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Inhaled Anesthetics Flashcards

1
Q

Atomic Number

A

Protons + neutrons - both carry weight

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2
Q

Ionic v Covalent bonding

A 
ionic = complete loss of electron (NaCl) 
Covalent = shared e- , can be polar (non-equal sharing, a relative charge on one side) or polar
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3
Q

Forms of Inhaled anesthetics

A

non-organic (no carbon) - NO, xenon
organic
alkane
ether R-O-R

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4
Q

Molecular structure of inhaled anesthetics

A

covalent bonds.

physical characteristics determined by molecular structure - solubility, boiling point, vapor pressure

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5
Q

Vapor Pressure

A
  1. the pressure exerted by a gas above its liquid phase at atmospheric pressure
  2. the max pressure it can exits as both a liquid and gas at standard conditions.
  3. determines the max concentration a gas can be under standard conditions
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6
Q

the effect of temperature on vapor pressure

A

increasing temp = increased vapor pressure

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7
Q

3 Gas Laws

A

Boyles: P1V1 = P2V2 (pressure & vol are inversely related at std temp)

Charles: V is directly related to T (constant P)

Gay-Lussacs: P directly to T (constant V)

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8
Q

Avogadros Law

A

the gram molecular weight of an ideal gas at standard temp is occupies 22.4L and contains 6 x 10^23 particles

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9
Q

Action of an Inhaled Anesthetic depends on what?

A

therapeutic tissue concentration in CNS

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10
Q

Induction Goal

A 
reach equilibrium (the gas exerts the same partial pressure on either side of the membrane, there is no net movement) Fi/Fa = 1. 
does NOT mean equal number of molecules.
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11
Q

What factors effect reaching equilibrium?

A

solubility - less soluble quicker
CO - lower CO quicker
fresh gas flow
minute ventilation

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12
Q

Three Factors of getting the gas from vaporizer to alveoli

A
  1. partial pressure gradient
  2. effect of alveolar ventilation
  3. the time constant - if unopposed (no uptake) the rate is determined solely by this (capacity/flow L/L/min)
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13
Q

Time Constants & % Change

A

0.7 TC = 50%
1 TC = 63%
2 TC = 86%
3 TC = 98

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14
Q

Factors Affecting Inspiratory Concentration

A

FGF rate
Circuit volume/absorption
gas concentraion

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15
Q

3 Factors that affect uptake of an inhaled anesthetic

A
  1. solubility
  2. pulmonary blood flow (CO)
  3. partial pressure difference
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16
Q

How uptake effects the Fi:Fa ratio

A

uptake prevents alveolar concentration from rising. Fi/FA <1. means a slower onset - the partial pressure doesn’t build up (alveolar PP determines blood PP which determines brain PP)

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17
Q

Solubility of a Gas

A

lower solubility = less uptake = faster onset
expressed by a b/g coefficient.

a lower b/g coefficient means lower solubility.

18
Q

B/G Coefficient

A

the ratio of the concentrations of the anesthetic gas in each of two phases at steady state - equal partial pressures in the two phases.

Ex: desfluranes b/g is 0.42 meaning 1ml of blood contains 0.42 as much desflurane as 1 ml of alveolar gas

19
Q

B/G Coefficients of Common Inhaled Anesthetics

A 
Des : 0.42
NO: 0.47
Sevo: 0.65
Iso: 1.4 
Enflurane: 1.9 
Halothane: 2.4 
Methoxy: 15
20
Q

Fat Solubility of a Vapor.

A 
potency is directly related to the fat/blood coefficient. highest fat solubility = lowest MAC. 
All agents (except N2O) have significant fat solubility.
21
Q

Partial Pressure effect on uptake

A

greater gradient = more uptake

22
Q

Uptake into Tissue Groups

A

determined by solubility, blood flow, and partial pressure gradient.
1- vessel rich (most perfusion & CO)
2- muscle
3- fat - very high solubility = a capacity that takes days to fill
4- vessel poor

23
Q

Ventilation Effect on Uptake

A

increased ventilation constantly replaces alveolar concentration to increase partial pressure quicker. effect more noticeable with highly soluble agents that have greater uptake. with insoluble has minimal effect - these agents already reach a FA/Fi ratio of 1 quickly

24
Q

Elimination of Anesthetics

A

primarily via exhalation. minimal biotransformation and insignificant transcutaneous.

Recovery is usually faster than induction unless prolonged anesthesia. this is due to continued uptake by tissues that have not yet reached steady state which helps drop alveolar partial pressure

25
Q

Speeding Recovery/Elimination of Anesthetics

A 
eliminate rebreathing 
high FGF 
low circuit volume/absorption
low solubility 
high CBF 
increased ventilation
26
Q

Maintenance of Anesthesia

A

after induction only the tissue uptake requires constant replacing. flow rates reduced to maintain steady state.

27
Q

What slows emergence?

A

high BMI, highly soluble agents, long anesthesia time

28
Q

MAC awake

A

1/3 MAC concentration - hypnosis but may move

29
Q

Receptors of inhaled anesthetics

A

Glycine - on spinal cord inhibits movement

GABA - hypnosis (supraspinal)

30
Q

Inhibitory Effect of Inhaled Anesthetics

A

presynaptic - enhances basal GABA release
post-synaptic - potentiates ligand gated ion channels activated by GABA & glycine
extra-synaptic: enhance GABA receptors & leak currents

31
Q

Excitatory Effect of Inhaled Anesthetics

A

suppress excitatory transmission
pre-synaptic - reduce glutamate release
postsynaptic - inhibitors excitatory inotropic receptors stimulated by glutamate

32
Q

General Anesthesia

A

an altered physiologic state characterized by reversible LOC, analgesia, amnesia, and some degree of muscle relaxation

33
Q

Theories of Anesthesia Action

A

multiple ion channels involved
a reduction of nerve transmissions
inorganic agents inhibit NMDA
binding to hydrophobic sites in neuronal membrane expands phospholipid bilayer altering membrane function

34
Q

Unconsciousness

A

cerebral cortex & thalamus

35
Q

amnesia

A

amygdala & hippocampus

36
Q

analgesia

A

spinothalamic tract

37
Q

immobility

A

spinal cord receptors

38
Q

What decreases MAC?

A
  • Age
  • Anemia
  • Hypothermia
  • Drugs: sedatives, narcotics, alpha agonists, lithium
  • Hypoxemia
  • Hyponatremia/hypercalcemia
  • Pregnancy
  • Extreme hypercarbia
  • Acute ethanol/drugs – except cocaine

all animals have days having happy picnics eating apples

39
Q

what increases MAC?`

A
  • Youth
  • Hyperthermia
  • Hyperthyroidism
  • Hypernatremia
  • CNS stimulants – cocaine & amphetamines
  • Red Hair
  • Chronic ethanol
40
Q

Guedels Stages of Anesthesia

A

I: awake, amnesia, analgesia. Induction - loss of consciousness
II: excitation. from LOC to automatic breathing. eyelash reflex lost
III: surgical anesthesia. automatic breathing to respiratory paralysis.
IV: loss of life sustaining reflexes. respiration cessation to death.

41
Q

Major risk of inhalation anesthetics?

A

ALL are MH triggers

42
Q

Organ Effects of Inhaled Anesthetics?

A 
Cardiac: decrease BP, CO, SVR. HR up or down. 
Resp: rate increase, TV decrease
Cerebral: BF increase, CMRO2 decrease
NM: relax
Renal: decrease BF and GFR
Hepatic: decrease BF 
Metabolism slight decrease

Pharm (11 decks)

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