Inhalation Agents II Flashcards
1
Q
Nitrous oxide molecular formula
A
N2O
2
Q
Nitrous oxide blood:gas coefficient
A
0.46
3
Q
Nitrous oxide oil:gas partition coefficient
A
1.4
4
Q
Nitrous oxide vapor pressure
A
38,700
Gas
5
Q
Nitrous oxide boiling point
A
-88 C
6
Q
Nitrous oxide molecular weight
A
44
7
Q
Nitrous oxide MAC
A
104
8
Q
Isoflurane molecular formula
A
C3H2CIF5O
9
Q
Isoflurane blood:gas coefficient
A
1.46
10
Q
Isoflurane oil:gas coefficient
A
91
11
Q
Isoflurane vapor pressure
A
238
12
Q
Isoflurane boiling point
A
49 C
13
Q
Isoflurane molecular weight
A
184
14
Q
Isoflurane MAC
A
1.17
15
Q
Desflurane molecular formula
A
C3H2F6O
16
Q
Desflurane blood:gas partition coefficeint
A
0.42
17
Q
Desflurane oil:gas partition coefficient
A
19
18
Q
Desflurane vapor pressure
A
669
19
Q
Desflurane boiling point
A
24 C
20
Q
Desflurane molecular weight
A
168
21
Q
Desflurane MAC
A
6
22
Q
Sevoflurane molecular formula
A
C4H3F7O
23
Q
Sevoflurane blood:gas partition coefficient
A
0.65
24
Q
Sevoflurane oil:gas partition coefficient
A
47
25
Sevoflurane vapor pressure
157
26
Sevoflurane boiling point
59 C
27
Sevoflurane molecular weight
200
28
Sevoflurane MAC
2
29
Halothane molecular formula
C2HBrClF3
30
Halothane MAC
0.75
31
Halothane blood:gas partition coefficient
2.54
32
Halothane oil:gas partition coefficient
224
33
Halothane vapor pressure
244
34
Halothane boiling point
50.2 C
35
Halothane molecular weight
197
36
Xenon MAC
71
37
Xenon blood:gas partition coefficient
0.115
38
Xenon oil:gas partition coefficient
1.9
39
Xenon boiling point
-108 C
40
FI-Factors affecting inspiratory concentration
Fresh gas flow
Breathing system volume
Machine absorption
41
FA-Factors affecting alveolar concentration
Blood solubility of the agent
Alveolar blood flow
Partial pressure between alveoli and venous blood
42
Fa-Factors affecting arterial concentration
Alveolar and arterial anesthetic partial pressures are considered equal
Fa is less than end-tidal level would predict
-Venous admixture
-Alveolar dead space
-Non-uniform distribution
43
What anesthetic gas is metabolized the most?
Sevoflurane
| 5-8%
44
What are factors that effect the absorption of anesthetic gases?
Temperature
Solubility
Ventilation
Cardiac output
45
What are factors that effect the distribution of gases?
Lipid solubility
Tissue related factors
Metabolism
46
Where in the CNS does amnesia occur?
Brainstem
47
Where in the CNS does analgesia occur?
Thalamic tract
48
Where in the CNS does areflexia occur?
Spinal cord
49
Which solubility coefficient is the indicator of the speed of uptake and the elimination of the drug?
Blood:gas coefficient
50
Which solubility coefficient determines how efficiently the anesthetic gas is going to move through the blood to the tissues to the target?
Oil:gas coefficient
51
What is unique about Desflurane?
Low blood:gas solubility
52
What is unique about Isoflurane?
Potent
| High oil:gas solubility
53
What do you do if you want to get your gas on more quickly?
Increase flow
54
What can you do to increase rate of rise of FA/Fi?
```
Increase concentration (over pressure)
Second gas effect
Increase minute ventilation*
Decrease CO*
Decrease solubility*
```
55
Where do anesthetic gases go first?
Vessel rich group
| Includes brain
56
What percentage of cardiac output goes to the vessel rich group?
75%
57
What percentage of cardiac output goes to the muscle?
19%
58
What percentage of cardiac output goes to fat?
6%
59
What would expect if ETT only goes into right mainstem?
Right side of lung is being ventilated and perfused.
Left side of the lung is being perfused.
VQ mismatch
60
Ventilation/perfusion mismatch
Right bronchial intubation or PFO
Overall effect is increase in alveolar partial pressure (highly soluble agents like isoflurane) and decrease in arterial partial pressure (low solubility agents)
61
Most likely targets of anesthetic gases
```
NMDA receptors
Tandem pore K+ channels
VG NA+ channels
Glycine receptors
GABA receptors
```
62
Meyer Overton theory
Also called critical volume hypothesis
Lipophilicity equates potency (increasing oil:gas coefficient)
Says that if you administer a large volume of anesthetic gas, eventually will hit critical volume threshold where the drugs will cross lipid bilayer
Says effect some ion channels but does not specify
63
How do anesthetic gases effect CMRO2
Decreased
64
How do anesthetic gases effect cerebral blood flow?
Cerebral blood flow (CBF) increased (dose-dependent)
Increases ICP
65
What phenomenon describes the increase of CBF?
Which anesthetic gas causes this the most?
Uncoupling
Sevoflurane
66
How does nitrous gas effect CMRO2 and CBF?
Increases CMRO2
| Increases CBF
67
How do you decrease ICP?
Mild hyperventilation
| 30-35 mmHg
68
How do anesthetic gases effect evoked potentials?
Decrease amplitude and increase latency
69
What is burst suppression?
Term used to describe an EEG pattern associated with high-voltage, mixed frequency, slow wave activity, along with periods of electrical suppression that lasts several seconds.
70
Burst suppression occurs at:
1.5 MAC of Desflurane
| 2 MAC with Isoflurane and sevoflurane
71
What type of anesthetic would you use if you are doing any neuromonitoring case?
TIVA
72
Postoperative cognitive dysfunction
Greater concern in the elderly
| No clinically significant association between major surgery and anesthesia with long-term POCD
73
Emergence delirium in children
More common with sevoflurane and desflurane
74
How do inhalation agents effect cardiac output?
Reduce cardiac output and index in dose-dependent fashion
75
What happens to CI and HR as MAC hours increase?
Slight increase
76
Inhalation agents effect on MAP
Reduced MAP secondary to SVR reduction
Nitrous oxide used in combination with anesthetics reduces this
77
Heart rate decreases with
Halothane
78
Heart rate increases with
Isoflurane
Desflurane (tachycardia)
Sevoflurane
79
Volatile agents and nitrous oxide induce HR changes via
Unknown exactly, could be:
SA node antagonism
Modulation of baroreflex activity
SNS activity
80
All inhalation agents produce some vasodilation
True
Decrease SVR, leads to decrease in MAP
EXCEPT for nitrous oxide
81
Reverse Robin Hood or Coronary Steal
Seen the most with isoflurane
Response to hypotension
If body is having ischemic area in cardiac tissues, body will shunt blood away from those tissues.
Perfuses good tissue, not perfusing ischemic areas.
82
What is preconditioning?
A phenomenon in which the heart is exposed to a cascade of intracellular events that protect it from ischemic and reperfusion insult
83
What is sensitization?
Volatile agents reduce the quantity of catecholamines necessary to evoke arrhythmias
84
How is PVR effected by nitrous oxide?
Slight increase
Other volatile agents have no effect
Worsens in pts with pulmonary HTN
85
How do volatile agents effect pulmonary artery pressure?
Decrease
86
Hypoxic pulmonary vasoconstriction
Mildly depressed
Isoflurane has the greatest effect
Normal physiologic response of body to vasoconstrict areas that are not being oxygenating, this response is depressed.
87
Respiratory effects of inhalation agents
Decrease in tidal volume: compensated by increase in RR (but not sufficient to offset TV)
Responsiveness to hypoxemia
Responsiveness to CO2
-increases apneic threshold
-exacerbated by co administration of opioid
Relax airway muscle and produce bronchodilation
88
Airway irritant
Desflurane
| Don't use for induction
89
What happens to the CO2 response curve?
Shifts to the right
| Decrease response to CO2
90
Effect of inhalation agents on GFR and UO
Decreases
91
Which inhalation agent effects renal function the least?
Desflurane
92
Which inhalation agent effects renal function the most?
Sevoflurane because of degradation that leads to increase of fluorine ions that can cause renal injury
To counter this: should not exceed 2 MAC hours at flows <2L/min
93
Halothane hepatitis
Why we don't use it anymore
Most likely caused by trifluoracetyl-containing metabolites binding to proteins and
forming anti-trifluoroacetyl protein antibodies
Re-exposure of the patient to halothane these antibodies mediate massive
hepatic necrosis that can result in death
94
THE IDEAL ANESTHETIC AGENT
- Non-irritating to the respiratory tract
- Rapid induction and emergence
- Chemically stable (non-flammable)
- Produce amnesia, analgesia and areflexia
- Potent
- Not metabolized and excreted by respiratory tract**
- Free of toxicity and allergic reactions
- Minimal systemic changes
- Uses a standardized vaporizer
- Affordable
95
Neuromuscular effects
All volatile agents produce a dose-dependent relaxation on
skeletal muscle
• Additive effect on non-depolarizing NMBDs
• Can be reduced 25-50% of dose when compared to TIVA
• Delay recovery from non-depolarizing NMBDs
96
Vapor pressure
Pressure exerted inside a container between liquid and vapor
At room temperature most volatile agents have a vapor pressure below atmospheric
pressure
As long as liquid is present, vapor pressure is independent of volume
Directly proportional with temperature
97
Boiling point
Temperature at which vapor pressure exceeds atmospheric pressure in an open
container
98
Partial pressure
Fraction of pressure within a mixture (Dalton’s Law)
99
Solubility
Tendency of a gas to equilibrate with a solution (Henry’s Law)
• Anesthetic gases administered to the lungs diffuse into the blood until the partial
pressures of the alveoli and blood are equal
• Equalizing of blood and target tissues occurs similarly; however there is no gas phase
100
MAC
The definition of MAC is the minimum alveolar concentration
(%) required to produce anesthesia (lack of movement) in
50% of the population (ED50)
101
MAC ‘awake’
the MAC in which 50% of the population opens eyes to command
102
MAC 'BAR'
MAC ‘BAR’ – the MAC necessary to block adrenergic response to
stimulation
Usually 1.3 of MAC value
Can be reduced by administering a narcotic prior to incision
103
What happens to MAC with age?
Decreases with age
• 6% decline each decade after the age of 40
• MAC relatively unaffected by gender, duration of anesthesia,
comorbidities
• Red-haired females?
104
Additive effect
• 0.5 MAC of nitrous oxide + 0.5 MAC of isoflurane = 1 MAC sevoflurane
105
Factors that increase MAC
* Hyperthermia
* Drug-induced increases in CNS activity
* Hypernatremia
* Chronic alcohol abuse
106
Factors that decrease MAC
* Hypothermia
* Increasing age*
* Alpha -2 agonists
* Acute alcohol ingestion
* Pregnancy
* Hyponatremia
107
Isoflurane
Halogenated methyl ethyl ether
• Most potent of the current volatile agents**
• Slower onset and recovery from anesthesia
Cardiovascular
• Minimal cardiac depression; preserves carotid baroreceptors
• Dilates coronary arteries; concern for ‘reverse-Robin Hood’
Respiratory
• Pungent; not used for inhalational induction
• Tachypnea less pronounced
108
Vaporizers
The delivery device for volatile agents
• Facilitate the movement of anesthetic from the machine to the patient
through
• Fresh gas flow
• Pressure
• Temperature
• Vaporizers are calibrated for specific agents
109
Desflurane
Least potent of the volatile agents
• Quicker induction and emergence
• Potential to boil at room temperature
Cardiovascular
• Rapid increases in desflurane lead to increases
in HR and BP
• Attenuated with fentanyl, esmolol, clonidine
Respiratory
• VERY pungent; can cause airway irritation,
increased salivation, breath holding, coughing,
laryngospasm
• Avoid in patients with reactive airway disease
110
Sevoflurane
Fluorinated methyl isopropyl ether
Moderate potency
• Rapid induction and emergence
Cardiovascular
• May prolong QT interval; clinical significance?
• Cardiac output is less maintained than other volatile agents
• HR not increased
Respiratory
• Non-pungent; preferred volatile for inhalational induction
111
Sevoflurane Metabolism
* CYP-450 2E1 metabolizes 5-8% of sevoflurane
* Increase in inorganic fluoride(F-) ions
* However, never shown to result in nephrotoxicity
112
Sevoflurane renal effects
Soda lime can degrade sevoflurane into Compound A:
Increased gas temperature, low flow anesthesia, high sevoflurane concentrations
and prolonged surgeries
Nephrotoxic in rats, not humans
For safety: Calcium hydroxide absorbent, flows 2 lpm, avoid in patients with renal dysfunction
113
Nitrous oxide
Not a volatile anesthetic; colorless and odorless
• Gas at room temperature
• Kept as a liquid under pressure (745 psi)
• Nonexplosive and nonflammable
• However, it does support combustion like oxygen
• NMDA receptor antagonist
• May lower risk chronic pain after surgery
114
Nitrous oxide decreasing in popularity?
Chronic exposure can lead to inactivation of vitamin B12 cofactor for enzyme synthesis, disrupting DNA synthesis leading to teratogenic, bone marrow and immunosuppression effects
115
Nitrous oxide CV
* Stimulates sympathetic nervous system
| * BP, HR, CO unchanged or slightly elevated
116
Nitrous oxide respiratory
* Increases respiratory rate
| * Decreases hypoxic drive
117
Nitrous oxide cerebral
• Increases CMRO2 and CBF
| Don't use for gas filled spaces because N2O is 34 times more soluble than nitrogen (ENT, bowel cases)
118
Nitrous oxide GI
• Increases the risk of PONV
119
Nitrous oxide absolute contraindications
Methionine synthase pathway deficiency
| • Expansion of gas-filled space
120
Nitrous oxide relative contraindications
* PONV
* First trimester of pregnancy
* Increased ICP
* Pulmonary hypertension
* Prolonged surgery (> 6 h)
121
Xenon
Noble gas with known anesthetic properties
• Odorless, colorless, non-explosive naturally occurring
• Inert, does not form chemical bonds
Actions via NMDA and glycine receptor binding sites
Minimal cardiovascular, hepatic or renal effects
• Neuroprotective?
No effect on the ozone layer
Cost and limited availability have prevented widespread use
Favors air bubble expansion
122
Malignant hyperthermia is triggered by
```
• Volatile anesthetics
-nitrous oxide is considered acceptable
• Succinylcholine
• Stress
Ryanodine receptor gene mutation (chromosome 19)
```
123
MH signs and symptoms
* Increase in carbon dioxide production
* Muscle rigidity
* Metabolic acidosis
* High temperature (late sign)
* Muscle rigidity
* Increase in ETCO2
* Increase in body temperature
* Urine color darkens
* Tachycardia
* Tachypnea
124
MH treatment
```
• Dantrolene sodium – muscle relaxant
• 1mg/kg (supplied in 70 mL vials containing 20 mg of Dantrolene, 3000 mg of
Mannitol and sodium hydroxide)
• Administer until symptoms subside
• Up to 10 mg/kg
```
Ryanodex
• New IV formulation of dantrolene for the prevention and treatment of MH
• Requires fewer dials and less reconstitution
• Shorter half-life
• Requires supplementation of mannitol
125
Halothane CV
More likely to induce arrhythmias
Alkyl halide
Susceptible to degradation, stored in amber bottles
126
Pregnancy
Between 0.2-0.75% of pregnant patients may require general
anesthesia
• Most common appendectomy, cholecystectomy, ovarian or trauma
Some clinicians avoid nitrous oxide due to teratogenic effects
• Elective surgery should be delayed until after delivery
• Non-urgent surgery should be performed in the second trimester
127
Obesity causes
Delayed emergence
128
Measure depth of anesthesia
Pbrain
129
Does nitrous oxide cause skeletal muscle relaxation?
No
