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Module 14 > Problems in Equine Anesthesia: Risks, CV, Ventilation, Recovery Techniques & Complications > Flashcards

Problems in Equine Anesthesia: Risks, CV, Ventilation, Recovery Techniques & Complications Flashcards

1
Q

what are the problems of equine anesthesia (10)

A
  1. P(A-a)O2 (VQ mismatch)
  2. hypercapnia
  3. hypotension
  4. fitness
  5. tympany
  6. temperament
  7. myelomalacia
  8. neuropraxis
  9. corneal abrasions
  10. equine post-anesthetic myopathy (EPAM, myositis)
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2
Q

what are intra operatively (anesthesized) problems

A

CV collapse

respiratory failure

metabolic disease

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3
Q

what are post-operatively (recovery) problem

A

traumatic injury

myopathy

neuropathy

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4
Q

what are post-recovery problems

A

post-anesthetic colic

laminitis

organ failure

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5
Q

what are other risk factors (7)

A
  1. ASA status
  2. duration of anesthetic
  3. pain level and therapy
  4. temperament of individual horse
  5. body size, condition and fitness
  6. breed associated problems
  7. level of monitoring and degree of intervention by an experienced anesthetist
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6
Q

how can you mitage the risks (8)

A
  1. thorough physical exam
  2. appropriate planning and preparation
  3. treatment of disease or illness if possible
  4. delay or reschedule non-urgent procedures
  5. stabilization of patient as much as possible
  6. diligent and reactive monitoring of anesthetic by experienced personnel
  7. complete procedure in as short a time possible
  8. provide best possible environment for recovery
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7
Q

what is hypotension

A

reduction in mean arterial blood pressure

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8
Q

what is the normal blood pressure in the horse

A

70-90 mmHg (concerning <60mmHg)

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9
Q

why do horses develop hypotension (3)

A

inhaled anesthetic agents decrease

  1. contractility (reduce stroke volume)
  2. heart rate
  3. systemic vascular resistance
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10
Q

what is blood pressure affected by

A

affected by cardiac output (Q) and systemic vascular resistance (SVR)

cardiac output (Q) = stroke volume x heart rate

mean arterial BP = cardiac output (Q) x SVR

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11
Q

why is hypotension significant

A
  1. reduced perfusions of organs (including muscle, lungs, liver, kidney, brain)
  2. increased risk of other complications (reduced oxygen delivery to tissue, increased lactate build up, equine post-anesthetic myopathy (EPAM))
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12
Q

how is blood pressure measured (3)

A
  1. cuff
  2. oscillometric
  3. tail or distal limb
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13
Q

what are the advantages of non-invasive blood pressure

A

quick and easy

low risk of harm

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14
Q

what are the disadvantages of non-invasive blood pressure

A
  1. less accurate
  2. not continuous
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15
Q

what are other more invasive/direct ways to measure blood pressure

A

place cannula in artery

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16
Q

what are the risks of cannula in artery (3)

A
  1. hemorrhage
  2. infection
  3. damage to periosteum
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17
Q

what are the benefits to measuring blood pressure with a cannula in the artery

A
  1. accuracy and beat to beat recording and analysis
  2. permit sampling of arterial blood for gas analysis
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18
Q

how do you treat hypotension (3)

A
  1. depth on anesthesia?
  2. hypovolemia? crystalloids, colloids, hypertonic saline (7.2%)
  3. pharmacological support
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19
Q

what are the pharmacological treatments to treat hypotension (3)

A
  1. dobutamine infusion: increases contractility
  2. ephedrine: increases contractility and SVR
  3. phenylephrine: increases SVR
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20
Q

what are the most common arrhythmia in horses

A

primary or secondary AV block

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21
Q

what are the types of AV blocks in horses (2)

A
  1. intermittent low grade high vagal tone and fitness
  2. persistent high grade, drug incuded or disease
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22
Q

what is atrial fibrillation

A

atrial flutter, atrial tachycardia

large heart, ectopic electrical focus, increased automaticity (can be drug induced)

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23
Q

what arrhythmias are abnormal in horses

A

ventricular and juncitonal

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24
Q

what is the effect tachyarrhythmias

A

reduce cardiac output

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25
Q

what are the reasons for tachycardia (4)

A
  1. hypovolemia
  2. hypoxemia
  3. pain/nociception
  4. drug induced
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26
Q

what is tachycardia race horses and ponies

A

>40 bpm race horses

>60 bpm small pony

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27
Q

what is bradycardia in race horse and ponies

A

<24bpm race horses

<30-35 bpm small pony

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28
Q

what is bradycardia a precursor to

A

asystole (not a steady decline)

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29
Q

what are potential reasons for bradycardia

A
  1. hypertension: baroreceptor repsonse
  2. hypoxemia: when myocardium becomes hypoxemic
  3. drug induced
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30
Q

what drugs are used in cardiac arrest

A

atropine and adrenaline possibly calcium in PEA

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31
Q

what are the effects of hypercapnia

A

hypoventilation

reduced exhalation of CO2

life threatening

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32
Q

what are the effects of hypoxemia

A

side effect of hypoventilation

reduced uptake of oxygen

life threatening

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33
Q

why do horses hypoventilate

A
  1. anesthetic agents
  2. positioning
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34
Q

what are the effects of inhalants on ventilation (6)

A
  1. decrease ventilatory drive
  2. desensitize medullary and carotid body chemoreceptors
  3. reduced minute ventilation
  4. respiratory acidosis
  5. increased atelectasis and V/Q mismatch
  6. hypoxemia
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35
Q

what is atelectasis

A

complete or partial collapse of the entire lung or area (lobe) of the lung

it occurs when the tiny air sacs (alveoli) within the lung become deflated or possibly filled with alveolar fluid

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36
Q

what occurs when more isoflurane is given

A

the response of the receptors decreases and the tidal volume gets lower

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37
Q

how does positioning affect ventilation

A

the weight of the abdominal contents makes it difficult to breath

38
Q

what is the normal alveolar CO2 (EtCO2)

39
Q

how does hypercapnia lead to respiratory acidosis

A

decreased alveolar elimination of Co2 causes an increase in arterial concentration (PaCO2)

leads to development of acidemia

40
Q

how can carbon dioxide be measured

A

end tidal: sampling of airway gases (PACO2)

arterial: by rapid analysis of blood (PaCO2)

41
Q

where is the most accurate blood gas analysis sample

A

fresh arterial blood samples

42
Q

what measured values can you get from blood gas analysis (6)

A
  1. pH
  2. pCO2
  3. pO2
  4. tHb
  5. Hb saturation
  6. electrolytes
43
Q

what are calculated values from blood gas analysis (5)

A
  1. base excess: relative acidity or alkalinity
  2. tCO2: total carbon dioxide combines the CO2 in all forms
  3. HCO3-
  4. anion gap
  5. hematocrit
44
Q

how do you treat hypoventilation

A
  1. depth of anesthesia
  2. provide IPPV
45
Q

what are the 5 causes of hypoxemia (5)

A
  1. inadequate inspired oxygen
  2. impaired diffusion across alveoli
  3. hypoventilation: frequent under anesthesia
  4. VQ mismatch: frequent under anesthesia
  5. shunting of blood: occurs as result of V/Q mismatching
46
Q

what is ventilation perfusion (V/Q) mismatching

47
Q

what is the compensatory response to V/Q mismatch in an unanesthetized horse

A
  1. P(A-a) O2 gradient
  2. hypoxic pulmonary vasoconstriction (HPV)
48
Q

how do high and low V/Q affect the P(A-a) gradeint

A

both increase the P(A-a) O2 gradient

49
Q

what are the effects of hypoxic pulmonary vasoconstriction (HPV) and what does inhalant anesthetics do to this response

A

compensatory vascular response that shunts blood flow away from unventilated alveoli

reduces low V/Q mismatch often due to atelectasis

compensatory response is inhibited by inhalant anesthetics

50
Q

how do you prevent V/Q mismatch

A
  1. positioning: lateral better than dorsal, still get atelectasis
  2. IPPV from beginning: prevents atelectasis
  3. air:oxygen mixture for delivery gas
51
Q

how does air:oxygen mixture for delivery gas prevent V/Q mismatch

A

FI O2 increased risk of hypoxemia, nitrogen inert gas provides a scaffold for alveoli and reduces absorption atelectasis

52
Q

what are the benefits of IPPV (4)

A
  1. may prevent decrease in tidal volume (if used from start)
  2. will help control CO2 levels (prevent hypercapnia and acidosis)
  3. use of PEEP (positive end expiratory pressure)
  4. recruitment manoeuvre
53
Q

what are the disadvantages of IPPV (4)

A
  1. gas will take path of least resistance
  2. more gas may just flow to alreadly inflated areas so increase V
  3. may impede venous return reducing Q
  4. may not improve V/Q mismatch very much
54
Q

what drugs can be used to treat V/Q mismatch

A

bronchodilators: salbutamol (inhaled), clenbuterol (IV)

and also affect CV system (vasodilation)

sweating typical

55
Q

what are the recovery risks (7)

A
  1. myopathy, neuropathy, fractures and other traumas
  2. equipment and facilities
  3. trained personnel
  4. duration of anesthetic
  5. physical state of horse
  6. age and size of horse
  7. temperament/breed
56
Q

does alleviation of pain improve recovery

57
Q

what is the effect on inhalant dependent on

A

anesthetic time

+

confounded by other drugs

58
Q

does post anesthetic sedation produce better recoveries

A

more composed recovery but longer

59
Q

does dim lighting help with recovery

A

makes no difference

60
Q

what are the techniques for recovery (9)

A
  1. free
  2. hand
  3. inflatable airbed
  4. head +/- tail ropes
  5. lift sling
  6. anderson sling
  7. hydro-pool
  8. pool and raft
  9. tilt table
61
Q

what are the requirements of recovery box (11)

A
  1. quite
  2. padded + non-slip
  3. cleanable
  4. no corners
  5. facilities for observation
  6. close to theatre
  7. oxygen
  8. scavenging
  9. escape route for staff
  10. wall rings and ceiling hooks or winch
  11. camera?
62
Q

what is assisted recovery

A

usually combined with operative sedation

topical phenylephrine or nasal tube placed

oxygen supplementation

eyes covered with soft towel/ears plugged with cotton wool

63
Q

how is a head & tail rope recovery done (5)

A
  1. continue observations: resp, musculoskeletal, eye signs
  2. two people per rope or pulley system
  3. move to sternal/stand ropes kept taught to guide and support rather than haul horse to its feet
  4. ensure airway is patent, check for residual anesthetic effects and check over for signs of injury
  5. release from ropes and allow time before moving
64
Q

what are recovery emergencies (4)

A
  1. cast/trapped limbs or head
  2. airway obstruction
  3. fractures
  4. cardiac or resp arrest
65
Q

what should be in your emergency kit (8)

A
  1. ketamine
  2. xylazine
  3. syringes
  4. needles
  5. sharp knife
  6. nasal tube
  7. ETT
  8. tracheostomy kit
66
Q

when should food be reintroduced

A

3-4 hours then reintroduce slowly

67
Q

what should you check in post recovery

A

lameness

myopathy

pain

urine and fecal output

colic check for 24 hours

68
Q

what are recovery complications (6)

A
  1. myopathy (EPAM)
  2. neuropathy (central, peripheral)
  3. trauma (orthopedic, soft tissue)
  4. airway obstruction
  5. colic
  6. catheter problems
69
Q

what is EPAM

A

equine post anesthetic myopathy

one or more muscle groups

muscles are swollen, painful, hard, hot

70
Q

what are the signs of EPAM

A

muscles are swollen, painful, hard, hot

myoglobinuria in severe cases

may affect ability to stand after anesthetic

creatinine kinase increases

71
Q

why does myopathy develop

A

failure of perfusion/oxygen delivery to muscles

72
Q

what increases the risk of myopathy (5)

A
  1. hypotension
  2. hypoxemia
  3. long anesthesia
  4. heavier horses
  5. positioning (compression of blood vessels, stretch occlusion)
73
Q

what is the treatment of EPAM (4)

A
  1. analgesia: NSAIDs or opioids
  2. fluids
  3. supportive therapies
  4. vasodilation?
74
Q

how do you prevent EPAM

A
  1. minimize duration of anesthesia
  2. position and pad well
  3. maintain oxygen delivery to muscles (BP and oxygenation)
75
Q

what are peripheral neuropathies (neuropraxis)

A

pressure or traction on nerve

can be permanent or resolve over time

76
Q

how should you position the horse

A

distribute weight evenly –> no pressure points

airbags to support muscles

padding between legs

77
Q

what is an example of a central neuropathies

A

spinal cord myelomalacia

78
Q

what is spinal cord myelomalacia

A

hind end paralysis

more common dorsal recumbency

no apparent problems during anesthesia

etiology unclear

79
Q

what are examples of musculoskeletal trauma

A
  1. skin abrasions, minor cuts
  2. orthopedic injury (fractures, disarticulations)
80
Q

what are ocular traumas

A
  1. bruising periocular area
  2. desiccation of cornea (ulceration)
81
Q

what is stridor

A

inspiratory high pitched noise

82
Q

what is stertor

A

heavy snoring sound

83
Q

what are examples of airway obstructions

A
  1. sudden or rapidly terminal complication
  2. stridor, stertor
  3. nostril flaring
  4. paradoxical ventilation
  5. absence of airflow at nostril
84
Q

what are causes of airway obstruction (4)

A
  1. nose in corner of box
  2. nasal congestion
  3. laryngeal paralysis
  4. airway swelling
85
Q

how does nasal congestion occur

A
  1. gravity
  2. longer anesthetics
  3. positioning
86
Q

how do you prevent nasal congestion (3)

A
  1. elevate head
  2. nasopharyngeal tube
  3. topical vasoconstrictor (diluted phenylephrine)
87
Q

what are laryngeal complications (3)

A
  1. trauma/swelling
  2. paralysis (pre-existing, stretching nerve)
  3. unilateral or bilateral
88
Q

how do you prevent airway obstruction (5)

A
  1. gentle intubation
  2. head position
  3. avoid overextension neck
  4. gentle extubation
  5. checking airflow immediately on extubation
  6. careful positioning of horse in recovery box
  7. dilligent monitoring of horse during recovery
89
Q

how do you deal with airway obstruction (5)

A
  1. re-anesthesia?
  2. re-intubate?
  3. tracheostomy?
  4. steroids
  5. furosemide (if pulmonary edema)
90
Q

what are factors that increase post-anesthetic colic (5)

A
  1. stress
  2. transport
  3. anesthetic/analgesia
  4. surgery
  5. feeding (or lack of)
91
Q

what are IV cannula complications (4)

A
  1. infections
  2. thrombophlebitis
  3. kink/obstruct
  4. can come off in recovery (hemorrhage if up, air embolus if down)

Module 14 (29 decks)

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