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Anesthesia > Test 1- Inhalant Anesthesia > Flashcards

Test 1- Inhalant Anesthesia Flashcards

1
Q

Vapor

A

Vapor = Gaseous state of substance that is liquid at ambient temp and pressure

 Halothane, Isoflurane, Sevoflurane, Desflurane

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2
Q

Gas

A

Gas = exists in gaseous state at ambient T and P

 N2O, Xenon

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3
Q

Dalton’s law of partial pressure

A

Total pressure of a gas mixture is equal to the sum of the partial pressure of the individual gases

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4
Q

Vapor pressure

A

Vapor pressure = Pressure exerted by vapor molecules when liquid and vapor phases are in equilibrium

 Depends on temperature
 Increases with increasing temperature

 Inversely related to boiling poi

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5
Q

What’s a problem with Desflurane?

A

It’s boiling point is close to room temperature

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6
Q

saturated vapor pressure

A

Vapors have a maximum administration percentage = saturated vapor pressure

 Vapor pressure/Barometric pressure

 Ex. Iso 32%

 Vaporizers needed to reduce this to clinically useful doses

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7
Q
A
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8
Q

Solubility

A

Expressed as a partition coefficient  Concentration ratio of an anesthetic

in the solvent and gas phases

 Describes capacity of a given solvent to dissolve the anesthetic gas

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9
Q

Blood-gas partition coefficient

A

 Most clinically useful number

 Describes amount of an anesthetic in the blood vs. alveolar gas at equal partial pressure

The anesthetic in the alveolar gas represents brain concentration

 This is the location of effect

 Anesthetic dissolved in blood is pharmacologically INACTIVE

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10
Q

What is the order of gases from most soluble to least?

A

Halothane, Isoflurane, Sevoflurane, Desflurane

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11
Q

Blood-gas partition coefficient

A

Low blood-gas PC
 Less anesthetic dissolved in blood at

equal partial pressure (more in alveoli)

 Shorter time required to attain a partial pressure in the brain

 Short induction and recovery

 Ex. Iso, Sevo, Des

 Clinically more useful

High blood-gas PC

 More anesthetic dissolved in blood at

equal partial pressure (less in alveoli)

 Longer time required to attain a partial pressure in the brain

 Long induction and recovery

 Ex. Halothane

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12
Q

Uptake of inhalants

A

 Inhaled anesthetics move down pressure gradients until equilibrium achieved

 Vaporizerbreathing circuit alveoliarterial bloodbrain

 Partial pressure in the brain (Pbrain) is roughly equal to that in the alveoli (P )A

 P = gas delivery to alveoli – removal by A

blood from lungs

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13
Q

Ways to increase Pa

A
  1. INCREASE anesthetic delivery to alveoli
  2. DECREASE removal from alveoli
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14
Q

Increase alveolar delivery

A

 Increase inspired anesthetic concentration (PI)

 Increase vaporizer setting
 Increase fresh gas flow
 Decrease breathing circuit volume

 Increase alveolar ventilation  Increase minute ventilation
 Decrease dead space ventilation

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15
Q

Decrease removal from alveoli

A

 Decrease blood solubility of anesthetic

 Decrease cardiac output
 Patients with low CO will have a faster

rise of P A

 Decrease alveolar-venous anesthetic gradient

 Reflects tissue uptake of anesthetic

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16
Q

Concentration effect

A

 The higher the P , the more rapidly P

IA

approaches PI

 A high PI is required at the beginning of gas anesthesia to quickly increase P

 Offsets impact of uptake (removal of anesthetic by pulmonary circulation)

 As uptake into blood decreases, PI can be decreased

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17
Q

Anesthetic elimination

A

 Requires decrease in P A

 Same variables that affect a rise in P

 Especially agent solubility (blood- gas PC) and alveolar ventilation

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18
Q

So how would you quickly

decrease Pa ?

A

 Turn off vaporizer

 Disconnect patient and flush O2

 Turn up O2 flow
 Dilute anesthetic in circuit as it is

exhaled from patient
 Increase ventilation (IPPV)

 Increase fresh gas to alveoli

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19
Q

Minimum Alveolar Concentration (MAC)

A

 Minimum alveolar concentration of an anesthetic that prevents movement in 50% of patients exposed to a noxious stimulus

 Allows comparison of potency between agents

 Inverse relationship (high MAC = low potency)

20
Q

What’s the MAC for iso and Sevo?

A

Iso- 1.3

Sevo- 2.3

21
Q

MAC increases and decreases?

A
22
Q

Mac is…

A

MAC

 MAC is additive, therefore:
 (0.5 x MACA) + (0.5 x MACB) = 1 MACAB

 Important if:
 Changing gases in the middle of a case
 Using N2O
 Using partial intravenous anesthesia (PIVA)

23
Q

Effects of the volatile anesthetics

A

 Cardiovascular

 Respiratory
 Neurologic
 Renal

 Hepatic  Other

24
Q

CV effects of volatile anesthesics

A
25
Q

Respiratory effects of inhalant anesthetics

A

Respiratory

 Decrease ventilation
 Depress central and peripheral

chemoreceptors
 Decreased responsiveness to CO2

 Respiratory arrest at 1.5-3 MAC

 Bronchodilation

 Desflurane and isoflurane – irritating odor

 Sevoflurane – least irritating

40

https://basicsofpediatricanesthesia.files .wordpress.com/2013/07/mask- induction.jpg

26
Q

Neurologic effects of inhalanat anesthetics

A

 Increase intracranial pressure at > 1 MAC

 Increase cerebral blood flow

 Decrease cerebral metabolic rate

 Act on brain and spinal cord to produce immobility (not analgesia)

 Suppress seizure activity (except Enflurane)

27
Q

Renal effects of inhalant anesthetic

A

 Decrease glomerular filtration rate and renal blood flow due to decreased CO

 Renal failure (methoxyflurane)

28
Q

Compound A

A

 Produced from sevoflurane breakdown in CO2 absorbent (baralyme > soda lime)

 Higher concentrations formed during:  Prolonged anesthesia
 Low fresh gas flows
 Desiccated absorbent

 Nephrotoxic in rats

29
Q

Compound A

A

 Produced from sevoflurane breakdown in CO2 absorbent (baralyme > soda lime)

 Higher concentrations formed during:  Prolonged anesthesia
 Low fresh gas flows
 Desiccated absorbent

 Nephrotoxic in rats

30
Q

Hepatic effects of inhalant anesthesia

A

 Reduce liver blood flow and O2 delivery (related to decrease in CO)

 Halothane can cause hepatotoxicity (2 types)

  1. Increased liver enzymes – mild, self- limiting,
  2. “Halothane hepatitis” – immune- mediated, often fatal
31
Q

Malignant hyperthermia

A

 Myopathy occurring in genetically predisposed pigs, dogs, cats, horses, (people)

 Exposure to inhalant anesthetic
 Esp. halothane, but also iso, sevo, des

 Uncontrolled muscle contraction  severe hyperthermiadeath

 First sign is often a rapid increase in EtCO2

32
Q

Malignant hyperthermia Treatment

A

 Treatment

 Discontinue volatile anesthetic, flush with

O2, switch to new circuit if possible

 Provide 100% O2

 Administer dantrolene – muscle relaxant

 Fluids, active cooling

 Death likely despite treatment  EXTREMELY rare

 Maybe once per CAREER (>30 yrs) for an anesthesiologist

33
Q

Nitrous Oxide

A

 Used more frequently in people (lower MAC) than animals

 Max administration 75% (need > 25% O2)

 Low solubility (blood-gas PC 0.47)

 Minimal CV and resp depression

 Mild analgesic

 Transfer to closed gas spaces

 Equilibration leads to N2O accumulating rapidly (more soluble in blood) while Nitrogen leaves slowly (less soluble)

 GI tract, sinuses, middle ear, pneumothorax, GDV, cuff of ET tube

 Avoid in disease states causing increased closed gas space

34
Q

Diffusion hypoxia

A

 When N2O administration is stopped, it diffuses quickly out of the blood into alveoli (down concentration gradient)

 Displaces O2 from alveoli

 If breathing room airhypoxia

 When discontinuing N2O, provide 100% O2 for 5-10 minutes to prevent

51

35
Q

Common complications of inhalant anesthesia

A

Common complications of inhalant anesthesia

 Anesthetic-related

 Hypotension

 Hypoventilation

 Hypothermia

 Machine-related

 Closed pop-off

 Stuck inspiratory- expiratory valves

 Exhausted soda lime

 Inadequate O2 flow in non-rebreathing system

 Human error

 Intubation mishaps

 Laryngeal damage

 Stuck tube

 Aspirated tube

 Tracheal tears

 Anesthetic overdose

36
Q

Hypotension

A

Hypotension

 MAP<60 mmHg (small animal) or <70 mmHg (large animal)

 Roughly corresponds to Doppler BP of 80 or 90

 FIRST, evaluate patient and TURN DOWN THE VAPORIZER if the patient is too deep for the current level of stimulation

 This is the most appropriate and effective treatment for hypotension during inhalant anesthesia

 If patient is light, consider adding a MAC-sparing drug and THEN turn down the vaporizer

 Opioid, benzodiazepine, lidocaine, ketamine, etc.
55

 If still hypotensive, evaluate the underlying cause and treat appropriately

 Decreased vascular volume (hypovolemia)?  Give crystalloid and/or colloid bolus

 Vasodilation?
 Give vasopressor

 Decreased contractility?  Give inotrope

37
Q

Hypoventilation

A

Definition: PaCO2>40 mmHg OR EtCO2>45 mmHg

 However, EtCO2 up to 50-55 mmHg may be tolerated in certain patients (slightly complicated and controversial topic)

 FIRST, evaluate patient and TURN DOWN THE VAPORIZER if the patient is too deep for the current level of stimulation (sound familiar?)

 Perform IPPV  Manual

 Mechanical

Hypothermia

Inhalant anesthesia abolishes the normal vascular compensatory mechanisms to conserve heat

 Causes peripheral vasodilation  increased heat LOSS

Prevention is more effective than treatment

 Warm patient before induction (especially small ones)

 Bubble wrap feet

 Keep patient covered, minimize scrub time and

exposure to water/alcohol

 Increase room temp

 Forced warm air heating (BAIR hugger)

38
Q

Closed pop-off

A

What happens?

 Bag fills, breathing system pressure increases, pressure transmitted to patient lungs and thoracic cavity

 Decreased venous return (decreased preload)compressed great vessels (increased afterload)DECREASED CARDIAC OUTPUT

 Clinical signs = apnea, bradycardia, fading Doppler signalcardiopulmonary arrest

 Treatment

 Pull rebreathing bag off (usually

faster than unscrewing pop-off)

 Start CPR if patient has arrested

 Evaluate for pulmonary injury (auscultation, chest radiographs)

 Revisit habits and safety checklists

 Use quick-release or safety pop-offs

 Don’t take hand off closed pop-off

until open again (for leak check)

 Potential for pneumothorax

39
Q

Stuck inspiratory-expiratory valves

A

 What happens?

 Rebreathing system becomes bidirectional

 Causes rebreathing of expired gas  hypercarbia

 Signs?

 Easy to see on a capnograph (rebreathing waveform)

 If no capnograph, need to be more vigilant

 Should be obvious visually if valves are sticking open

 If concerned, check that valves are functional by inspiring and expiring through *flushed* system

 What are signs of hypercarbia in your patient?  Treatment

 Dry and clean valves frequently, especially after long cases

 Replace as needed

40
Q

Exhausted soda lime

A

 What happens?
 Soda lime no longer removes CO2 from

expired gases
 Patient rebreathes CO2hypercarbia

 Will look THE SAME as stuck inspiratory-expiratory valves on capnograph (rebreathing waveform)

 What else can cause this waveform?

 **Inadequate O2 flow in a non-rebreathing system**

41
Q
A

Note that the waveform does NOT return to baseline (0) between breaths

Possibilities:

Stuck insp/exp valves

Exhausted soda lime

Inadequate O2 flow in a non-rebreathing

63

system

42
Q

Intubation mishaps

 Laryngeal damage

A

 From laryngoscope or stylet most

commonly
 Be gentle! Tissues are sensitive

 Swelling can lead to post-op airway obstruction

 If you use a stylet for cat intubation, it SHOULD NOT protrude past the end of the ET tube

 Place the laryngoscope on the base of the tongue (don’t touch the epiglottis)

43
Q

Intubation mishaps

 Stuck tube

A

 Do not force an ET tube that is too big

for your patient

 It may go in, but not come out!

 What would you do?
 Re-anesthetize quickly (propofol or

alfaxalone)
 Cut tube to allow compression

44
Q

Intubation mishaps

 Aspirated tube

A

 Aspirated tube
 If patient bites through tube and aspirates the intra-

tracheal portion

 What would you do?

 Re-anesthetize quickly (propofol or alfaxalone)

 Provide O2

 Retrieve tube

 Long forceps

 Re-intubate with smaller tube, inflate cuff, then pull both tubes out together

 Tracheoscopy or bronchoscopy may be required

 Ideally, avoid this complication by providing proper

patient monitoring

 Don’t wait too long to extubate!

45
Q

Tracheal tears

A

 Not uncommon in cats

 Associated with overfilling of the

tube cuff

 Only fill until there is no leak at 15- 20 cm H2O, no more

 Do not add air unless there is a leak

 Associated with traction on tube (weight of breathing tubes) and turning/twisting patient

 ALWAYS disconnect patient from breathing system before moving

46
Q

Anesthetic overdose

A

Inhalant anesthetics have a very low therapeutic index (difference between a therapeutic and fatal dose)

Overdose can happen very quickly
 Especially at high flow rates and vaporizer settings

If in doubt about the status of your patient – turn the inhalant down or OFF while you evaluate the situation

 Remember that patient movement does not mean a conscious patient

A very low blood pressure (MAP < 50) indicates inadequate cerebral blood flow for consciousness

 (The patient doesn’t need inhalant anesthesia to stay asleep)

 TURN THE INHALANT ANESTHETIC OFF UNTIL BP HAS IMPROVED!

 Sick patients often need VERY LITTLE inhalant

 Utilize your MAC-sparing drugs – opioids, benzos, lidocaine, ketamine, etc.

 A moving patient is tolerable in most cases and preferred over a dead patient

Anesthesia (14 decks)

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