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17 – Inhalation Anesthesia Application Flashcards

1
Q

Endotracheal intubation: advantages

A
  • Airway remains protected with seal
  • Good seal=more stable anesthesia
  • Can ventilate lungs
  • Minimal workspace pollution
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2
Q

Endotracheal intubation: disadvantages

A
  • Technical failures
  • Can become obstructed if not clean or very small diameter airways
  • Laryngeal trauma
  • Mucosal irritation or pressure necrosis
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3
Q

Principals of intubation

A
  • SURGICAL plane of anesthesia removes laryngeal reflexes
  • Risk of aspiration=high
  • Intubation at light depths of anesthesia promote regurgitation
  • Always secure tube in place
  • Use gentle technique
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4
Q

Always check placement of intubation tube: use at least 3 methods

A
  • Water vapor in tube (run under cold water first)
  • Air flow: test with hair
  • Palpate neck
  • Auscultate both sides of thorax with IPPV (can be tough with larger dogs)
  • Capnogram
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5
Q

IPPV

A
  • Intermittent positive pressure ventilation
  • Ex. pushing on chest and listening for sounds on both sides
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6
Q

Cuffed endotracheal tube (ETT)

A
  • Ensures you have a good seal
  • Bevel allows it to slip between vocal cords
  • *do NOT use in birds (have complete tracheal rings, unable to expand=get more tracheal necrosis)
  • Murphy eye: safety mechanism to allow air flow still if end gets twisted or squished
  • LUBE: help create the seal (not for ease of entry)
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7
Q

Cuffed ETT and lube

A
  • Don’t use too much as it will ‘plug’ the Murphy eye
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8
Q

Tube types and apparatus

A
  • Cuffed and non-cuffed
  • Red rubber and clear tubes
  • High volume/low pressure cuff or opposite
  • Select largest diameter and correct length
  • Always check tubes are serviceable BEFORE use
  • *using scopes can be helpful
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9
Q

ETT prior to anesthesia

A
  • Chose correct DIAMETER and LENGTH
    o Palpate trachea: select range of 3 diameters
    o Pre-measure: from thoracic inlet to the incisors
    o ET tube appropriate length (to thoracic inlet/point of shoulder)
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10
Q

ETT diameter

A
  • Want it to be as close to the tracheal diameter as possible
  • If go smaller=increased resistance!
  • *size indicated=inside diameter
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11
Q

Where do you tie the kling?

A
  • Connector: secure, but problem if connector ‘falls’ off
  • Directly to tube: increase apparatus dead space
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12
Q

Problems with ETT

A
  • Kinked tubes with neck flexion
  • Damaged tubes
  • Endobronchial intubation (go to far into one lung)
  • Tracheal damage (disconnect patient from circuit when moving them to prevent)
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13
Q

What is the correct cuff inflation technique?

A
  1. Ventilate lungs (10-15cmH2O) with O2
  2. Listen for leaks around the cuff
  3. Inflate cuff until you cannot hear a leak with IPPV
  4. Turn on anesthetic vaporizer
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14
Q

Inflate and deflate cuff timing

A
  • Inflate: ASAP
  • Deflate: just prior to extubation
    o Swallow in a dog
    o Ear flick/palpebral reflex in cat
    o Brachycephalic: want for muscle reflexes (not just the swallow)
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15
Q

V-gels: Supraglottic airway device (laryngeal mask)

A
  • Designed specifically for rabbits and cats
  • Sized correctly for each animal
  • Require special lobe
  • *problems with poor fitting and potential obstruction if moving the animal
    o Should be used with a CAPNOGRAM
  • NOT a complete seal
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16
Q

Pollution in workspace

A
  • Avoid chronic exposure to trace amounts of anesthetic gases
  • Use ‘low flow’ systems (never less than 0.5 L)
  • Use proper scavenging
  • Intubate patients when possible
  • Maintain equipment
  • Check for leaks before
  • If pregnant: reduce exposures as much as possible
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17
Q

Anesthetic agent uptake review

A
  • DEPTH of anesthesia is related to partial pressure of inhalant within the brain
    o Control PP with vaporizer
    o Changes alveolar and blood PP
  • RAPID induction/recovery
    o Less lipophilic=high MAC (less potent)
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18
Q

MAC levels (lowest to highest)

A
  • Isoflurane
  • Sevoflurane
  • Desflurane
  • N2O
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19
Q

Factors affecting MAC

A
  • Sedation and powerful opioid analgesics lower amount required (especially in dogs)
  • Body temperature (hypothermia causes CNS depression)
  • Species variation
  • Age (older require less anesthetic)
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20
Q

Factors affecting anesthetic uptake

A
  • Delivered concentration
  • Blood solubility of agent
  • Lipid solubility of agent
  • Lung ventilation
  • Cardiac output
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21
Q

Delivered concentration (factors affecting anesthetic uptake)

A
  • Set vaporizer high=faster uptake
  • Promotes movement of drugs from breathing system to lungs
22
Q

Blood solubility of agent (factors affecting anesthetic uptake)

A
  • Have a larger ‘blood’ compartment
  • Slower onset: takes longer to reach equilibrium
23
Q

Lipid solubility of agent (factors affecting anesthetic uptake)

A
  • Fat soluble agents have slower uptake
  • Go to fatty tissues
24
Q

Lung ventilation (factors affecting anesthetic uptake)

A
  • More alveolar ventilation enables more drug to enter (and leave)
25
Q

Cardiac output (factors affecting anesthetic uptake)

A
  • Higher the CO=slower the uptake
    o Hard to ‘mask down’ excited patients
    o Sick animals with hypovolemia requires less anesthetic
26
Q

Where to set the vaporizer dial?

A
  • Depends on if inducing or maintaining anesthesia
  • Assess depth of anesthesia (ALWAYS check your patient)
  • Rebreathing vs. non-rebreathing systems
  • Know MAC values and what other drugs are ‘anesthetic sparing’
  • *using inhalants w/o a vaporizer is dangerous
27
Q

Assess depth of anesthesia: 3 things

A
  • Jaw tone
  • Palpebral
  • Eye position
28
Q

Rebreathing systems

A
  • Dilute fresh gas input because of LOW oxygen flows and recycled exhaled gases
29
Q

Non-rebreathing systems

A
  • ‘what you dial up, is what you get!’
30
Q

Measuring anesthetic agents

A
  • Rely on experience and vaporizer settings
  • Assess depth of anesthesia
    o Only give volatile agent that animal requires and NO more
    o Alveolar (exhaled %) most accurate measurement
  • Monitors can measure gas composition=expensive
31
Q

Isoflurane colour code

32
Q

Isoflurane MAC dog

33
Q

Isoflurane MAC cat

34
Q

Isoflurane

A
  • Rapid induction and recovery
  • Good muscle relaxation
  • Questionable analgesia
  • 0.2% metabolized in liver
  • *most commonly used inhalant
35
Q

Isoflurane cardiopulmonary effects

A
  • Dose dependent
  • MOST respiratory depressant of all IH drugs
  • Little effect on autonomic NS
  • Direct relaxation of smooth muscle of blood vessels
  • VASODILATION more pronounced compared to myocardial depression (HYPOTENSION likely to occur)
  • Little myocardial sensitization to catecholamines
  • Stable heart rate
36
Q

Isoflurane with Acepromazine

A
  • Tends to produce more HYPOTENSION
37
Q

Isoflurane clinical use

A
  • Induce with 2-4%
  • Maintain with 1-2%
    o Actually values depend on other anesthetic-sparing drugs (PIVA)
  • May need to ventilate lungs (respiratory depression)
  • Used in many species
38
Q

Sevoflurane colour code

39
Q

Sevoflurane MAC dogs

40
Q

Sevoflurane

A
  • Rapid induction and recovery
  • Not as irritation to airways/mucous membranes as in isoflurane
  • Metabolism produces few Fl- ions (not problematic)
41
Q

Sevoflurane and CO2 absorber form

A
  • Compound A and carbon monoxide=TOXIC byproducts accumulate in rebreathing systems with low O2 flow
42
Q

Sevoflurane cardiopulmonary effects

A
  • Comparable to isoflurane
  • Dose dependant
  • Vasodilation > myocardial depression (HYPOTENSION likely)
  • Hepatic blood flow preserved
  • Minimal respiratory depression (animals breath well spontaneously)
43
Q

Sevoflurane clinical use

A
  • Induce: 3-7% (usually well tolerate, sweet smell compared to isoflurane)
  • Maintain: 2-4% (depends on other anesthetic-sparing drugs (PIVA))
  • Used in many species (especially exotics)
  • Expensive (3x more than isoflurane)
  • Minimal advantages compared to isoflurane
44
Q

Sevoflurane metabolism: % and safety margin

A
  • 4-5%
  • High=rapid elimination from lungs reduce amount available for metabolism
45
Q

Sevoflurane metabolism: Fluoride ions

A
  • Can be NEPHROTOXIC in high amounts
  • Enzyme (P450) used for sevoflurane Fl- metabolism: not enough present in kidney to cause nephrotoxicity
  • NOT associated with clinical renal problems
46
Q

CO2 absorber types

A
  • CO2 absorbers contain hydroxide bases to remove CO2
  • MONO-valent hydroxides (Na, K) cause more breakdown of inhalant compared to DI-valent hydroxides (Ca2+)
  • ‘soda-lime’
  • ‘barium-hydroxide lime’
47
Q

CO2 absorbers and sevoflurane degradation

A
  • *special DI-valent CO2 absorber used with Sevoflurane
48
Q

‘soda-lime’

A
  • Has Na-OH and some K-OH
  • *monovalent
49
Q

‘barium hydroxide lime’

A
  • Has K-OH
    o Produces high operating temperatures and more sevoflurane breakdown
50
Q

Sevoflurane: CO2 absorber and fires!

A
  • Exothermic reaction
  • CO2 absorber canister temperatures normally operate 25-45 degree C)
    o High T can occur is use very low O2 flow and VERY DRY absorber
  • Sevoflurane creates the most HEAT and can cause canister FIRES!
  • Do NOT use DESSCIATED ABSORBER with sevoflurane
51
Q

Partial IV technique (PIVA)

A
  • IH drugs have little analgesia and can depress CV system (dose-dependent)
  • Other drugs can be used as an infusion or bolus to reduce IH concentration required
  • ‘anesthetic sparing’ effect
  • *useful for debilitated animals or animals undergoing invasive procedures

ANESTHESIA (27 decks)

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