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Anesthesia Orientation > Inhaled Anesthetics > Flashcards

Inhaled Anesthetics Flashcards

1
Q

Toxicity of sevoflurane?

A

Compound A - more likely with low FGF, inc [sev] inc canister temp, dec water content, inc freshness of absorbent (compound A causes nephrotoxicity in rats - not exactly proven in humans but can see some transient effects on the kidneys)

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2
Q

Which volatile anesthetics and conditions produce CO2?

A 
Des > Isf > Sevoflurane
dry absorbents
high temp in absorbents
high [des]
Baralyme > soda lime
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3
Q

Value of MAC awake

A

O.3

Eg MAC of Iso is 1. 1 x 0.3 = 0.3

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4
Q

what properties of an anesthetic make it quick on and off

A

dec blood/gas solubility

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5
Q

MOA of inhaled anesthetics

A

act at ion channels in CNS and PNS to potentiate inhibitory pathways (GABA, glycine) and inhibit excitatory pathways (NMDA)

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6
Q

relationship b/w lipid solubility and potency

A

inc lipid solubility will increase potency (remember the brain and spinal cord are largely lipid so the inhaled agent that is lipid soluble will quickly get to the brain and spinal cord)

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7
Q

what is MAC pertaining to inhaled anesthetics

A

the % of alveolar concentration at which 50% of patients will not move to surgical incision

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8
Q

MAC % of Sevo

A

about 2

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9
Q

MAC % of Des

A

6

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10
Q

MAC % of Iso

A

1

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11
Q

what is MAC aware?

A

about 0.6 (vs awake is 0.3)

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12
Q

relationship b/w potency and MAC %

A

higher the potency, the lower the MAC%

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13
Q

what types of conditions decrease MAC %

A

pregnancy, acute alcohol, hypothermia

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14
Q

what types of conditions increase MAC %

A

chronic alcohol, acute meth, hyperthermia, hypernatremia. nb thyroid dz will not affect MAC

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15
Q

what is typical BIS range desired during anesthesia

A

40-60 (most say < 50)

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16
Q

how does MAC % relate to partial pressures

A

multiply MAC% by atm mmHG to find out what partial pressure is.
e.g. for Iso Mac is 1.2% x 760 mmHg = 9 mmHg is MAC

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17
Q

why is des heated and pressurized?

A

has a high vapor pressure. (heating would normally inc vp but with des it’s pressurized which would promote cooling/condensation so it has to be heated. net effect is still that the heating + pressure lowers the vapor pressure so we can deliver set amounts to the pt)

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18
Q

why does the anesthesia machine need to pump some fresh gas flow around the vaporizer?

A

b/c the vp of all the inhaled agents at room temperature is higher than the MAC % that we want to deliver to pts (eg Sevo vp is 157 mmHg which is 21 % of atm pressure. MAC of sevo is only ~ 2% so we need to divert a lot of fresh gas around the vapor so we only deliver 2% vs 21% to the pt)

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19
Q

which inhaled agent has the lowest blood/gas solubility (aka which is fastest on and off agent)

A

Desflurane

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20
Q

anesthetic agent where correlates with the rate of onset of anesthetic state

A

rate of rise of partial pressure of agent in the alveolus (NOT blood) correlates with rate of onset of anesthetic state

21
Q

how can i increase the alveolar partial pressure of an inhaled agent faster (3-4)

A

inc alveolar ventilation
inc inspired concentration
second gas effect
system

22
Q

how to increase the rate at which inhaled anesthetics are eliminated

A

inc cardiac outpot
inc solubility in blood
inc v/q mismatch
lave a-v partial pressure differencse

23
Q

how is anesthitic eliminated/metabolized

A
  • most expired via lungs unchanged

- small bit metabolized via P-450 (most metab is SEVO)

24
Q

most irritating inhaled agent to the aw

A

desflurane (may activate sympathetics)

25
Q

most potent inhaled agents

A

Iso > sevo > des

1% 2% 6%

26
Q

what can happen if you quickly increase Des or Iso concentrations

A

cardiovascular stimulation (may be less in neonate and geris)

27
Q

effect of volatile anesthetics on CV system

A
  • negative inotropy (dec strength of mm contraction) ↓ CO
  • HR: des> iso >sevo may inc HR BUT w/concurrent opioids there’s little effect
  • iso, sevo, des ↓ SVR by arterial vasodilation (via B stimulation) and ↓ CO (no expected compensation from normal svr to co relationship) so ↓ BP
28
Q

if pt has LQTS how will you proceed with inhaled anesthetic

A

inhaled agents (esp SEVO) can prolong QT so can still use on these pts but smart to treat with bblockers

29
Q

effect of volatile anesthetics on resp system

A
  • all gases ↑ RR & ↓ TV overall ↓ min vent; depresses hypoxic drive
  • all gases ↓ hypoxic drive/↑ apneic threshold (blunt response to hi CO2 and low O2)
  • Iso > Sevo is a bronchodilator (may irritate upper airways) and ↓ HPV
  • PVR: volatile gases ↓ but N2O ↑
30
Q

effect of inhaled agents on CNS (CBF, ICP, CMRO2)

A
  • all gases dilate cerebral blood vessels -> inc CBF -> inc ICP (predominate effect when > 0.5 MAC) (iso least potent) n.b. hypocapnia can counteract ↑ICP)
  • all gases put pt to sleep so ↓ CMRO2 (predominate effect when < 0.5 MAC
  • depress/slowed EEG: anesth induction inc freq and amplitude of EEG waveforms. At 1 MAC EEG slows. Burst suppression (isoelectric) w/sevo or iso @ 2 MAC)
  • all agents inc latency and dec amplitude of evoked potentials at > 1 MAC
31
Q

how do volatile anesthetics affect NMB

A

potentiate effects of both sux and non-depolarizing as they relax skeletal mm

32
Q

which agents trigger MH

A

inhaled anesthetics and sux can both do it

33
Q

5 things to dx MH

A

1) inc ETCO2
2) tachycardia
3) mm rigidity
4) temp inc
5) respiratory acidosis

34
Q

which agent is most irritating to aw; least?

A

desflurane

sevo is least

35
Q

how NO affects CV

A

stimulates release of endogenous catechols; depresses heart contractility, inc pulm vasc resistance

36
Q

how NO affects resp

A

inc rrr, dec tv, inhibits hypoxic drive

37
Q

how NO affects CNS

A

inc CBF, inc ICP - don’t use in neuro cases

38
Q

NM effects of NO

A

no relaxation; no MH trigger, may inc PONV

39
Q

what caution must be taken with NO and closed spaces

A

NO will diffuse into them increasing pressure

40
Q

name and explain 3 factors which affect uptake of anesthetic gases

A

1) solubility (determined by blood-gas coeff…less solb is faster b/c it takes less time to “fill up the tank” before levels equilibrate with the brain)
2) CO - ↑ CO -> more blood thru lungs -> more anesthetic removed from the gas phase therefore lower alveolar partial pressure of gas (FA) and slower build up (affects more soluble gases the most)
3) partial pressure difference of gas b/w alveoli and pulmonary vein: more difference encourages gas to go into blood. (V-Q mismatch: inc FA, dec FI; L to R cardiac shunt w/normal tissue perfusion doesn’t affect anesthetic uptake; R to L cardiac shunt: bypassing of blood past the lungs = slower rate of inc in art concentration & slower induction of anesthesia

41
Q

effect of volatile anesthetic on renal fxn

A
  • all gases ↓ RBF (via inc renal vasc resistance), ↓ GFR, ↓ UOP
  • Sevo -> Compound A (occurs @ low fgf rates; nephrotoxic in rats) so use FGF 2L/min
42
Q

effect of volatile anesthetics on hepatic fxn

A
  • all gases ↓ hepatic blood flow

- cytochrome P450 produces trifluoroacetylated protein antigens (moreso w/Iso)

43
Q

effect of volatile anesthetic on hematologic and immune system

A
  • N2O oxidizes B12 so inhibits enzymes requiring B12 (methionine synthetase (myelin) and thymidylate synthetase (DNA))  bone marrow depression (megaloblastic anemia) and neurologic deficiencies (PN)
44
Q

what is significant about 1.3 MAC

A

stops movement in 95% of pts and typically allows intubation (ED95)

45
Q

significance of 1.5 MAC

A

“MAC BAR” - block adrenergic response (nb. opioids and N20 dec MAC BAR)

46
Q

when is MAC highest?

A

3-6 mos old

47
Q

which factors inc MAC?

A
  • amphetamines
  • ephedrine (more catechols)
  • age < 6 mos
  • hyperthermia
  • hyperthyroid
  • hyperNa
  • red hair (FALSE!!!!)
48
Q

which factors dec MAC?

A
  • opioid, benzo, propofol, ketamine, a2-agonist, iv LA
  • acute ETOH abuse
  • inc age > 1 yr
  • pregnancy
  • hypothermia
  • hypoTN
  • hypoxemia
  • anemia
  • metabolic acidosis
  • sepsis
  • lithium
  • verpamil
49
Q

what are the max trace concentrations that NIOSH allows in the OR?

A
  • halogenated agent alone = 2 ppm
  • if combined w/nitrous = 0.5 ppm
  • high exposure (>10 to the third ppm) inc risk of abortion and dec fertility

Anesthesia Orientation (5 decks)

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