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Anesthesia & Analgesia > 1: General Principles > Flashcards

1: General Principles Flashcards

1
Q

General Anesthesia

A

A state of unconsciousness produced by a process of controlled, reversible intoxication of the CNS, whereby the patient neither perceives nor recalls noxious (or other) stimuli.

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2
Q

Mechanism of action of anesthetics?

A
  • largely unknown
  • must be lipophilic to have action w/in CNS/cross BBB
  • interaction w/ inhibitory pathways:
    1. Gamma amino butyric acid (GABA) in BRAIN
    2. Glycine in SPINAL CORD
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3
Q

Triad of general anesthesia?

A
  1. unconsciousness
  2. analgesia
  3. muscle relaxation
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4
Q

How to achieve the triad of general anesthesia?

A
  • 1 drug can’t achieve all 3 unless high doses are used (resulting in undesirable side effects)
  • administer COMBO OF DRUGS that more specifically provide each component
  • allows SMALLER DOSES of each drug
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5
Q

Balanced (Multimodal) Anesthesia

A

Use of a number of different drugs to produce a state of general anesthesia, which fulfils criteria of unconsciousness, analgesia, and muscle relaxation.

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6
Q

Unconsciousness drugs?

A

Isoflurane, sevoflurane, propofol, alfaxalone, ketamine

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7
Q

Analgesia drugs?

A

Opioids, NSAIDs, local anesthetics, ketamine, alpha2 agonists

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8
Q

Muscle relaxation drugs?

A

Benzodiazepines, guaifenesin, alpha 2 agonists
- high doses of anesthetics reduce skeletal muscle tone
- use peripheral neuromuscular blocking agents if NO muscle tone is required (eye surgery)
- drugs which act on spinal cord to reduce muscle tone

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9
Q

talk about the depth of general anesthesia

A
  • higher doses of anesthetic drugs lead to deeper brain depression (but overdose causes death)
  • excess CNS depression causes suppression of reflexes associated w/ both autonomic & somatic systems
  • responsible for ID’s when just enough drug has been administered for procedure
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10
Q

Reflexes associated with autonomic nervous system?

A

hemodynamic, respiratory, thermoregulatory (BAD)

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11
Q

How to identify when enough drug has been used for a procedure?

A
  • Assess signs of CNS & ANS depression
  • depth of anesthesia is DYNAMIC depending on procedure & drugs used
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12
Q

reflexes associated with the somatic nervous system?

A

proprioceptive reflexes & muscle relaxation (GOOD)

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13
Q

Stage 1 anesthesia?

A

voluntary excitement

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14
Q

stage 2 anesthesia?

A

involuntary excitement

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15
Q

Stage 3: plane 1 anesthesia?

A

light

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16
Q

stage 3: plane 2 anesthesia?

A

surgical depth (most procedures are performed at this level)

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17
Q

stage 3: plane 3 anesthesia?

A

deep (WARNING - stage 4 is close)

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18
Q

Stage 4 anesthesia?

A

Cardiopulmonary arrest imminent

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19
Q

How to monitor the autonomic nervous system and why?

A
  • ID where anesthetic drugs influence ANS
  • ID responses made by ANS to correct abnormal states & maintain homeostasis
  • monitoring depth of anesthesia involves using ANS
  • this knowledge allows for rapid decision making
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20
Q

Depressing the sympathetic nervous system causes what?

A

Muscle relaxation

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21
Q

3 effects of general anesthesia?

A
  1. CNS depression
  2. cardiovascular system depression
  3. respiratory depression
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22
Q

What are the signs of CNS depression?

A
  • loss of consciousness
  • dampening of reflexes
  • central modulation of nociception
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23
Q

What dampening of reflexes occurs with CNS depression?

A
  1. cardiovascular -> hypotension
  2. respiratory -> hypoventilation
  3. thermoregulatory -> Hypothermia
  4. postural -> reduced muscle tone
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24
Q

What are the effects of cardiovascular system depression?

A

Overall effect is HYPOTENSION
- reflex (ex: baroreflex) suppression (centrally & peripherally)
- changes in autonomic balance
- changes in vasomotor tone (central & peripheral)
- myocardial depression
1. direct (drugs)
2. indirect (hypoxemia, hypercapnia)

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25
Q

What are the effects of respiratory depression?

A

Overall effect -> HYPOVENTILATION (hypercapnia/hypoxemia)

  • reflex suppression (decreased ventilatory response to increased partial pressure of CO2, leading to decreased pH and partial pressure of oxygen)
  • reduced muscle activity
  • alveolar collapse/small airway closure (atelectasis)
  • reduced functional residual capacity
  • ventilation/perfusion mismatch
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26
Q

What is our main objective with general anesthesia?

A

To maintain tissue perfusion, w/ delivery of oxygen & removal of waste products

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27
Q

What happens if we fail in our main objective of general anesthesia?

A

patient morbidity & mortality increase

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28
Q

there are NO SAFE ANESTHETICS, only…

A

SAFE ANESTHETISTS

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29
Q

What is the mortality in dogs that are otherwise healthy?

A

1:2000

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30
Q

What is the mortality in cats that are otherwise healthy?

A

1:2500

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31
Q

What is the mortality in horses that are otherwise healthy?

A

1:100

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32
Q

What is the mortality in rabbits that are otherwise healthy?

A

1:100

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33
Q

What is the mortality in humans that are otherwise healthy?

A

1:300,000 in hospital

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34
Q

What is anesthetic risk closely linked to and how is it graded?

A

physical status; graded 1-5

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35
Q

What improves the outcome of anesthetic risk?

A

pre-anesthetic assessment, stabilization prior to anesthesia, and anticipation of complications. Do PE, BW, & get Hx.

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36
Q

ASA 1?

A

normal healthy patient

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37
Q

ASA 2?

A

Mild systemic disease - no functional limitations

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38
Q

ASA 3?

A

Severe system disease - definite functional limitations

39
Q

ASA 4?

A

Severe systemic disease that is constant threat to life

40
Q

ASA 5?

A

moribund, not expected to survive w/o operation

41
Q

ASA E?

A

Emergency operation

42
Q

How to prevent and mitigate risks & accidents?

A
  • risk of anesthesia & surgery should always be discussed and consent obtained
  • risk increases in places w/ poor facilities/equipment, lack of training
  • vigilance is required at all stages
  • human error is common - build intervention points to prevent accidents
43
Q

Examples of vigilance to mitigate anesthetic risks and accidents?

A
  1. clearly label all syringes
  2. avoid incorrect doses, drugs, animals, & surgical procedures
  3. check, check again, & check once more
  4. never assume
44
Q

How to prevent human error?

A
  1. use SOPs & checklists
  2. avoid too many tasks at 1 time, delegate
45
Q

How to take charge in a crisis?

A
  1. clearly direct orders to person who needs to perform action
  2. use team members according to skill level
  3. give clear and precise orders
  4. don’t focus all attention on one problem
  5. gain as much information as possible & make decisions
  6. review outcome of decisions & make adjustments if necessary
46
Q

How to encourage teamwork in a crisis?

A
  1. junior people should feel comfortable enough to provide information & contribute
  2. practice role playing ex: CPR
47
Q

What are the phases of anesthesia?

A
  1. preoperative assessment
    - patient stabilization
    - provision of analgesia
  2. premedication
    - anxiolysis/sedation & initiation of analgesia if not already provided
  3. induction
  4. maintenance
    - continuation of analgesia
  5. recovery
    - aftercare
    - continuation of analgesia
48
Q

Fasting instructions for Dogs, cats, & horses?

A

fasted for at least 6-8 hrs (12 hrs is common)
- access to water until 1 hr before premed
- horses may have small amt of hay to prevent ileus during short procedures

49
Q

Fasting instructions for ruminants?

A

fasted for 24-48 hrs
- no water for last 6 hrs (gorging w/ water increases vol of rumen contents
- less than 18 hrs fasting increases risk of bloat
- very prone to regurgitation

50
Q

Why use pre-anesthetic medication?

A

calms, reduces major amount of general anesthetic (anesthetic sparing), provides analgesia, smooths general anesthetic

51
Q

pre-anesthetic medication drug choice depends on?

A
  • sp
  • facilities
  • clinician preference
  • health status of animal
52
Q

pre-med drugs include?

A
  • acepromazine
  • benzodiazepines
  • alpha 2 agonists
  • opioids
53
Q

What is anesthetic induction?

A

consciousness to unconsciousness using a major general anesthetic drug

54
Q

choice of anesthetic induction agent depends on?

A
  • sp
  • facilities
  • health status of patient
  • clinician preference
55
Q

How rapid can anesthetic induction be w/ IV drugs?

A

20-90 secs

56
Q

Why is anesthetic induction stressful for the body?

A
  • rapid changes in hemodynamics
  • need to ensure animal can tolerate changes
57
Q

what may be observed with inhalation anesthetic induction techniques?

A
  • slower
  • may observe excitement phase (stage 2)
58
Q

what is important about the maintenance of anesthesia?

A
  • long anesthetic periods require attention to life support
  • risk of complications increases w/ longer GAW
59
Q

What is the difference between deep sedation and general anesthesia?

A

If you can pass ET tube (not swallowing), it’s anesthesia (NOT sedation). Heavy sedation may still be detrimental to animal.

60
Q

What assessment of the central nervous system do you want during surgery?

A

STAGE 3 PLANE 2

61
Q

What assessment of the respiratory system do you want under GA? (RR, SATO2, ETCO2)

A

RR: 6-12 br/min
SatO2: 99-100%
ETCO2: 35-45 mmHg

62
Q

What assessment of the cardiovascular system do you want under GA?

A
  • minimum acceptable BP: 80/40 (60) mmHg (below 60 kidneys & brain are not being perfused)
  • but aim for normal of 120/80 (90) mmHg
  • good peripheral pulse quality
  • HR is not predictable of anesthetic depth!
63
Q

What other critical body systems cannot be monitored under GA?

A
  • Renal (can place urinary catheter)
  • hepatic (want to maintain good perfusion)
  • GI, musculoskeletal, etc. (keeping hemodynamics stable, leads to good perfusion)
64
Q

What can accumulate in muscles w/ long GA?

A

Lactate

65
Q

How to monitor CNS under GA?

A
  • intermittent (every 5 mins)
  • hands on approach
  • assess
    1. eye position & reflexes
    2. skeletal muscle tone (lose muscle tone as brain more depressed)
    3. breathing patterns (become more abdominal & less intercostal w/ depth)
    4. vasomotor tone (lose vascular muscle tone as brain more depressed - BP decreases)
66
Q

Eye position and reflexes with ‘light’ plane of anesthesia?

A
  • eye central
    -palpebral reflex present
  • shiny cornea
67
Q

Eye position and reflexes with ‘surgical’ plane of anesthesia (DOG/CAT)?

A
  • eye rotated ventral/medial
  • no (or slight) palpebral reflex
  • move upper eyelid to check
  • dry cornea (lube)
68
Q

Eye position and reflexes with ‘surgical’ plane of anesthesia (HORSE)?

A
  • w/ inhalation: central eye, sluggish palpebral
  • w/ injectable (ketamine based): central eye, rapid palpebral
69
Q

Eye position and reflexes with ‘light’ plane of anesthesia (HORSE)?

A

For both inhalation & injectable:
- tearing
- nystagmus (about to wake up)
- spontaneous blinking
(both eyes may not be doing the same thing)

70
Q

Pedal reflexes for testing anesthetic depth?

A
  • “all or nothing” info
  • no information on anesthetic depth
  • useful more for exotics
71
Q

Corneal reflexes for anesthetic depth?

A
  • causes blink
  • not advised (causes corneal damage)
  • loss of reflex means patient is already dead
72
Q

using anal tone to test anesthetic depth?

A
  • anus may “wink” when poked
  • useful if you don’t have access to the head to assess depth
73
Q

using muscle tone to assess anesthetic depth?

A
  • “light” -> Muscle tone +++ (rigidity)
  • ‘surgical plane’ -> ++
    -‘deep plane’ -> +
    Can assess ‘jaw tone’ in dogs & cats.
    Too much relaxation can compromise lung ventilation
74
Q

What are ‘light’ breathing patterns under GA?

A

Fast, deep, breath holding

75
Q

What are ‘surgical plane’ breathing patterns under GA?

A

rhythmic, intercostal/abdominal

76
Q

What are ‘surgical plane’ breathing patterns under GA in Ru?

A

Ru may have fast & shallow (tachypnea) breathing pattern

77
Q

What counts as life support that should be used under GA?

A
  • warmth
  • hydration
  • BP support - IV fluids, drugs
  • delivery of O2 & lung ventilation
  • protect musculoskeletal/NS
    1. esp heavy & lrg animals
    2. positioning & padding
78
Q

How is body heat lost during surgery?

A
  • convection
  • radiation
  • conduction
  • evaporation
79
Q

What factors other than heat loss cause body temperature to drop during GA?

A
  • lack of muscle activity
  • depressed metabolic rate
  • vasodilatory drugs
  • re-setting of thermoregulatory center by some drugs
80
Q

Heart can fibrillate at what temperature?

A

28 C

81
Q

Arrhythmias can occur at what temperature?

A

32 C

82
Q

When should you supply warmth to the patient?

A

throughout all phases of anesthesia (starting after pre-med

83
Q

What causes fluid loss under GA?

A
  • cold, dry gases (non-rebreathing circuits) - evaporative
  • open body cavities
  • bleeding
  • maintenance (cant drink under anesthesia)
84
Q

How to administer fluid support during GA?

A
  • balance electrolyte solutions
  • colloid oncotic agents
  • monitoring ‘ins/outs’ where possible
    1. assess blood loss (1 gram = 1 mL)
    2. normal urine production
    3. evaluate suction jar
85
Q

What is normal urine production?

A

1-2 ml/kg/hr

86
Q

What to do during recovery period after GA?

A
  • continue monitoring & life support
  • continue analgesia
  • sedation may be required
  • special techniques w/ lrg animals
87
Q

Where should a patient go for the recovery period?

A

Depends on case & patient condition:
- day patient can go home once fully recovered
- short period in recovery area
- ICU where life support continues

88
Q

Why is analgesia important?

A

if patient is comfortable, GA will go more smoothly

89
Q

Why use pre-emptive analgesia?

A
  • anticipate painful event
  • stop/blunt pain pathway from firing
  • minimize potential for wind up pain/sensitization
90
Q

Why use multi-modal analgesia?

A
  • different drugs combat pain in different ways
  • type of pain may determine which analgesic you try 1st
91
Q

What can happen if pain goes untreated?

A

Acute pain can become chronic pain

92
Q

what is acute pain?

A

symptom of disease itself (protective)

93
Q

what is chronic pain?

A

is DISEASE itself

Anesthesia & Analgesia (2 decks)

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