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N926 Pharmacology > Inhalational Agents II > Flashcards

Inhalational Agents II Flashcards

1
Q

Ether Day

A

October 16, 1846

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2
Q

Who successfully demonstrated how to use ether?

A

William T.G. Morton

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3
Q

Sevoflurane BP

A

57°

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4
Q

Sevo VP

A

159mmHg

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5
Q

Sevo Blood:Gas

A

0.65

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6
Q

Sevo Oil:Gas

A

47

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7
Q

Sevo MAC

A

2%

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8
Q

Isoflurane BP

A

49°

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9
Q

Iso VP

A

238mmHg

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10
Q

Iso Blood:Gas

A

1.46

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11
Q

Iso Oil:Gas

A

91

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12
Q

Iso MAC

A

1.2%

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13
Q

Desflurane BP

A

24°

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14
Q

Des VP

A

669mmHg

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15
Q

Des Blood:Gas

A

0.42

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16
Q

Des Oil:Gas

A

19

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17
Q

Des MAC

A

6%

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18
Q

Nitrous Oxide BP

A

-88°

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19
Q

N2O VP

A

38,770mmHg

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20
Q

N2O Blood:Gas

A

0.42

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21
Q

N2O Oil:Gas

A

1.4

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22
Q

N2O MAC

A

104%

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23
Q

What factors influence PK?

A

Absorption - uptake
Distribution - biotransformation
Excretion - elimination

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24
Q

Factors affecting FI

A

Fresh gas flow
Breathing system volume
Machine absorption

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25
Q

Factors affecting FA

A

Alveolar concentration

Agent blood solubility
Alveolar blood flow
Partial pressure b/w alveoli & venous blood

FA > ET

  • Venous admixture
  • Alveolar dead space
  • Non-uniform distribution
26
Q

Inhalational Agents MOA

A 
???
NMDA receptors
Tandem pore K+ channels
VGNa+
Glycine receptors
GABA
Huff enough gas ya pass out
27
Q

CNS Sites

A

Altered transmission in the cerebral cortex

Brain stem arousal centers - amnesia
Central thalamus (pain relay center) - analgesia
Spinal cord (skeletal muscle relaxation) - areflexia
28
Q

Meyer Overton Theory

A

Lipophilicity = potency
Accepted dogma
BUT exceptions exist

29
Q

CNS Effects

A 
↓ CMRO2
↑ CBF (dose dependent)
Cerebral vascular responsiveness to CO2
- Vasodilate or constrict
ICP concern → mild hyperventilation ↓ CO2 to compensate (vasoconstriction to prevent ↑ ICP)

EEG burst suppression
Evoked potentials ↓ amplitude ↑ latency
Spinal surgery w/ nerve monitoring consider TIVA

30
Q

Uncoupling

A 
Combined effects
Increased w/ Sevoflurane
↓ CMRO2 ↑ CBF 
Exception: Nitrous oxide
Mild hyperventilation helps attenuate ↑ CBF
Cerebral vasculature responsive to CO2
31
Q

Developmental Neurotoxicity

A 
No evidence to support in human studies
PANDA study, GAS trial, & population-based cohort study
↓ anesthetic agent usage
Consider TIVA or regional w/ local
Multimodal approaches
Utilize short-acting medications
32
Q

Post-operative Cognitive Dysfunction

A

Increased concern in elderly

No clinically significant association b/w major surgery & anesthesia w/ long-term cognitive dysfunction

33
Q

Emergence Delirium

A 
Pediatrics
More common w/ Sevo & Des
Potential to cause injury & delay discharge
Preventative measures
- Quiet, stress-free environment
- Medication adjuncts
34
Q

Cardiovascular Effects

A

All volatile inhalational agents ↓ CO
↓ MAP secondary to ↓ SVR (vasodilation)
Utilize N2O ↑SVR in combination to decrease
Heart rate changes via SA node antagonism, baroreflex activity modulation, & SNS activity

35
Q

Reverse Robin Hood

A

Steal blood flow from ischemic areas and divert to well-perfused
Vasodilation ↓SVR in hypotensive patients
*Isoflurane (dilates coronary arteries)

36
Q

Preconditioning

A

Exposure to mild intracellular events ↓HR ↓BP ↓CO that protect from ischemic injury & reperfusion insult
Pre-conditioned to respond to severe event
Develop “memory”

37
Q

Sensitization

A

Volatile agents reduce catecholamines necessary to evoke arrhythmias
Less common in ASA I & II classifications
Safe epinephrine dosing
10mL 1:100,000 Epi
Halothane

38
Q

Pulmonary Circulation

A

Nitrous oxide causes slight ↑ PVR
Worse in pulmonary hypertension patients (avoid N2O)
Volatile agents ↓ pulmonary artery pressure d/t vasodilation effects
Hypoxic pulmonary vasoconstriction mildly depressed
Isoflurane has greatest effect

39
Q

Respiratory Effects

A

Shallow breaths ↓ TV ↑ RR (not sufficient to offset)
↓ CO2 responsiveness ↑ apneic threshold
Relaxes airway muscle & produces bronchodilation

40
Q

Renal Effects

A

↓ renal SVR ↓ GFR ↓ UOP
Desflurane least impact on renal function
Sevoflurane associated w/ risk in renal compromise patients leading to haloalkene Compound A (nephrotoxic)
- Older absorbents CaOH or Lithium OH
- Do not exceed 2 MAC hours at flow < 2L/min (another dogma)
- Fresh gas flow < 1L/min not recommended

41
Q

Hepatic Effects

A

Halothane hepatitis
Trifluoracetyl metabolites binding to proteins & forming anti-trifluoracetyl protein antibodies
Repeat exposure antibodies mediate massive hepatic necrosis
Potentially lethal
No longer use Halothane d/t metabolism & potential to impair hepatic function

Current volatile agents - significant liver damage extremely rare
Molecular structure fluorination resists hepatic degradation
No significant impact on hepatic flow

*Sevoflurane 5-8% metabolism

42
Q

Neuromuscular Effects

A

All volatile agents produce dose-dependent skeletal muscle relaxation (areflexia)
Additive effect w/ NMBDs - potentiation
↓ 25-50% dose when compared to TIVA
Delay non-depolarizing NMBD recovery

43
Q

The Ideal Anesthetic Agent

A
  1. Non-irritating
  2. Rapid induction & emergence
  3. Chemically stable (not flammable)
  4. Produce amnesia, analgesia, & areflexia
  5. Potent concentration
  6. No metabolism - excreted by respiratory tract
  7. Non-toxic & no allergic reactions
  8. Minimal systemic changes
  9. Uses standardized vaporizer
  10. Affordable
44
Q

Inhalational Agent Physical Properties

A

Affect how agents work:

Vapor pressure
Boiling point
Partial pressure
Solubility

45
Q

MAC Awake

A

Minimum alveolar concentration when 50% population opens eyes to command
Amnestic w/out analgesic or areflexic

46
Q

MAC BAR

A

Block adrenergic response
Usually 1.3 MAC
Reduce w/ administering narcotic prior
Closer to ED95

47
Q

MAC Unaffected by

A

Gender
Anesthesia duration
Comorbidities

48
Q

Increase MAC

A 
Hyperthermia
Drug-induced ↑ CNS activity
Hypernatremia
Chronic alcohol abuse
Red-haired females
49
Q

Decrease MAC

A 
Hypothermia
Increasing age 6% decline each decade after 40yo
Alpha 2 agonists
Acute alcohol ingestion
Pregnancy
Hyponatremia
50
Q

Vaporizers

A

Volatile agents delivery device
Facilitate anesthetic movement from machine to the patient through fresh gas flow, pressure, & temperature
Calibrated for specific agents

51
Q

ISOFLURANE

A

Halogenated methyl ethyl ether
Most potent current volatile agents
Slower onset & recovery - most soluble blood:gas
Minimal cardiac depression & preserves carotid baroreceptors
Dilates coronary arteries - reverse Robin Hood concern
Pungent not used for inhalational induction
Tachypnea less pronounced
Most stable & consistent

52
Q

DESFLURANE

A

Least potent volatile agent
Rapid induction & emergence
Boiling point close to room temperature
Overpressurizing not recommended d/t ↑HR ↑BP
Pungent - airway irritation, increased salivation, breath holding, coughing, laryngospasm, not used for inhalational induction
Avoid in patients w/ reactive airway disease

53
Q

SEVOFLURANE

A

Fluorinated methyl isopropyl ether
Moderate potency - rapid induction & emergence
Prolong QT interval
CO less maintained than other volatile agents
No heart rate increase/compensation
Non-pungent preferred volatile for inhalational induction

54
Q

Sevo Metabolism

A

CYP450 2E1
5-8% metabolism
Increased inorganic fluoride ions
Only volatile agent metabolized

55
Q

Compound A

A

Sevoflurane absorbent soda lime potential to degrade into Compound A
Increased gas temperature, low flow anesthesia, high Sevo concentrations, & prolonged surgeries
Nephrotoxic?
Safety - utilize CaOh absorbent, flow 2L/min, avoid in patients w/ renal dysfunction
Dogma*

56
Q

Nitrous Oxide (N2O)

A 
Not volatile anesthetic
Colorless & odorless
Non-explosive & non-flammable
NMDA receptor antagonist 
Lower chronic pain risk after surgery
57
Q

N2O PD

A 
Stimulates SNS
Cardiovascular stability
↑ RR ↓ hypoxic drive
↑ CMRO2 ↑ CBF
↑ PONV risk
58
Q

N2O Contraindications

A

Absolute:
Methionine synthase pathway deficiency
Gas-filled space expansion

Relative:
PONV risk
↑ ICP
1st trimester (teratogenic effects)
Pulmonary hypertension
>6hr surgery
59
Q

Xenon

A 
Girl of the 21st century
Ideal inhalational agent
Nobel gas w/ known anesthetic properties
Colorless & odorless
Non-flammable
Inert does not form chemical bonds
MOA via NMDA & glycine receptor binding sites
Minimal CV, hepatic, or renal effects
Neuroprotective?
No ozone layer effect
Cost & limited availability
60
Q

Malignant Hyperthermia

A

Pharmacogenetic disorder triggered by volatile anesthetics, succinylcholine, stress
Ryanodine receptor gene mutation (chromosome 19)
S/S: ↑CO2, muscle rigidity, tachycardia, tachypnea, metabolic acidosis, ↑temp (late sign)

61
Q

Dantrolene Sodium

A

Muscle relaxant
1mg/kg up to 10mg/kg
20mg per vial
Admin until S/S subside

62
Q

Ryanodex

A 
New IV formulation to prevent & treat
Fewer vials & less reconstitution
Shorter half-life
Mannitol supplementation
2.5mg/kg

N926 Pharmacology (17 decks)

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