesthesia

A

ideal anesthesia is based on

  • hypnosis
  • analgesia
  • muscle relaxation

best: different drugs used simultaneously - additive effect (can reduce: dose decreases, SE decrease)

32
Q

different types of anesthesia

A

TIVA - total intravenous anesthesia
inhalation anesthesia
PIVA - partial intravenous anesthesia - balanced

33
Q

TIVA advantage

A
  • Less depression to the cardioresp. System
  • TIVA stress < inhalation anesthesia
  • Good analgesia because of the drugs used in this technique
  • Less complication/mortality
  • Less movement during anesthesia
  • Nice recovery
  • Min. tissue toxicity
  • Less pollution to surgery room
  • Several components in combination
34
Q

TIVA Disadvantage

A

• drug accumulation, infusion pump is needed
• Methods of drug delivery:
o Intermittent injection (bolus)
o Drip technique (infusion/syringe pump) – continuous infusion

35
Q

1st group: short anesthesia (<30 mins)

A

alpha2-agonist (1/4 dose) + dissociative anesthesia (1/2 dose) -> 5-10’ (then give next bolus to maintain anesthesia)

Thiopental (1-2mg = 1/4-1/2 dose)

36
Q

2nd group: mid long anesthesia (30-60 mins)

A

hypoxia can develop
give extra O2
boluses/CRI (continous rate infusion)

37
Q

TIVA combinations

A

triple drip in CRI
GGE 5% (500ml with glucose) + 250 mg xylazine + 500mg ketamine = 2-3 ml/kg/h

ketamine (1000mg) + xylazine (500mg) + diazepam (25mg) in 1 l infusion = 2-3 ml/kg/h

38
Q

Inhalation anesthesia advantages

A
  • Depth can be changed rapidly
  • Can be monitored (FiIso, EtIso – inhaled isoflurane and exhaled isoflurane)
  • Min. drug accumulation
  • Elimination is ventilation dependent
39
Q

Inhalation anesthesia disadantages

A
  • Pollution of operation theatre
  • Cardiorespiratory depression
  • Min. analgesia
  • Expensive
  • Recovery is not as good as TIVA
40
Q

drugs for inhalation anesthesia

A

MAC- minimal alveolar concentration

  1. Isoflurane (MAC: 1.31%)
  2. Sevoflurane (MAC: 2.31%)
  3. Desflurane (MAC: 7.6%)
  4. (Halothane (MAC: 0.95% - forbidden since 2001))
41
Q

PIVA advantages

A
  • Cardiorespiratory depression decrease (MAC decr.)
  • Analgesia increase
  • Organ toxicity decrease
  • Pollution of surgical suite decrease
  • Movement in response to surgical stimuli decrease
  • Recovery increase
  • Mortality decrease
  • Muscle-relaxing effects of inhalational anesthesia
42
Q

PIVA disadvantages

A
  • Pollution

* Cardiovascular depression IV drugs accumulation

43
Q

drugs for PIVA

A
  1. Ketamine (0.5-3mg/kg/h, MAC decrease approx. 30 %)
  2. Alpha2-agonist: medetomidine (0.0035mg/kg/h, approx.. 25%)
    Romifidine (0.05 mg/kg/h)
    Xylazine (1mg/kg/h)
  3. Ketamine + alpha2-agonists (decrease approx. 50-60%- dose-dependent and additive)
  4. Lidocaine (3mg/kg/h approx. 25%) – colic patients in continuous iv drip
  5. Lidocaine (4mg/kg/h) + ketamine (3mg/kg/h) approx. 60% - colic patients
    • Decrease the doses during prolonged procedures
44
Q

IV fluid during anesthesia

A

counteract hemodynamic effects of anesthesia
replace fluid loss: 5-q0 ml/kg/h
- crystalloids (iso-, hypertonic)
- colloids (maintain vascular volume)

45
Q

thermoregulation under General anesthesisa

A 
•	Volatile anesthesia  0.4C/h decrease can occur
•	Prevent
      o	Keep warm 
      o	Avoid cold surfaces 
      o	Use re-breathing circuit
      o	Use low fresh gas flow
•	Neonatal foals: active heating, warm IV fluids, 
•	Gel cushion for foals
•	Heating lamp
•	Electric cushion
•	Hot air tube around patient
•	Normal blankets and wrappings
46
Q

stress response

A
  • Anesthesia, surgery, trauma represent a huge stress response (restore homeostasis)
  • Eq halothane anesthesia (without surgery): activate stress response
  • TIVA causes less activation
47
Q

methods modifying the surgical stress response

A
  • Balanced regimens
  • Increase tissue perfusion: avoid hypotension, hypovolemia (circulatory system)
  • Local anesthesia: prevent nociceptive signals to CNS
  • CRI butorphanol: decrease cortisol response = fewer postoperative complication + shorter recovery
48
Q

Positioning the anesthetized horse

A

• Large body mass
• 30 min in the recumbency
• General anesthesia
o Cardiovascular and pulmonary changes
o Ischemia myopathy (especially in lat recumb.)
o Unilateral forelimb-triceps myopathy (lateral recumbency)
o Bilateral hindlimb lameness (dorsal recumb.)
o Heavy horses + low ABP (arterial blood pressure)
o Neuropathy: peripheral nerves pressured or stretched (facial, femoral, radial nn.)

49
Q

padding

A

foam

water/Air cushions

50
Q

different positionings

A
  • Worst: Trendelenburg dorsal recumbency (laparoscopy)
  • Head: neutral position (overextension!)
  • Halter should be removed
  • Eyes protected
  • Limb position (like standing in normal position)
51
Q

recovery

A

negatively correlated with duration of anesthesia
improving recovery
- use of part-dose of alpha2-agonist in recovery, keep i lateral recumbency, dark, quiet box, urethral catheters
- assisted recovery (to prevent long bone fractures)
- pool/sling recovery)

52
Q

complications and emergencies

A
  1. Cardiopulmonary resuscitation
  2. Anaphylaxis
  3. Intraoperative hypotension
  4. Hypoxemia and hypoxia
  5. Hypercapnia
  6. Postoperative myopathy
  7. Postoperative neuropathy
  8. Postoperative laryngeal oedema
53
Q

Cardiopulmonary resuscitation

A

intraoperative mortality: 30% due to cardiac arrest
causes
- deep anesthesia+ hypotension
- less chance to resucitation

sign: EtCO2 decreases, weak pulse, cyanotic mucous membranes, dilated pupils, agonic breathing

treatment¨

  • discontinue an.admin
  • IPPV, chest compression 60x/min, O2 supply (ventilate with pure oxygen
  • IV drugs
54
Q

resucucation drugs

A 
epinephrine (vasoconstriction)
dobutamine (positive inotrop)
atropine (vagolytic)
calciumgluconat (heart contractive)
lidocain (ventricule tachycardia)
bicarbonate (metabolic acidosis)
55
Q

anaphylaxis

A 
uncommon <5%
vasodialtion, vessel permeability
antibiotics (penicillin, aminoglycosid)
contrast media (diatrizoate)
shortly after drug administration
- SpO2 decrease, weak pulse, ABP decrease, cardiac arrest (ECG), bronchospasm, pulmonary edema
56
Q

treatment of anaphylaxis

A 
no drugs
IPPV
ventialte with O2
fluid therapy
give: epinephrine, bronchodilator, corticosteroids, antihistamines
Check ABP, ECG
57
Q

Maintenance

A

hypoventialtion (check quality of breath)
CO decrease
V/Q mismatch ( ventilation-perfusion mismatch, hypoxemia
- gas exchange is not available in the alveoli because of e.g. fluid, shunt in lung, inflammatory are in lung -> perfusion compromised

58
Q

which agents more oftenly causes intraopertive hypotension

A

inhalation anestesia

59
Q

causes of intraoperative hypotension

A

myocardial depression (endotoxaemia), bradycardia hypotension

60
Q

Hypotension

A 
poor tissue perfusion
postop myopathy
spinal cord ischemia
cerebral necrosis
myocardial dysfunction
61
Q

treatment of hypotension

A

infusion: electrolyte/colloid/hypertonic
+ inotrop: dobutamine 1-5 microgram/kg/min infusion
ca: 10-20mg/kg (when low)

62
Q

Hypoxemia and hypoxia definitoins

signs and causes

A

Hypoxaemia: PaO2<60mmHg
hypoxia: inadequate tissue oxygenation

signs: pulsoxi-metry, blood gas

Causes

  • failure in O2 supply
  • problems with endotracheal tube, hypoventilation
  • distension of abdomnial contents - pressure on diaphragm
  • RAO, acute pulmonary edema
  • shunt
63
Q

causes of hypoxia and how to improve

A

decreased perfusion
Hb saturation decrease
decreased O2 carrying capacity (anemia)

early IPPV -tidal volume: 10-15 ml/kg

64
Q

RR

A

6-8 breaths/ min, 20 cmH20

  • increase FiO2
  • PEEP (5-10 cm H2o)
  • albuterol aerosol: bronchodilator
  • improve CO
  • pulsed delivered NO
65
Q

hypercapnia

  • cause
  • effects
  • treatment
A 
•	PaCO2>45mmHg (in artery)
•	Cause
      o	Respiratory center depression
      o	Hypoventilation
      o	Increase CO2 production: malignant hyperthermia and hyperkalemic periodic paralysis (HYPP)
•	Effects of hypercapnia 
      o	Sympathic stimulation
      o	Arrhythmia, resp. Ac
      o	Intracranial pressure increase
•	Treatment
      o	IPPV, plane an.
66
Q

Postoperative myopathy

  • cause
  • treatment
A 
Cause 
•	Large body
•	Long an.
•	Inadequate padding/positioning
•	Intraop. Hypotension, hypoxemia
Treatment 
•	Adequate padding
•	Assistance to stand
•	Mild case: light exercise, walking 
•	Mannitol inf., analgesia, E-vit, Se, DMSO, massage, inf.  renal damage (myoglobinuria)
67
Q

postoperative neuropathy

  • cause
  • treatment
  • spinal cord myelomalacia
  • cerebral cortical necrosis
A

Cause
• Inadequate padding/positioning
• Overextension of limbs (too much stress on limbs
• Radial/femoral/facial nerve injury
Treatment
• Like in myopathy - sling, splint
• Temporary conditions so should improve with treatment
Spinal cord myelomalacia
• Foal/young, hypotension, embolus
• “Dog-sit”, loss of deep pain perception
• poor prognosis
cerebral cortical necrosis
• blindness, behavioral disturbances, seizures euthanasia

68
Q

Postoperative laryngeal oedema

  • cause
  • treatment
  • complications
A

Cause

  • Bilateral nasal/laryngeal oedema
  • bilateral laryngeal neuropathy-hemiplegia
  • Negative pressure pulmonary edema

Treatment
- Temporary tracheostomy

Complications: infection, subcutan emphysema, airway obstruction, PTX

Equine medicine (17 decks)

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