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Anatomoy 3 > Pharmacology 4 Volatile Agents > Flashcards

Pharmacology 4 Volatile Agents Flashcards

1
Q

Why worry about Anesthesia?

A

BC we give muscle relaxants, which abolish pt’s ability to let us know if they are light - possibility of pt being immobile w normal VS and fully aware but unable to let you know

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2
Q

Ideal VA

A

Rapid onset, rapid and predictable recovery, no residual effects on organs, easy to administer, high safety margin

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3
Q

Woodbridge’s definition of Anesthesia 1950

A

GA is depression of sensory, motor, reflex, and mental fxn.

Analgesia, skeletal muscle relaxation, freedom from reflexes, unconsciousness (hypnosis and amnesia)

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4
Q

Prys-Roberts’ definition of Anesthesia 1970

A

As a result of drug-induced unconsciousness, a state in which the pt neither perceives nor recalls unpleasant stimuli. Increasing dose produces pattern of suppression of responses (somatic easier than autonomic)
Pain - mvmt - breathing - bp/hr - sweating - stress response

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5
Q

Eger’s definition 2002

A

2 qualities apply to VA:
Immobility - what surgeon wants
Amnesia - what pt wants
(reflex suppression and MR are useful, but have nothing to do with anesthetic state, pt can’t tell us anything if amnesia is present)

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6
Q

Stage 1

A

Analgesia and sedation

  • eyes open to command, breathe normally, tolerate mild pain (suturing)
  • airway protective and other reflexes intact
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7
Q

Stage 2

A

Excitement
-rarely see (induction masked d/t IV agents, emergence quick d/t low solubility of VA)
-Muscle mvmt, retching, heightened laryngeal reflexes, disconjugate pupils, increased HR/BP and VE
-Associated w MACawake and amnesia
MACawake = responds to commands but won’t remember

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8
Q

Stage 3

A

Surgical anesthesia

  • associated w MAC
  • no mvmt in response to surgical stimuli
  • no behavioral pain response
  • amnesia
  • reflex depression
  • skeletal muscle relaxation
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9
Q

Stage 4

A

Medullary depression (OD)

  • CV collapse (decreased BP/CO
  • Respiratory collapse (apnea)
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10
Q

Gauging depth - clinical signs - Respiratory

A

-increased depth of VA = increased RR, decreased tidal volume “pant like puppies”
-Changes in character of spontaneous breathing
~excessive depth = rocking boat d/t diaphragmatic breathing only, loss of ICM
-Hard to use in controlled ventilation, NDMR, and opioids

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11
Q

Gauging depth - clinical signs - Eyes

A

-Lacrimation, eye mvmt, disconjugate = light
-Pupils have no direct relationship: opioids = miosis, except meperidine causes mydriasis
mydriasis = increased paCO2 or cerebral hypoxia
all abolished by anti-Ach

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12
Q

Gauging depth - clinical signs - Motor

A

Active expiration = light

Soft abdomen = deep

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13
Q

Gauging depth - electronically - BIS

A

Bispectral Index Monitoring

  • scale of 0 - 100
  • at 60 return to responsiveness
  • Doesn’t work w KETAMINE or N2O
  • NOT a standard of care per ASA or AANA
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14
Q

ASA Practice Advisory on assessing for increased risk of awareness 2005 - Pre-op Eval

A

*review medical records:
-substance abuse
-previous hx of awareness
-hx or anticipated difficult intubation
-chronic pain pts on high doses of opioids
-ASA status of IV or V
-limited hemodynamic reserve
*Interview pt:
-level of anxiety
-other potential risk factors
>cardiac, c/s, trauma, ER, paralysis, use of
MR, N2O, opioids

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15
Q

ASA Practice Advisory on assessing for increased risk of awareness 2005 - Pre-induction phase

A

Adhere to checklist protocol for anesthesia machines and equipment, verify fxn of IV access, pumps, connections
use benzo pre-op

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16
Q

” “ “ - Intra-op monitoring

A
  • Clinical techniques
  • Conventional monitoring
  • Brain fxn monitoring
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17
Q

Gauging depth - electronically - Gas analysis

A

End-tidal agent - monitoring standard

  • dial setting
  • inspired VA
  • expired VA
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18
Q

T or F: Accuracy is most difficult and critical after induction and before incision?

A

True : why?
Too much VA = hypotension d/t lack of stimulus (incision) and vasodilatory effect of VA
Too little VA = salivate, tachycardia, HTN and mvmt on incision

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19
Q

When is inspired amt of VA more than expired?

A

Beginning of the case

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20
Q

What does halogenation do to an agent?

A

Decreases flammability

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21
Q

Using only Fluorine yields what kind of agent?

A

Non-flammable, low solubility, and extreme resistance to metabolism

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22
Q

What current VA degrades in soda lime?

A

Sevo

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23
Q

What VA has the fastest onset?

A

Des < N20 < Sevo < Iso

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24
Q

Lower solubility in blood yields:

A
  • rapid induction
  • more precise control
  • favor prompt recovery
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25
What VA is the cheapest?
Iso at 10 cents per ml
26
What VA is the most expensive?
Sevo at 61 cents per ml
27
N2O
Vapor pressure: its a gas, there isn't one BGPC: 0.46 (fast onset) MAC: 104
28
Iso
VP: 240 BGPC: 1.46 (longest next to enflurane) MAC: 1.17 % (most potent next to N2O)
29
Des
VP: 669 BGPC: 0.42 (fastest onset) MAC: 6.6 % (least potent)
30
Sevo
VP: 170 BGPC: 0.69 MAC: 1.8 %
31
Which VA needs a heated vaporizer? Why?
Des bc Vapor pressure is 669
32
What structures do Iso, Des, and Sevo have?
Iso - halogenated methyl ethyl ether w Cl- Des - Completely fluorinated methyl ethyl ether, replacing Cl- on Iso w Fl- Sevo - Completely fluorinated methyl isopropyl ether
33
If the VA has a low MAC value...
the more potent the agent
34
Which agent is not stable in soda lime?
Sevo, degrades into Compound A
35
Which agent is the only inorganic compound?
Nitrous oxide (N2O)
36
In what 2 ways is nitrous oxide used?
Alone for sedation or in combination w opioids and VA to enhance GA
37
Is N2O flammable?
No, but supports combustion
38
What are advantages of N2O?
* low solubility so rapid on/off * doesn't depress BP * analgesic (10mg of morphine) * additive MAC w VA
39
What are disadvantages of N2O?
*supports combustion *minimal skeletal muscle relaxation *causes PONV *high volume of absorption *decreases immunity r/t ↓ in PMNs *causes miscarriages r/t ↓ methionine synthetase *causes polyneuropathy and B12 inactivation = pernicious anemia
40
N2O is contraindicated in what surgeries?
Some eye surgeries, pneumothorax, belly cases
41
What VA is an organic alkane?
Halothane
42
Why was is taken off of the market?
20% metabolized by the liver = halothane hepatitis
43
What agents are Ethers?
Iso, Des, and Sevo
44
Iso characteristics
* gold standard * most potent w MAC of 1.17% * longest onset/offset w solubility of 1.46 * pungent, so no inhaled induction * extreme physical stability
45
Des characteristics
* Least potent w MAC of 6.6% * need heated vaporizer d/t vapor pressure of 669 * boils near room temp * more stable and resistant to metabolism than iso * the most rapid onset/offset w solubility of 0.42 * expensive * pungent * carbon monoxide generation in soda lime
46
Sevo characteristics
*MAC of 1.8% *solubility of 0.69 *non pungent *most expensive *metabolism 5% potential nephrotoxicity *degrades in soda lime to compound A = No FGF < 1 L/min and no 2 MAC hours a low flow
47
Name brand names for agents
``` Iso = Forane Des = Suprane Sevo = Ultane ```
48
MAC values for VA's are additive
True
49
What are the factors that decrease (modify) MAC?
Opioids - decrease MAC significantly Age - decrease MAC with age Hypothermia, hyponatremia Pregnancy, Lidocaine, Alpha-2 agonist
50
What are some factors that increase MAC?
Hyperthermia, Drugs that ↑ CNS (cocaine, MAIOs, anxiety), hyperthermia, hypernatremia
51
What is VA MOA?
unknown | mediated at cord, supraspinally, RAS likely
52
What is the Meyer-Overton theory?
correlation btw lipid solubility (oil:gas partition coefficient) and VA potency causes distortion of ion channels, AP blocked
53
Unlikely that voltage-gated channels plan a role in production of anesthetic state
True
54
What is the effect on ligand-gated channels?
Glutamate, glycine, and GABA may be important site (role)
55
What are the effects of VA's on CNS?
*No retrograde amnesia *No prolonged effects *Luxury perfusion - ↑ CBF and ↓ CMRO2 (risk of ↑ ICP w tumors so hyperventilate, ↓ CO2 to ↓ vasodilation
56
What are the effects on EEG?
< 0.4 MAC = VA ↑ freq + voltage 0.4 MAC = shift post to ant, ↓ CMRO2, + amnesia 1 MAC = freq ↓ + max voltage 1.5 MAC = burst suppression 2 MAC = silence/isoelectric No sz activity (fast freq + high voltage = spikes
57
How does VA effect EP's?
↓ amplitude + ↑ latency * Don't go above 1 MAC * Don't go up and down * Usually asked to avoid N2O
58
At what MAC does cerebral vasodilation occur?
> 0.6 MAC
59
At what MAC is cerebral autoregulation best preserved?
at 1 MAC
60
Do VA's including N2O enhance CSF production?
No, they ↑ reabsorption and ↑ CSF pressure
61
What are the effects of VA's on MAP and how are they produced?
current VA's ↓ MAP by ↓ SVR (vasodilate) *not N2O* so use some N2O w VA to ↓ drop in MAP
62
What are the effects of VA's on HR from greatest to least?
They ↑ HR - Iso > des > sevo | The more rapid the rise on conc, the more rapid the increase in HR
63
What are the effects of VA's on RAP?
Des, Iso, and N2O ↑ RAP while sevo ↓ RAP
64
What are the effects of N2O on PVR?
↑, more pronounced if pre-existing pulm HTN and neonates, congenital heart dz R to L shunt
65
Describe a spontaneously breathing pt w VA's
Higher HR, Lower CO, SVR, BP d/t higher levels of CO2 (vasodilator) and SNS stimulation
66
What is coronary steal, what VA does this, and what must be done in CAD pts?
coronary vasodilation and blood is diverted away from ischemic areas, Iso does this In CAD pt, no ↑ HR or drop in BP
67
How do you control Des and Iso neurocirculatory responses?
Don't stomp on the gas! slower increase in VA, use fentanyl, esmolol, precedex or clonidine
68
List cardiac coexisting dz's and choices of VA:
CHF - no VA, use N2O and fent CAD - Sevo and fent Valvular HD - VA good for regurg (full, fast, forward) VA contraindicated in stenosis!!! Use N2O
69
What are the 3 prominent effects of VA's on ventilation?
1. Pattern of breathing (↑ RR, ↓ VT) = rapid shallow 2. ↓ Ventilatory response to CO2 and hypoxemia (quality of each breath ↓, so dead space ↑) 3. ↑ Airway resistance (bronchodilator once alseep)
70
Why does pt on vent need great VT?
VT augmented bc VQ mismatch, ↓ FRC, ↑ dead space (d/t lack of diaphragmatic vent) So assist spontaneous breathers... LMA's
71
What is the response to hypoxemia in VA?
0. 1 MAC depresses this by 50-70% | 1. 1 MAC abolishes response completely
72
All VA's including N2O ↓ FRC
True
73
What are VA hepatic effects?
Maintain hepatic BF and venous O2 saturation
74
What agents have metabolites?
Iso and des have trifluoroacteic acid but remember, des has almost NO metabolism Sevo produces hepatotoxic compound A
75
VA produce dose-related decreases in:
* Renal blood flow * GFR * Urine output (d/t ↓ BF)
76
How do you abolish or lesson these effects?
Pre-op hydration
77
How is Compound A formed?
When Sevo degrades in CO2 absorbent
78
What makes the degradation of sevo worse?
Dry granules, higher absorbent temps
79
What is important to remember about the flow of Sevo?
Never use with FGF < 1 L/min, do not exceed 2 MAC hours at 1-2 L/min FGF
80
What are the effects of VA's on skeletal muscles?
Produce some skeletal muscle relaxation Potentiate MR's N2O does not do either!
81
What about MH?
All VA's and Succs can trigger MH, but NOT N2O
82
What are the obstetric effects of VA's?
↓ in uterine BF and uterine smooth muscle tone modest at 0.5 MAC, substantial at 1 MAC N2O does NOT do this
83
What is a good cocktail for C/S?
0.5 MAC VA + 0.5 MAC N2O
84
Do VA's cross the placenta?
Yes, but rapidly exhaled after birth
85
What do VA's do to the resistance of infection?
All but N2O > VA's inhibit WBC chemotaxis
86
What are the genetic effects of VA's?
*Not mutagens or carcinogens (-Ames test) *N2O ↑ abortion/miscarriage (B12 enzyme methionine synthetase decreased)
87
How do VA's work w bone marrow fxn?
N2O > 24 h = megaloblastic changes N2O > 4 d = agranulocytosis Can still give to bone marrow recipients Avoid in burns/immune depressed = repeated exposure have cumulative effects
88
N2O and peripheral neuropathy
Long exposure = nerve degeneration sensorimotor polyneuropathy pernicious anemia
89
What do VA's do to total body O2 needs?
VA decrease VO2
90
What makes VA's resistant to metabolism?
Fluorine-carbon bond
91
What is the % of Iso metabolism?
0.2%
92
What is the % of Des metabolism?
0.02%
93
What is the type of metabolism that they undergo and what metabolite do they have in common?
Oxidation by cytochrome P450 | Trifluoroacetic acid
94
Carbon monoxide toxicity:
Des >> Iso DEGRADATION Caused by strong bases (KOH and NaOH) Can not detect intraop Cause CNS disturbances
95
What factors favor carbon monoxide?
Dry absorbent (prolonged high FGF) High absorbent temp (low FGF) baralyme > sodasorb
96
Metabolism of Sevo:
2-5% oxidation by cytochrome P450
97
Degradation of Sevo and causes:
produces compound A * high absorbent temps * dry absorbent * baralyme >> soda lime
98
Des compensation is used on the Fabius GS bc:
Des has characteristics that affect the sensitivity of the Fabius GS flow sensor
99
If this is not done, what will happen?
VT readings will be higher than set VT (up to 25%)
100
List physical signs of adequate ventilation in an anesthetized pt:
*chest mvmt * BBS * mvmt of bag/bellow * mvmt of unidirectional valves * sounds of vent * moisture in ETT w exhalation
101
List monitors that display signs of adequate ventilation in an anesthetized pt:
*Oxygen analyzer * spirometry * airway pressure * exhaled volume on monitor * gas analysis * capnography
102
What are common problems w spirometry?
weight/bulk close to face tubing disconnections/damaged peds vs adult D Lite sensor
103
List common problems w mechanical ventilation:
* Failure to resume or failure to initiate | * **Disconnection*** most common - Y piece -
104
How to prevent these problems from occurring:
* Pre-anesthesia checklist * Precordial * If you turn off vent, keep your finger on the switch * Use apnea alarms and DON'T silence them
105
List the umpteen mechanisms of circulatory effects of VA -
* direct myocardial depression * decreased SNS * peripheral autonomic ganglionic block * decreased carotid sinus baroreceptor activity * decreased cAMP * decreased release of catecholamines * decreased calcium ion influx thru slow channels
106
N2O alone or w VA produces mild SNS stim:
increased, plasma catecholamines, mydriasis, increased body temp, diaphoresis, increased RAP, systemic and pulmonary vasoconstriction
107
N2O w opiates:
more circ depression | decreased bp, co, increased lvedp and svr
108
High risk factors for PONV:
3 pts; hx, gyn, breast
109
Medium risk factors for PONV:
2 pts: face, ear, neuro, obesity, cross eyed
110
Low risk factors for PONV:
1 pt: young, female, anxiety, lap chole, opioids given, case > 1 hr
111
What determines FGF:
the vaporizer and flow meter settings
112
What determines FI
FGF, circuit vol, circuit absorption
113
what determines FA
uptake, ventilation, and conc and second gas effects
114
what determines Fa
V/Q mismatch
115
Why do we use PA as a measure of depth?
bc Pbr = Pa = FA
116
Why is solubility important?
The more poorly blood soluble agent has a faster speed of induction
117
What is a time constant and what are the %?
``` Capacity / flow 1 = 63% 2 = 86% 3 = 95% There is circuit, lungs, and brain ```
118
Uptake =
BGSC x Content (A-V) x Q (CO)
119
The higher the uptake....
the slower the induction
120
High FA/FI ratio =
less difference btw inhaled and exhaled VA
121
The VRG is how much % of body wt and how much % of CO?
10 % body wt and 75% CO
122
What organs are in the VRG?
Brain, heart, liver, kidneys
123
The greater the VAlv / FRC ratio...
the faster induction | 5:1 in neonates as compared to 1.5/1 in adults
124
What cases would it be wise to avoid N2O?
abdominal, bowel, craniotomies, sitting positions, anytime the wound is higher than the heart
125
The greater the A-V difference of VA...
the slower the rate of rise/slower induction

Anatomoy 3 (9 decks)

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