Inhalation Agents Flashcards
1
Q
3 most common inhalation anesthetics
A
- Isoflurane
- Desflurane
- Sevoflurane
(N2O, we give often… but not a true anesthetic)
2
Q
Inhalation agents are direct…
A
Myocardial depressants
3
Q
The primary objective of inhalation anesthesia is
A
To achieve a constant and optimal partial pressure of anesthetic administered in the brain
4
Q
The target organ in inhalation anesthesia is the __
A
Brain
5
Q
Equilibrium is referred to as ___
A
Steady state
6
Q
At equilibrium (steady state)
A
Constant and optimal pressure is maintained
7
Q
Partial pressure of a gas are…
A
Equal in both the blood and the gas phase (both sides of the partition)
8
Q
Lambda coefficient is also called ___
A
Ostwald Coefficient/Partition Coefficient
9
Q
Ostwald/partition coefficient refers to potentials of substances in (2 phases)
A
Blood and gas phases
10
Q
The gas phase occurs in the ___
A
Alveoli
11
Q
The blood phase occurs in the ___
A
Arterial/venous blood
12
Q
At equilibrium…. the ___ = ___ = ____
A
Alveoli = arterial blood = brain
13
Q
Partial alveolar is abbreviated as
A
PA
14
Q
Partial arterial pressure is abbreviated as
A
Pa
15
Q
Partial pressure is abbreviated as
A
P
16
Q
Partial brain pressure is abbreviated as
A
Pbr
17
Q
While partial pressures are equal… the anesthetic ___
A
Drug concentration is not equal
18
Q
We determine equilibrium by
A
Input into alveoli - uptake of drug from alveoli into arterial blood
19
Q
Input into alveoli, uptake of drug from alveoli into arterial blood occur during
A
Induction
20
Q
Alveoli are the
A
“Windows to the brain”
21
Q
Leaky bucket concept refers to
A
Drug absorption uptake
22
Q
Drug concentration is (directly/inversely proportional) to partial pressure
A
Directly (but not equal)
23
Q
Increased concentration =
A
Increased partial pressure
24
Q
Decreased concentration =
A
Decreased partial pressure
25
Alveoli are window to the brain... we measure what is in alveoli by
End tidal CO2
26
At equilibrium, alveoli =
Blood partial pressure
27
Diseased lungs require
Increased concentration
28
Transfer from the machine to the alveoli is determined by
Vaporizer and flow meter settings, as well as type of equipment used
29
Never use oxygen <
30%
30
How to flush anesthesia machine for someone concerned with MH (option 1)
100% oxygen at 10L/min for at least 20 minutes
Replace breathing circuit and carbon dioxide canister
Inactivate/remove vaporizers
***newer anesthesia machines may require washout for 104 minutes
31
How to flush anesthesia machine for someone concerned with MH (option 2)
Adding commercially available activated charcoal filters to the circuit will remove anesthetic gases and remove need for purging system
***Anesthesia machine will still need to be flushed with high fresh gas flows >= 10L/min for 90 seconds
32
Higher fresh gas flow & lower absorption =
Faster induction
33
Pediatrics often only use...
Inhalation induction
34
Adults need IV induction as well, then you start inhalation. In theory you have ___
Two inductions
35
IV bypasses
Absorption
36
Inhalation must be ___
Absorbed
37
Alveoli to arterial blood (3 factors)
1. B/Gλ (lipid solubility of agent)
a. Drug you choose/solubility
2. C.O. (pulmonary blood flow)
3. Alveolar to venous partial pressure difference (diffusion gradient)
38
Goal in inhalation induction is to: (3)
1. Decrease gas solubility coefficient
2. Decrease/maintain normal C.O.
3. Increase arterial/venous partial pressure
38
Drug, ventilation and cardiac factors are determined by (2 things) with alveoli to arterial blood
1. Agent chosen
2. Patient's heart and lungs
39
Tissue factors: (3) with arterial blood to brain
1. Brain/blood λ
2. Cerebral blood flow
3. Arterial to venous partial pressure difference (diffusion gradient)
40
Arterial blood to brain tissue factors are determined by 2 things:
1. Agent chosen
2. Patient's heart and lungs
41
Goal of inhalation absorption to tissue: (3)
1. Decreased blood gas solubility coefficient
2. Normal cerebral blood flow
3. Increased arterial/venous partial pressure
42
Barriers that must be overcome to produce an effective anesthetic:
1. Delivered
2. Inspired
3. Alveolar
4. Arterial
5. Tissue
43
MAC stands for
Minimum alveolar concentration
44
MAC compares
Potency of all inhalation agents
45
We breathe in...
78% Nitrogen
21% Oxygen
0.04% CO2 and other mixed gases
46
Pre-oxygenation is reallu
De-nitrogenation
47
At equilibrium, partial pressures are ___ and are reflective of
Equal
Total pressure exerted in alveoli
48
At equilibrium, concentrations are ___, so you must ___
Never equal
Dial the concentrations in
49
Pharmacodynamic effects of inhaled anesthetics must be ___
Based on a dose
50
Pharmacodynamic effects are based on
MAC
51
Each drug has a MAC, each MAC is different, but at that #....
It has equal potency at each MAC
52
Factors that reduce MAC
Increased age
Hypothermia
Admin of sedatives, co-administration of other anesthetics
Alpha 2 agonists
Opioids
Acute ethanol consumption
Hypoxemia
Hyponatremia
Hypermagnesemia
Anemia
Hypotension
Pregnancy
Lithium
53
Factors with no influence on MAC
Duration of anesthesia
Gender
Hypocapnia/hypercapnia
Metabolic alkalosis
Hypertension
Hyperkalemia/hypokalemia
53
Factors that increase MAC
Young age
Hyperthermia
Hyperthyroidism
Hypernatremia
Acute admin of CNS stimulant drugs
Red hair in females
Chronic alcohol abuse
54
1 MAC assesses...
Pt movement (aka ED50)
55
1MAC =
ED50 (no recall, LOC)
56
1.3MAC =
ED95
57
MAC value for N20
105
58
MAC value for Isoflurane
1.15
**1 in elderly
59
MAC value for Desflurane
5.8
**5.17 in elderly
60
MAC value for Sevoflurane
2.0
**1.45 in elderly
61
Pts < 1 year of age...
Have increased MAC
62
MAC decreases what percentage per each decade of life?
6-7% each decade
63
Do you use 105 of N2O?
No, you use 0.6MAC (60%)
64
If MAC is increased, you must give a(n) ____ dose
Increased
65
If MAC is decreased, you must give a(n) ___ dose
Decreased
66
Smaller the dose...
The more potent it is
67
MAC is highest between ____ of age
6-12 months
68
MAC-awake refers to
Approximately 1/3 of MAC
50% will open eyes when asked
69
MAC for loss of recall and awareness are
0.4-0.5 MAC
70
1-MAC
Derived value for agent that assesses movement on incision
71
Surgical-MAC
1.2-1.3x MAC
Anesthetic requirements > MAC by 20-30%
**Surgical MAC is where we operate
72
MAC-BAR
1.6x MAC
**This is where you block adrenergic/stress response
73
What MAC do you block adrenergic/stress response?
MAC-BAR (1.6x MAC)
74
Blood/gas λ of N2O
0.47 (in blood) and 1 in gas
75
Blood/gas λ of Isoflurane
1.4 (in blood) and 1 in gas
76
Blood/gas λ of Desflurane
0.42 (in blood) and 1 in gas
77
Blood/gas λ of Sevoflurane
0.6 (in blood) and 1 in gas
78
Fat/blood λ of N2O
2.3:1
79
Fat/blood λ of Isoflurane
45:1
80
Fat/blood λ of Desflurane
27:1
81
Fat/blood λ of Sevoflurane
48:1
82
What is the preferred inhalation agent in bariatric patients?
Desflurane because fat/blood is lowest true anesthetic of 27
83
FA/FI = 1 = ___
Equilibrium
84
The speed of anesthetic induction (with inhalation) is determined by ___
The rate at which alveolar partial pressure approaches inspired partial pressure
85
FA/FI is
Alveolar: Inspired
85
The key is to look at what is in alveoli (lung) to ___
To determine how fast they will go to sleep
86
FA/FI (interchangeable with FA:FI) is the degree ___
To which alveolar concentration is becoming closer to inspired concentration of anesthetic
86
If alveolar concentration equals the inspired concentration....
The ratio will be 1/1 or 1:1 or simply 1
87
FA/FI = 1 is the same as saying ___
Rate at which alveolar concentration of anesthetic equals inspired concentration of anesthetic
**AKA equilibrium
88
3 factors determining uptake from lung (absorption) alveoli--arterial blood
1. B/G λ solubility of the agent
2. C.O.
3. Alveolar to venous anesthetic partial pressure difference between lung and blood (diffusion gradient)
89
Blood is a pharmacologically ____
Inactive reservoir
90
Blood (inactive reservoir) size is determined by ___
Solubility of anesthetic agent in blood
91
If the B/G λ is high, a ___ amount of anesthetic must be dissolved in blood before the Pa (arterial) equilibrates with alveoli (PA)
LARGE
92
If the B/G λ is low, ___ of the anesthetic must be dissolved in blood before the Pa (arterial) equilibrates with PA (alveoli)
Less
93
An increase in anesthetic uptake (absorption) results in...
A slower induction--- a SLOWING of anesthetic induction (or increase in induction time)
94
The B/G λ (Ostwald) is a distribution ratio describing ___
Itself between two phases: blood and gas
95
Equilibrium is equal to
Partial pressure on both sides
96
B/G λ =
Anesthetic blood concentration/anesthetic alveolar gas concentration
97
Isoflurane's B/G λ is...
1.4
98
With isoflurane:
At equilibrium, the concentration in blood will be ___x the concentration in the alveoli but the partial pressures will be ___
1.4 and equal
1.4:1 or 1.4/1
99
In predicting MAC from O/G λ, what is the formula?
MAC = 150 / (O/G λ)
100
MAC = 150 / (O/G λ is good at determining
Anesthetic potency
100
The correlation between lipid solubility and potency follows which rule?
Meyer-Overton rule
101
What type of oil was used to determine oil/gas solubility?
Olive oil
102
Oil/gas partition coefficient of N20
1.4
103
Oil/gas partition coefficient of Isoflurane
99
104
Oil/gas partition coefficient of Desflurane
18.7
105
Oil/gas partition coefficient of Sevoflurane
50
106
If lipid solubility is increased...
So does anesthetic potency
107
If you know oil/gas...
You can figure out MAC
108
Meyer-Overton rule:
Anesthetic potency of inhalation agents correlates directly with lipid solubility
109
Meyer-Overton rule implies that ___
Anesthesia results from molecules dissolving at specific lipophilic sites
110
Problem with Meyer-Overton rule:
All lipid-soluble molecules are not anesthetic and some are convulsants (correlation between anesthetic potency & lipid solubility is only approximate)
111
O/G λ
How efficiently drug can access the sites of action (potency)
112
B/G λ
How fast drug is delivered to tissue (solubility)
113
Inhalation anesthetics are...
a. potentiaters
b. additive
c. syngergistic
d. antagonists
Additive
114
0.5 MAC of one agent + 0.5 MAC of 2nd agent =
1.0 MAC
115
What gas is the only gas you can add?
Nitrous oxide
116
General rule of thumb using N2O...
1% reduction in MAC for each 1% N2O
117
Uptake (absorption) is ___ proportional to C.O.
Directly
118
Increased C.O. =
Increased uptake (slower induction)A
119
An increased cardiac output means a slower/faster induction
Slower
120
Decreased C.O. = ___ uptake
Decreased uptake (more rapid induction)
121
A decreased cardiac output means a slower/faster induction
Faster
122
Increased C.O. = ___ lung perfusion
Increased
123
Increased lung perfusion =___
Increased drug absorption (increased uptake)
124
Increased drug absorption (uptake) =
Decreased rate of rise in alveolar drug (slower induction)
125
Drug absorption (uptake) is also known as the...
Leaky bucket
126
Decreased C.O. = ___ lung perfusion
Decreased
127
Decreased lung perfusion = ___ drug absorption (uptake)
Decreased
128
Decreased drug absorption (uptake) =
Increased rate of rise in alveolar drug (more rapid induction)
129
The leaky bucket (lung) theory correlates with
Drug absorption
130
The greater the difference in partial pressure between the agent in the alveoli and the ___ the greater the uptake
Will the induction be slower or faster
Venous blood
Slower
131
High pressure in lung is required to get __
Rise
132
If there is no uptake (absorption) of anesthetic gas from alveoli, FA would...
Rapidly equal the concentration of anesthetic gas in inspired gas FI
133
No uptake =
Faster response
134
FA (alveolar) lags behind FI because...
Pulmonary circuit takes up anesthetic gas and lowers concentration in alveoli
135
The greater the amount of uptake (absorption)...
The slower the FA/FI ratio rise toward 1
136
Uptake delays, but it happens to ___ people
ALL
137
Uptake is ____ related to rate of rise of the FA/FI ratio
Inversely
138
There are 3 phenomena influencing uptake & distribution of inhaled agents
1. Concentration (overpressure)
2. Second gas effect
3. Diffusion hypoxia
139
Overpressurization is analogous to...
An upfront IV loading bolus of a drug
140
Overpressurization definition:
The admin of a higher partial pressure of anesthetic than the alveolar concentration actually desired for the patient
141
When you reach equilibrium with overpressurization... what should you do immediately after and why?
Turn gas down because it causes major cardiac depression
142
Concentration effect is d/t: (2)
1. Concentrating effect
2. Hyperventilation effect
143
Concentrating effect definition:
Total volume of lung is decreased by amount of uptake of inhalation agent by the blood (concentrates remaining gas in lung)
144
Hyperventilation Effect/Increased tracheal inflow...
When a large volume of gas is taken up by the blood a negative pressure is created and fresh gas inflow augments alveolar ventilation
145
Concentration effect's biggest difference occurs in how many breaths?
2-3
146
Concentration effect speeds up induction by the concentrating effect and the ___
Hyperventilation effect
147
Net effect means
You are delivering a greater concentration of agent than is actually being administered
148
Second gas effect is the uptake of large volumes of a ___
1st primary gas (N2O) that accelerates alveolar rate of rise of a 2nd gas (isoflurane) administered at the same time
149
Second gas effect theory:
Rapid uptake of primary gas concentrates the second gas because of the decrease in total lung volume
150
To tell the difference between concentration vs. second gas... ask yourself...
Are you giving 1 or 2 gases?
151
Concentration and second gas effects do what to induction and emergence?
Hasten (speed up)
152
Concentration and second gas occur during ___ for approximately ___
InductionF
First 5-15 minutes (most dramatic and significant within first few breaths)
***Occurs during emergence for first 5 min
153
Diffusion hypoxia (anoxia) occurs during what phase... induction, maintenance, or emergence?
Emergence
154
Diffusion hypoxia ONLY occurs with the use of ___
N2O
**Postop first 5 min
155
To avoid diffusion hypoxia you should....
Wake the patient up with oxygen
156
Why does diffusion hypoxia occur?
Nitrogen comes in/out and crowds the lungs and causes hypoxia
157
SHUNTS:
Examples of right-to-left shunt (2)
Intra-cardiac shunt
Intra-pulmonary shunt (bronchial intubation)
158
SHUNTS:
Example of left-to-right shunt (1)
Tissue shunt
159
Which type of shunt can cause de-oxygenation?
Right-to-left (they are cyanotic)
160
Examples of tissue shunts (not significant in de-oxygenation)
AV fistula
Volatile anesthetic induced in increase in cutaneous blood flow)
161
Right-to-left shunts could slow the rate of induction d/t a ____
Dilutional effect
162
Right-to-left shunts have greater impact on:
poorly soluble agents like:
Desflurane
Sevoflurane
N2O
163
Right-to-left shunt compensation for deficits: (2)
Increased concentration of insoluble agents
Increased ventilation w/ soluble agents
164
Right-to-left shunt = decreased or increased PA
Decreased
165
Left-to-right shunts result in delivery to ___
Lungs of venous blood with a higher partial pressure of anesthetic than that present in blood (that has passed through tissue)
166
Left-to-right shunts increase or decrease PA tension
Increase
167
Is a left-to-right shunt alone detectable?
No
168
What type of shunt is detectable?
Right-to-left
169
In the presence of a right-to-left shunt, a left-to-right shunt will ____
Offset dilution effects (could prolong IV induction)
170
Three stages of anesthesia:
Induction
Maintenance
Recovery
171
Induction has three:
Excitement (see in children mostly)
Rigidity (set their jaw)
Relaxation
172
Maintenance has two:
Constant (set anesthesia machine)
Variable (we adjust w/ variable)
173
Recovery has two:
Crisis (very rapid wake up)
Lysis (smooth even w/ wake up)
174
We want patients in the ____ phase of recovery
Lysis
175
What gas is preferred in bariatric?
Desflurane
176
Three factor equation for uptake from lung:
UL = λB Q(PA - PV) / BP
