The inhaled anesthetic agents & physiological effects Flashcards
1
Q
What IA is rate of emergence most rapid?
A
with the least soluble inhaled anesthetics (nitrous oxide, desflurane, sevoflurane)
2
Q
What happens when inhaled anesthetic administration is abruptly stopped?
A
skeletal muscle & fat don’t initially release the anesthetic back into the bloodstream for degradation in the liver
3
Q
More soluble inhaled agents = ___________ emergence
A
slower/longer
4
Q
What does elimination of inhaled anesthetics depend on?
A
Length of administration,
Blood-gas solubility of the inhaled anesthetic
5
Q
What is important with inhaled anesthetics for long period of time ?
A
Context-sensitive half time important with administration
6
Q
What is floods example of context sensitive half time?
A
If an anesthetic is 3-4 hrs duration, then about 30 min before the end of the case, turn off sevoflurane and replace it with 70% N2O
(This gives sevoflurane adequate time to decrease 90% & rapid recovery once N2O is DCd at end of surgery)
7
Q
Review context sensitive half time.
A
Slide 47
8
Q
What effect does the greater the uptake of the anesthetic have? (3)
A
the greater the difference between inspired and alveolar concentrations, and the slower the rate of induction.
9
Q
What effect does low-output states have?
A
predispose patients to overdosage with soluble agents, as the rate of rise in alveolar concentrations will be markedly increased.
10
Q
What are some key factors that speed induction & recovery? (6)
A
- Elimination of rebreathing, high fresh gas flows
- Low anesthetic-circuit volume
- Low absorption by the anesthetic circuit
- Decreased solubility
- High cerebral blood flow
- Increased ventilation
11
Q
What is the Blood: Gas Partition Coefficient of methoxyflurane?
A
12
12
Q
What is the Blood: Gas Partition Coefficient of halothane?
A
2.54
13
Q
What is the Blood: Gas Partition Coefficient of enflurane?
A
1.90
14
Q
What is the Blood: Gas Partition Coefficient of isoflurane?
A
1.46
15
Q
What is the Blood: Gas Partition Coefficient of Nitrous oxide?
A
0.46
16
Q
What is the Blood: Gas Partition Coefficient of Desflurane?
A
0.42
17
Q
What is the Blood: Gas Partition Coefficient of Sevoflurane?
A
0.69
18
Q
What is the Blood: Gas Partition Coefficient of Xenon?
A
0.115
19
Q
What are intermediately soluble agents?
A
Halothane, Enflurane & Isoflurane
20
Q
What are intermediately poor soluble agents?
A
Nitrous oxide, desflurane, sevoflurane and xenon
21
Q
What is the smell properties of nitrous oxide?
A
Odorless, sweet smelling
22
Q
What is true about the solubility of nitrous oxide?
A
poor blood solubility that results in rapid alveolar and brain partial pressures
23
Q
Nitrous OXIDE: Mostly used in _________ with other agents (except dental)
A
Conjunction
24
Q
What is the flammability of nitrous oxide?
A
Not flammable but is an oxidizing agent that WILL SUPPORT COMBUSTION
25
What is true about the storage of nitrous oxide?
Only “nonvolatile” inhaled anesthetic, an inorganic gas in gas state at room temp (liquified under pressure and stored in blue tanks)
26
What is the principle characteristic of nitrous oxide?
Rapidly expands closed air spaces (readily crosses lipid membranes diffuses 35 times faster into closed air spaces than nitrogen can diffuse out)
27
When is nitrous oxide contraindicated? (8)
venous or arterial air embolism, pneumothorax, acute intestinal obstruction w/bowel distension, intracranial air/pneumocephalus, pulmonary air cysts, intraocular air bubbles, tympanic membrane grafting
28
What is true about nitrous oxide and tracheal cuffs?
Will also diffuse into tracheal tube cuffs increasing the pressure against the tracheal mucosa
29
What is the MOA of nitrous oxide?
NMDA receptor antagonist
30
What is the elimination and uptake of nitrous oxide?
Rapid
31
What is the effects on skeletal muscles with nitrous oxide? What can it cause at high concentrations?
Minimal skeletal muscle relaxation & Causes skeletal muscle rigidity at high concentrations
32
What are the cardiac physiology of nitrous oxide? Why do you not see these?
Myocardial depressant, it has Mild sympathomimetic
33
What does nitrous oxide have on MAC?
Reduces MAC of potent volatile inhaled anesthetics
34
What is the respiratory effects of nitrous oxide?
Pulmonary vascular smooth muscle constriction/ increases pulmonary vascular resistance
35
What CNS effect occurs from Nitrous oxide?
Increases CBF, CBV, & CMRO2
36
What is true about analgesia and nitrous oxide?
Concentrations below MAC may provide analgesia (dental surg, labor, minor surg procedures) – analgesia ends once N2O admin. ceases
37
How does nitrous oxide increase the risk of PONV?
Increases risk of PONV d/t activation of the chemoreceptor trigger zone & vomiting center in medulla
38
What does nitrous oxide inactivate by the oxidation of cobalt?
vitamin B12 (methionine & thymidylate synthetase enzyme)
39
What is the importance of methionine synthetase?
converts homocysteine to methionine which is crucial in DNA, RNA, myelin, catecholamines.
40
What can a decrease of methionine result in?
in both genetic and protein abnormalities (concerns with repeated exposures within 3 days)
41
What changes occur from the inactivation of B12 by nitrous oxide?
Megaloblastic changes in bone marrow & Peripheral neuropathy
42
Who is most vulnerable for the inactivation of vitamin b12 by nitrous oxide?
Extremes in age are most vulnerable
43
What occurs when nitrous oxide is abruptly stopped?
Diffusion Hypoxia
44
What occurs with diffusion hypoxia?
discontinued which leads to reversal of partial pressure gradients such that nitrous oxide leaves the blood to enter the alveoli
45
Describe the relationship of diffusion hypoxia and nitrous oxide?
- PAO2 is diluted with N2O so that PaO2 decreases
- Also dilution of the PACO2 = decreases the stimulus to breath
46
When is diffusion hypoxia from nitrous oxide is of greatest concern?
Of greatest concern during the first 1-5 minutes after its discontinuation of nitrous oxide
47
What is the treatment of NO diffusion hypoxia?
Increase oxygen flows at end of the anesthetic once nitrous oxide is discontinued
48
What is the chemical property of halothane?
Halogenated alkane
49
What is true about the use of halothane in the US?
Not used in the US any longer
50
What is halothane susceptible to decomposition to?
Susceptible decomposition to HCl & hydrobromic acid (used thymol preservative)
51
What agent is associated with used thymol perservative?
Halothane
52
What is the smell properties of halothane?
Sweet and nonpungent
53
What is halothane most commonly used with? What has it been replaced with?
Used with pediatric inhalational inductions along with nitrous (replaced with Sevoflurane)
54
What is true about the induction of halothane?
Unlike SEV- had to slowly increase concentration delivered to induce: could not do a 1-2 breath induction
55
What are the cardiac effects of halothane? (2)
Direct myocardial depression & slowing of sinoatrial node conduction
56
What are two arthymias associated with halothane?
May result in junctional rhythm & bradycardia
57
Halothane is associated with Dose-dependent ________ in cardiac output
decrease
58
What effect does halothane have with epinephrine?
Sensitizes heart to arrhythmogenic effects of epinephrine
59
What effect does halothane have on blood flow in the CNS?
Lowers cerebral vascular resistance, increase CBF, blunts autoregulation
60
What effect does halothane have on hypoxic drive? What cellular effect can be seen?
Hypoxic drive depressed (decrease alveolar ventilation, increase resting Paco2)
61
What is the respiratory effects of halothane?
Potent bronchodilator by inhibiting intracellular Ca++ influx
62
What hepatic effect can be see by halothane?
decreased hepatic blood flow
63
Describe the variation in metabolism by the CYP450 of halothane, desflurane, sevoflurane and isoflurane.
Metabolism: HAL (20%) \> SEV (5%) \> ISO (2%) \> DES (0.02): All by CYP450 system
64
What does metabolism of halothane result in?
oxidative process that results in trifluoroacetyl halide and an immune response
65
What are two important liver effects of halothane?
Hepatotoxicity & Halothane hepatitis
66
What side effect is most implicated with halothane?
Hepatotoxicity, but can involve any of the volatile agents
67
What predisposes someone to hepatotoxicity by halothane?
Predisposition with liver disease will increase likelihood
68
What is the physiological pathology hepatotoxicity by halothane?
Inadequate hepatocyte oxygenation due to ↓ alveolar ventilation (hepatic hypoxia) or ↓ hepatic blood flow
69
What can increase the risk of heptatotoxicity?
Enzyme induction (i.e., with phenobarbital) lead to production of hepatotoxic end products of metabolism & increased risk of hepatotoxicity
70
What are the characteristics of halothane hepatitis?
- extremely rare, 1:30,000, results from changes in hepatic blood flow
- Resembles acute hepatitis
- Antigen-antibody interaction (immunoglobulin G)
71
What is the risk factors of halothane hepatitis? (3)
female, middle age, obesity, prior exposure to halothane
72
What are the symptoms associated with halothane hepatitis?
fever, rash, arthralgia, eosinophilia
73
What is another inhaled anesthetic no longer used in anesthesia?
Enflurane, No longer used in the US
74
What effect does enflurane have on seizures?
Decreased the threshold for seizures
75
How is enflurane oxidized?
Oxidized in the liver to inorganic nephrotoxic fluoride (physiological effects)
76
What activity is enflurane tide to?
Tied to EEG seizure activity
77
What is the chemical storage of isoflurane?
Clear, nonflammable liquid at room temp (isomer to enflurane)
78
What is the solubility of isoflurane?
Intermediate solubility (more soluble than sevoflurane and desflurane so induction and emergence are slower)
79
What is the smelling properties of isoflurane? What does this mean for induction?
Pungent odor/airway irritant – poor choice for inhalation induction
80
What is isoflurane is characterized by?
Characterized by extreme physical stability (no deterioration with prolonged storage, does not interact with CO2 absorber or sunlight)
81
What is the cost of isoflurane?
Cheap
82
What is the cardiac effect of isoflurane?
Minimal LV depression
83
What can be cause by rapid increases in concentration of isoflurane?
Rapid increase in concentration may lead to transient incr. in HR & BP
84
What respiratory effect can be seen with isoflurane?
- Decrease in alveolar ventilation causes rise in resting Paco2 & depresses ventilatory response to increase Paco2
- bronchodilation
85
What CNS effects can be see with Isoflurane?
- Increases CBF and ICP at \> 1MAC (reversed by hyperventilation)
- Reduces CMRO2
86
What is the CNS protective effects of isoflurane?
May offer degree of cerebral protection
87
What is isoflurane metabolized too?
Metabolized to trifluoroacetic acid – may cause rise in serum fluoride levels
88
What is rare with isoflurane?
nephrotoxicity rare
89
What are the chemical properties of desflurane?
Fluorination rather than chlorination increases its vapor pressure, enhances stability, decreases potency
90
Which inhaled anesthetic has the highest vapor pressure?
Desflurane (Suprane) (660 mmHg at 20 degrees C)
91
What is the storage of desflurane?
Liquid would boil at room temperature
92
What is required by desflurane do to its high vapor pressure?
Requires a special electrical vaporizer that is heated and pressurized (39 degrees C at 2 atm)
93
What is true about desflurane's blood:gas solubility?
Its lower blood:gas solubility (0.42) allows for rapid onset/offset
94
What is the smell properties of desflurane?
Is very pungent & an airway irritant
95
Why are the characteristics that make desflurane a poor choice for inhalation induction?
airway irritant (breath holding, coughing, laryngospasm, can increase airway resistance in patients w/ reactive airways
96
What can desflurane cause in smokers?
bronchoconstriction
97
What is the respiratory effects of desflurane?
Decrease in alveolar ventilation causes rise in resting Paco2 & depresses ventilatory response to increase Paco2
98
What can rapid increases in concentration in desflurane? Who is this contraindicated in?
Rapid increases in concentration lead to transient elevation in HR, BP, & catecholamine levels can last several minutes (undesirable in patients with CAD)
99
What can increase in HR/BP can be seen by Increasing DES concentration from 4% to 8% over \< 1 min?
incr. HR/BP up to 2x baseline
100
What are the potential cause of the increased HR/BP effects of desflurane?
rapidly adapting airway receptors, renin-angiotensin system activation, or central adrenergic stimulation
101
What can attenuate the cardiac effects of desflurane?
response w/ fentanyl, esmolol, or clonidine
102
What CNS effect can be seen with desflurane?
Increases CBF, CBV, & ICP / decreases CMRO2
103
What can desflurane produce? How?
CO production with desiccated CO2 absorber/interaction with strong base in CO2 absorer - Desflurane the greatest for CO production:
104
What does CO production of desflurane cause?
carboxyhemoglobin
105
What are potential causes of CO production from desflurane?
- High fresh gas flows through AGM left on high when not in use
- High temperature of CO2 absorber from low gas flows & long case
- Type of CO2 absorbent
106
What are the two types of CO2 absorbents that can interact with Desflurane?
sodium & potassium hydroxide, barium hydroxide soda lime
107
What is another side effect associated with Desflurane?
CO poisoning: difficult to dx under general anesthesia
108
What are the signs associated with CO poisoning?
- Carboxyhemoglobin level: ABG
- Lower than expected pulse oximetry readings (but still falsely high)
109
What is important to note about desflurane and the AGM?
turn off fresh gas flows on the AGM between cases and at the end of the day (consider turning AGM off at end of day unless OR is on standby for an emergency case)
110
What is sevoflurane halogenated with?
Halogenated w/fluorine (desflurane is too)
111
What is the blood:gas solubility of sevoflurane? What does this allow?
Blood:gas solubility (0.69) slightly higher than desflurane (allows fast onset/offset)
112
What is the smell of sevoflurane?
Nonpungent
113
What is the preferred agent for inhalational inductions for adults and children?
Sevoflurane
114
What do the properties of sevoflurane allow for?
able to deliver a high concentration from the onset to increase PA (“turn up the dial”); induction is smooth & rapid
115
What is the characteristics of inhalation induction with 4%-8% sevoflurane?
in a 50% mixture of nitrous oxide and oxygen can be achieved within 1 min.
116
What is the respiratory effects of Sevoflurane?
Decreases CO2 drive, Bronchodilation
117
Sevoflurane is least likely to \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_.
react with CO2 absorber to form CO
118
What can occur with sevoflurane at a MAC of 1.5-2?
Apnea
119
What are some isolated incidents that have occurred between sevoflurane and AGMs?
Isolated incidents of fire in the respiratory circuits of AGMs w/desiccated CO2 absorbents (\*\*\*turn off fresh gas flows in-between cases and at end of the day!)
120
What does sevoflurane react with? What does this produce?
Reacts with bases in barium hydroxide lime or soda lime CO2 absorbers (containing barium, sodium, or potassium hydroxide) to form Compound A (a vinyl ether
121
What is Compound A toxic too?
Renal toxic
122
What increases the risk of compound A? (5)
Risk increases with increased respiratory gas temperature, low-flow anesthesia, dry barium hydroxide absorbent (Baralyme), high sevo concentrations, & anesthetics of long duration
123
What was discontinued in 2004 because of compound A and sevoflurane?
Barium hydroxide absorbers
124
When is gas flows not an issue for compound A production?
Not an issue with gas flows of at least 2 lpm which reduces accumulation
125
Absorbers containing ________ do not degrade sevoflurane.
calcium hydroxide
126
\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ do not degrade sevoflurane
Newer CO2 absorbers (i.e., lithium)
127
What is sevoflurane metabolism more vulnerable to?
to inorganic fluorides – no association with peak fluoride levels following sevoflurane and any clinically significant renal dysfunction
128
What is xenon?
Noble gas/inert element
129
What is the characteristics of xenon?
Nonexplosive, nonpugnent, odorless, no metabolism, low toxicity
130
Why is Xenon not used as often?
Expensive (must be purified from the atmosphere). #54 on periodic table
131
What is the MOA of Xenon?
Anesthetic effects mediated by NMDA inhibition by competing w/glycine at glycine binding site
132
What is the MAC of Xenon?
MAC 0.71
133
What is the blood: gas solubility of Xenon?
Lowest blood:gas solubility (0.115)
134
What is the nitrous oxide effect on MH?
Not a triggering agent of MH
135
What is the evoke effects of inhaled anesthetics?
inhaled anesthetics produce dose-dependent decrease in amplitude & increased latency in evoked potential monitoring (somatosensory, motor, brainstem, auditory, and visual)
136
What are some surgeries that monitor evoke potentials?
spinal cord/neuro surgeries & neurophysiologic monitoring
137
Visual-evoked potentials \_\_\_\_\_\_\_\_\_
Most sensitive
138
Brainstem-evoked potentials \_\_\_\_\_\_\_\_\_
most resistant
139
What are the general CNS effects of inhaled anesthetics? (4)?
Produce cerebral vasodilation, decreased cerebral vascular resistance, increased CBF, decreased CMRO2
140
What inhaled anesthetic has the most myocardial depression?
Halothane
141
What inhaled anesthetics decrease SVR?
isoflurane, desflurane, sevoflurane
142
What Cardiac effect is most common with inhaled anesthetics?
Decreased MAP: isoflurane, desflurane, & sevoflurane via decreased SVR; halothane via decreased cardiac output
143
What causes ventilatory depression and decreased PaO2?
depression of medullary ventilatory centers - occurring with spontaneous vent; this effect offset with mechanical/controlled ventilation
144
What ventilatory response can be seen with inhaled anesthetics?
Depressed ventilatory response to hypoxemia (normally mediated by carotid bodies) & hypercarbia
145
What tidal volume response can be seen with inhaled anesthetics?
Decreased tidal volume with spontaneous ventilation: rapid & shallow pattern of breathing
146
What temperature effect can be seen with inhaled anesthetics?
Increased cutaneous blood flow results in loss of body heat (central inhibition of temperature regulation)
147
What is true regarding inhaled anesthetics besides nitrous oxide?
All inhaled anesthetics (except nitrous oxide) are triggers for malignant hyperthermia
148
What is the receptor associated with malignant hyperthermia?
ryanodine receptor [RYR1] plays important role in Ca ++ release from sarcoplasmic reticulum)
149
Inhaled anesthetics potentiate \_\_\_\_\_\_\_\_
nondepolarizing NMBDs
150
What are possible effects of inhaled anesthetics?
Possible neuro and cardiac protection (iso, sevo, & des)
151
What is true about inhaled anesthetics and skeletal muscle relaxation?
Incompletely inhibit skeletal muscle nicotinic receptors leads to skeletal muscle relaxation (incomplete)
