Inhaled Anesthetics Flashcards
Has a MAC of 104
Nitrous Oxide
Has a MAC of .75
Halothane
Has a MAC of 1.63
Enflurane
Has a MAC of 1.17
Isoflurane
Has a MAC of 6.6
Desflurane
Has a MAC of 1.80
Sevoflurane
In what anesthetic is a preservative necessary?
Halothane
contains 0.01 (w/w) thymol as a preservative
Has a sweet odor?
Nitrous Oxide
Is not stable in soda lime absorbent?
Halothane & Sevoflurane
Blood:Gas partition coefficient of 0.46
Nitrous Oxide
Blood:Gas partition coefficient of 2.54
Halothane
Blood:Gas partition coefficient of 1.90
Enflurane
Blood:Gas partition coefficient of 1.46
Isoflurane
Blood:Gas partition coefficient of 0.42
Desflurane
Blood:Gas partition coefficient of 0.69
Sevoflurane
669 Vp @ 20C
Des
157 Vp @ 20C
Sevo
238 Vp @ 20C
Iso
243 Vp @ 20C
Hal
SVP Hi-Se
Hal & Iso ~ 240
Sevo & Enf ~ 160
immobilizing effects of IAs involves action on the _____
sedation/hypnosis/amnesia involves actions _______
spinal cord
supraspinal - brain and brainstem
Unconsiousness
glutamate blockade
-cortex, thalamus, brainstem
Amnesia
GABAa
-amygdala, hippocampus
Analgesia
NMDA, K2p & AMPA
-spinothalamic tract
Immobility
Glycine receptors
-spinal cord central pattern generators
SVP of an inhaled anesthetic depends on?
Temperature
Time constants
type of measurement used to determine time to reach equilibration of anesthetic gas between PA and Pbrain
- 1 TC = 63% equilibration
- 3 TC = 95%
- 4 TC = 98%
How to calculate Time Constants
the capacity of the system (L)
/
total flow to the system (L/min)
Recovery depends on?
- solubility, tissue uptake, duration of admin
aka: context-sensitive half time
Effects of a R>L & L>R shunt on Pa of inhaled anesthetics
Right to Left (volatile): slower induction
Left to Right (volatile): little effect on induction
Inhaled anesthetics with increased context sensitive half time?
Halothane and Isoflurane after administration > than 30 min - 1hr.
Des and Sevo only minimally
MAC is a measure of?
Potency
MAC values for multiple co-administered anesthetics are:
Additive
MAC values administered with opioids are:
Synergistic
VA that causes the most airway irritation?
Des
Increases incidence of arrhythmias?
Halothane
-due to decreasing threshold at which catecholamines will cause ventricular ectopy
dysrhythmias occur H > I > D&S
metabolism can lead to hepatotoxicity when using?
Halothane
All around bad for the liver:
halothane hepatitis, hepatocyte hypoxemia, decreased hepatic artery blood flow, and metabolized to a protein that may produce liver injury
CO toxicity is most likely using?
Desflurane
-caused by rxn of CHF2 and the strong bases present in the absorbents
IA general effects: Neuro
- decrease CMRo2
- increase CBF, increase ICP
IA general effects: Pulm
- increase RR and decrease TV, rapid shallow breathing
- bronchodilation & decreased airway resistance
- depress hypercapnia and hypoxia response
IA general effects: CV
-decrease SVR via vasodilation (but preserve CO via reflex increase in HR)
An abrupt and large increase in the delivered concentration of this IA may produce transient increase SBP and HR
Des
-has the most SNS activity
IA associated with nephrotoxic Compound A
Sevo
-no evidence that it produces a level that is nephrotoxic
IA general effects: OB
-all decrease uterine blood flow and uterine contractility (cause uterine relaxation)
IA speculated role in spontaneous abortions?
N20
Max levels of trace gas in atmosphere
Halogenated alone: 2 ppm
Nitrous alone: 25 ppm
Combo: Nitrous 25 ppm + Halogenated 0.5 ppm
IA general effects: Renal
-decrease renal blood flow, GFR, urine output
IA general effects: Hepatic
-decrease hepatic blood flow and O2 delivery
the anesthetic with the possible complication: inhibits methionine synthetase
N20
the anesthetic with the possible complication: metabolism results in free fluoride ions in the blood
sevo
the anesthetic with the possible complication: may result in junctional rhythm or AV nodal dissociation at higher mac doses
iso
dysrhythmias occur H > I > D&S
contraindicated in trauma pts with rib fractures
n2o
best for inhalation inductions
sevo
may cause HTN and Tachy d/t SNS stimulation
des
Contraindicated in neurosurgery
high dose inhalation anesthesia > 1 MAC
-increases ICP
VAs cause a rise in arterial CO2 levels because they slow down the respiratory rate? T/F
false
-decreased TV increased RR
“panting”
-decrease in alveolar min. ventilation
Sevo in an Iso vaporizer, would the actual output be more or less than what it is set at?
Less
Sevo has a lower SVP so the output would be lower
What primarily determines mechanical dead space in a Mapelson circuit?
the FGF rate
What breathing circuit system has complete rebreathing?
Closed circuit system
Which Mapelson circuit has no bag and no APL valve?
E
Best IA for liver failure pts?
Isoflurane
Which of the volatile agents has the least effect on intracranial pressure?
Des
Iso
Sevo
-all the modern inhaled anesthetics
Of the volatile agents which has the greatest potentiation of neural muscular junction blockade?
Des
Metabolism plays an important role on the rate of rise of FA/FI during induction of anesthesia for which volatile anesthetics?
NONE
VA effects on neuromonitoring
EEG - dose-dependent changes in Hz, initially increases, then Hz lowers with higher amplitude, then burst suppression, then isoelectic
SSEP: decreases amplitude and increases latency
MEP: very sensitive to depression by volatile anesthetics. Use TIVA if able.
T/F VAs enhance ischemic preconditioning
True
exposure to a single/brief episode can confer a protective effect on the myocardium against reversible or irreversible injury with a subsequent prolonged ischemia insult - works via mitochondrial ATP sensitive K+ channels
SNS stimulation, order VAs most to least
Des > Iso > Sevo > Hal
N2O also increases SNS stimulation
Gas that increases PONV
N20
These patient factors affect pharmacokinetics of VAs
- aging
- decrease in lean body mass
- increase in body fat
- impaired pulmonary exchange
- reduced CO
-opposite effects in very young
2nd gas effect
ability of high volume uptake of one gas to accelerate the uptake of a second gas due to the resulting higher concentration of the 2nd gas in a smaller lung volume
Concentration effect
the greater the inspired concentration (Fi) the greater the rate of rise (Fa/Fi)
What is the relevance of oil:gas coefficients?
- they parallel anesthetic requirements
- MAC is calculated as = 150 / the o:g
rate of rise VS solubility
Inversely proportional
The more soluble the agent is the slower the rate of rise of PA/Pi (because the blood absorbs more of the agent)
Diffusion Hypoxia
Occurs when inhalation of nitrous oxide is discontinued abruptly which reverses partial pressure gradients which causes N2O to leave the blood and rapidly reenter alveoli - which results in dilution of PaO2 available for arterial blood to absorb resulting in arterial hypoxemia
What is MAC
Minimal alveolar concentration: The concentration of the gas in the lungs that is needed to prevent movement (motor response) in 50% of subjects in response to surgical incision (noxious) stimulus
Rank MAC values from High to Low
N2o 104 Xenon 63-71 Des 6.6 Sevo 1.8 Enflurane 1.63 Iso 1.17 Hal 0.75
MAC required for immobility
2.5-4x MAC (which is a lot)
MAC BAR
“Blunt Autonomic Responses” = BAR
Typically 30-50% greater than MAC
1.3-1.5 MAC or for Sevo 2x MAC
Things that affect the pressure of inspired gas and uptake
- CO
- Blood:Gas solubility
- (PA - PV) = Alveolar to venous partial pressure gradient mm Hg (% gas)
- Bp = barometric pressure mmHg
Why is the uptake of VAs faster in infants?
- higher alveolar ventilation
- smaller FRC
- greater proportion of CO to VRG (brain)
- IAs are less soluble in infants bc they have a higher water content
How does Henry’s Law apply to uptake of anesthetics?
At 37C, the amount of gas that dissolves into the blood is directly proportional to the partial pressure of the gas in contact with the blood.
Think higher partial pressure = higher concentration gradient
What is the Meyer-Overton Correlation
potency of an anesthetic agent is proportional to lipid solubility as measured by its oil-gas partition coefficient
Which anesthetics blunt autoregulation of cerebral vasculature?
- at 1 MAC halothane blunts autoregulation
- des and sevo do not alter autoregulation
- des may at >1.5 MAC)
the anesthetic with the possible complication: emergence delirium in peds
Sevo
T/F VAs induce coronary vasodilation?
True
What is the apneic threshold?
the highest arterial carbon dioxide tension at which a pt remains apneic
it is approximately 4 or 5 mm Hg less than resting arterial carbon dioxide tension achieved during spontaneous ventilation
ex: pt will spont breath at Co2 of 55 but won’t at 51.
What is a possible complication of the bronchodilator effects of VAs?
Inhaled anesthetic agents inhibit HPV (hypoxic pulmonary vasoconstriction) which is a reflex vasoconstriction in the pulmonary circulation in response to a low regional partial pressure of oxygen to reduce V/Q mismatching
VAs could worsen V/Q mismatching if vascular beds are vasldilated
Usually negligible
the anesthetic with the possible complication: MH
-halothane is the most potent trigger of MH, but all VAs can trigger MH
- Xenon can be given safely to a pt with MH
- N2o does NOT trigger MH
Metabolism of Des in a dry Co2 absorber can produce?
can create CO
Biotransformation of ____ produces Free Fluoride Ions
Sevo - but no evidence of renal failure
T/F: VAs enhance the activity of succinylcholine but NOT non-depolarizing NMBs?
False
They enhance both and cause dose related skeletal muscle relaxation
N2o effects on pulmonary vasculature
-increases pulmonary vascular resistance and should be avoided in patients with pulmonary HTN
