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
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
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
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
5
Q
IPPV
A
- Intermittent positive pressure ventilation
- Ex. pushing on chest and listening for sounds on both sides
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)
7
Q
Cuffed ETT and lube
A
- Don’t use too much as it will ‘plug’ the Murphy eye
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
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)
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
11
Q
Where do you tie the kling?
A
- Connector: secure, but problem if connector ‘falls’ off
- Directly to tube: increase apparatus dead space
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)
13
Q
What is the correct cuff inflation technique?
A
- Ventilate lungs (10-15cmH2O) with O2
- Listen for leaks around the cuff
- Inflate cuff until you cannot hear a leak with IPPV
- Turn on anesthetic vaporizer
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)
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
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
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)
18
Q
MAC levels (lowest to highest)
A
- Isoflurane
- Sevoflurane
- Desflurane
- N2O
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)
20
Q
Factors affecting anesthetic uptake
A
- Delivered concentration
- Blood solubility of agent
- Lipid solubility of agent
- Lung ventilation
- Cardiac output
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
Cardiac output (factors affecting anesthetic uptake)
- Higher the CO=slower the uptake
o Hard to ‘mask down’ excited patients
o Sick animals with hypovolemia requires less anesthetic
26
Where to set the vaporizer dial?
- 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
Assess depth of anesthesia: 3 things
- Jaw tone
- Palpebral
- Eye position
28
Rebreathing systems
- Dilute fresh gas input because of LOW oxygen flows and recycled exhaled gases
29
Non-rebreathing systems
- ‘what you dial up, is what you get!’
30
Measuring anesthetic agents
- 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
Isoflurane colour code
- Purple
32
Isoflurane MAC dog
- 1.28
33
Isoflurane MAC cat
- 1.71
34
Isoflurane
- Rapid induction and recovery
- Good muscle relaxation
- Questionable analgesia
- 0.2% metabolized in liver
- *most commonly used inhalant
35
Isoflurane cardiopulmonary effects
- 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
Isoflurane with Acepromazine
- Tends to produce more HYPOTENSION
37
Isoflurane clinical use
- 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
Sevoflurane colour code
- Yellow
39
Sevoflurane MAC dogs
- 2.4%
40
Sevoflurane
- Rapid induction and recovery
- Not as irritation to airways/mucous membranes as in isoflurane
- Metabolism produces few Fl- ions (not problematic)
41
Sevoflurane and CO2 absorber form
- Compound A and carbon monoxide=TOXIC byproducts accumulate in rebreathing systems with low O2 flow
42
Sevoflurane cardiopulmonary effects
- Comparable to isoflurane
- Dose dependant
- Vasodilation > myocardial depression (HYPOTENSION likely)
- Hepatic blood flow preserved
- Minimal respiratory depression (animals breath well spontaneously)
43
Sevoflurane clinical use
- 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
Sevoflurane metabolism: % and safety margin
- 4-5%
- High=rapid elimination from lungs reduce amount available for metabolism
45
Sevoflurane metabolism: Fluoride ions
- 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
CO2 absorber types
- 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
CO2 absorbers and sevoflurane degradation
- *special DI-valent CO2 absorber used with Sevoflurane
48
‘soda-lime’
- Has Na-OH and some K-OH
- *monovalent
49
‘barium hydroxide lime’
- Has K-OH
o Produces high operating temperatures and more sevoflurane breakdown
50
Sevoflurane: CO2 absorber and fires!
- 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
Partial IV technique (PIVA)
- 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
