Ch 16 - Anesthetics - DONE Flashcards
1
Q
What are the two major of anesthetic classes
A
- general
- local
2
Q
Describe the route of administration and primary actions general anesthetics:
A
Given either:
- inhaled
- IV
They primarily have CNS effect
3
Q
Describe the route of administration and primary actions local anesthetics:
A
Injected at the operative site to block nerve conduction
4
Q
What are the stages of general anesthesia?
A
- Stage I-Analgesia
- Stage II-Excitement
- Stage III-Surgical anesthesia
- Stage IV-Medullary paralysis
5
Q
Describe Stage I-Analgesia of general anesthesia:
A
- reduced sensation of pain
- the patient remains conscious and conversational
6
Q
Describe Stage II-Excitement of general anesthesia:
A
- delirium and combative behavior ensue
- there is an increase in BP and respiratory rate
7
Q
Describe Stage III-Surgical anesthesia of general anesthesia:
A
- the patient is unconscious, and regular respiration returns
- there is muscle relaxation and decreased vasomotor response to painful stimuli
8
Q
Describe Stage IV-Medullary paralysis of general anesthesia:
A
- respiratory drive decreases and vasomotor output diminishes
- death may quickly ensue
9
Q
How does the pharmacokinetics of anesthesia affect these stages?
A
- With slow-onset agents all four stages are discernible.
- Faster-acting agents allow for quicker progression through the stages.
10
Q
Give example of slow-onset agent:
A
- ether
11
Q
What is induction of anesthesia?
A
The time from administration of a general anesthetic to the achievement of surgical anesthesia
12
Q
What is induction of anesthesia dependent on?
A
How fast the anesthetics reaches the CNS
13
Q
How are the complications of anesthetics induction avoided?
A
An ultra-fast-acting, short-lived agent is given IV so that the patient will rapidly progress through the first and second stages of anesthesia
14
Q
What is recovery?
A
Simply, the reverse of induction
15
Q
What does recovery depend upon?
A
How quickly the anesthetics are removed from the CNS
16
Q
For inhaled anesthetics, what five factors influence the rate of induction?
A
- solubility
- pulmonary ventilation
- partial pressure of the inhaled agent
- alveolar blood flow
- arteriovenous concentration gradient
17
Q
Describe how solubility affects the rate of induction:
A
- The blood-gas partition coefficient is an index of solubility; a low coefficient implies relative insolubility.
- An agent with a low solubility requires fewer molecules to raise the partial pressure and arterial pressure is achieved rapidly, which leads to faster induction.
- Recovery likewise hastened when the anesthetic agent is discontinued.
18
Q
Describe how the partial pressure of the inhaled agent affects the rate of induction:
A
- An increased concentration in the inhaled air mixture leads to greater concentration at the alveoli and thus increase the partial pressure of the agent.
- In clinical practice, a greater concentration is given initially to speed induction, and then it is reduced to a maintenance level.
19
Q
How does alveolar blood flow affect the rate of induction?
A
Increased flow allows for more rapid uptake of the agent and quicker effect on the CNS.
20
Q
Describe how the arteriovenous concentration gradient affects the rate of induction:
A
This is dependent of the agent by tissue.
- A high rate and extent of tissue uptake will decrease the venous concentration of the anesthetic.
- As a result, it will take longer time for the anesthetic concentration of arterial and venous blood to equilibrate.
21
Q
What factors influence tissue uptake of an anesthetic?
A
Anesthetic uptake is influenced by many of the same factors that influence transfer from the lung to the blood; tissue-blood partition coefficients rates of blood flow to the tissues, and concentration gradients are all important factors.
- Highly perfused tissues (brain, heart, liver, kidneys, and splanchnic bed) will exert the greatest influence on arteriovenous concentration.
- Skin and muscle undergo slow diffusion because these tissues are less richly perfused and thus exert less of an effect on arteriovenous concentration.
22
Q
What is the molecular mechanism of action for general anesthetics?
A
The mechanism is not clear.
- All anesthetics have common property of increasing treshold of action potentials and inhibiting the rapid increase in the membrane permeability to sodium ions.
23
Q
Name 6 inhaled agents:
A
- Halothane
- Enflurane
- Isoflurane
- Desflurane
- Sevoflurane
- Nitrous oxide
24
Q
How is the potency of inhaled anesthetics defined and measured?
A
Using the concept of MAC
25
What is MAC
MAC is the minimum alveolar concentration of anesthetics necessary to eliminate movement among 50% of patients challenged by a standarized skin incision.
26
How does MAC relate to potency?
The greater the MAC of an agent, the greater the concentration needed to provide anesthesia.
- Thus an agent with high MAC has low potency
27
Give an example of an agent with high MAC (=low potency):
Nitrous oxide
28
How can the MAC of any inhaled agent be reduced?
By using the agent with conjunction with analgesics such as opioids or sedative hypnotics
29
Describe Halothane:
The first of the halogenated volatile anesthetics to be developed halothane has been largely replaced by more modern agents.
30
What is the clinical indications of Halothane?
Halothane is still used in the pediatric population because of its pleasant odor and lack of hepatotoxicity
31
Is Halothane metabolized?
ca. 20% is eliminated by metabolism; and the remainder is eliminated unchanged in expired air.
32
What is Halothanes MAC?
0,75%
33
What are the cardiovascular effect of Halothane?
Halothane sensitizes the myocardium to the effects of catecholamines (thus increasing the risk of arrythmias), decreases the heart rate and cardiac output, and leads to lowered BP and peripheral resistance.
34
Are there any toxic effects associated with Halothane?
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- hepatotoxicity
| - malignant hyperthermia
35
What is malignant hyperthermia?
A potentially fatal reaction to any of the inhaled anesthetics, which results in:
- hyperthermia
- metabolic acidosis
- tachycardia
- accelerated muscle contraction
36
How is malignant hyperthermia treated?
With Dantrolene and cessation of the offending agent
37
What is the clinical indication of Enflurane?
rapid induction of general anesthesia
38
Is Enflurane metabolized?
Ca. 2% of the agent is metabolized to a fluoride ion, which is then excreted in the kidneys. The rest is eliminated unchanged in the expired air.
39
What is Enflurane´s MAC?
1,6%
40
What are Enflurane´s cardiovascular effects?
- decreases heart rate, BP, and peripheral resistance
- it has a less sensitizing effect on the myocardium than does Halothane
- can produce cardiac arrythmias
41
Describe the toxic effects of Enflurane?
- The fluoride ion resulting from Enflurane´s metabolism can be nephrotoxic.
- A decrease in the kidneys concentrating ability after prolonged exposure to Enflurane has been observed in patients with preoperative kidney insufficiency.
42
What are the clinical indications of Isoflurane?
general anesthetics
43
Is Isoflurane metabolized?
Isoflurane is minimally metabolized; almost all of the drug is eliminated unchanged in the expired air
44
What si the MAC of Isoflurane?
1,4%
45
What are the cardiovascular effects of Isoflurane?
- increases heart rate
- does not effect cardiac output
- can lower BP and reduce peripheral vascular resistance profoundly
- does not sensitize the myocardium to catecholamines
- does not induce arrythmia
46
What are the toxic effects of Isoflurane?
potential for malingant hyperthermia
47
What are the clinical indications for Desflurane?
General anesthesia
48
Does Desflurane udnergo metabolism?
Desflurane is eliminated unchanged in expired air
49
What is Desflurane MAC?
6%
50
What are Desflurane´s cardiovascular effect?
Its profile very similar to that of Isoflurane
51
Are there toxic effects of Desflurane?
Potential for malignant hyperthermia
52
What are the clinical indications of Sevoflurane?
General anesthesia
53
Does Sevoflurane undergo metabolism?
A small percentage of this agent is metabolized to fluoride ion; the remainder is eliminated unchanged in the expired air
54
What is the MAC of Sevoflurane?
2%
55
Describe Sevoflurane´s cardiovascular effects:
It has a cardiac profile similar to that of Desflurane and Isoflurane
56
What are the toxic effects of Sevoflurane?
Although metabolism of Sevoflurane produces a fluoride ion, it does not affect renal function like enflurane does.
- It has been hypothesized that because Sevoflurane is not metabolized in the kidney (as enflurane is), toxic effect do not occur.
57
Laughing gas =
Nitrous oxide
58
What are the clinical indications of Nitrous oxide?
Induction of general anesthesia
59
How is Nitrous oxide administered?
Because of its low potency Nitrous oxide must be used in conjunction with other anesthetics (either inhaled or IV) for effective general anesthesia
60
Is Nitrous oxide metabolised?
Nope!
61
What is the MAC of Nitrous oxide?
100% - even if 100% Nitrous oxide was given to the patient, surgical anesthesia would not be achieved (and profound hypoxia would result)
62
Are there cardiovascular effects after using Nitrous oxide?
Nitrous oxide minimally affects the cardiovascular system
63
Name a major CI to the use of Nitrous oxide?
If Nitrous oxide is administered to patients who have closed air cavities (e.g pneumothorax), the gas will diffuse into the cavity and increase the pressure within it.
64
What special consideration should be taken into account during the recovery phase?
Care must be taken to adequately oxygenate the patient, because Nitrous oxide will diffuse from the blood to the alveoli so quickly that it entirely replaces oxygen, which results in diffusion hypoxia
65
What are the toxic effects of Nitrous oxide?
- bone marrow depression with prolonged administration
| - high concentrations may cause neuropathies
66
What are the classes of IV anesthetics?
- barbiturates
- benzodiazepines
- opioids
- dissociative agents
67
Ultra-short-acting barbiturates example:
Thiopental
68
What are the clinical indications for the use of Thiopental?
- Thiopental is used for the induction of anesthesia in combination with inhaled anesthetics.
- It has a rapid onset of action, with unconsciousness occuring 15-30 seconds after administration.
69
What is the mechanism of action of Thiopental?
- Thiopental binds the GABAa receptor which results in prolonged opening of the chloride channel.
- The neuron´s membrane is thus hyperpolarized, which creates a reduction in neuronal excitability.
70
What phenomenon is responsible for Thiopental fast onset of action and short duration?
Thiopental has high lipid solubility and thus crosses the blood-brain barrier very quickly.
- However the drug just as quickly diffuses out of the brain and other highly vascularized organs, and is rapidly redistributed to muscle, fat, and other body tissues, which accounts for its short duration.
71
Is Thiopental metabolised?
Yes.
- Metabolism (in the liver) occurs more slowly than redistribution.
- Nearly 99% of the metabolised drug; thus after large doses (especially continuous infusion), recovery can be very slow.
72
What are the cardiovascular effects of Thiopental?
Thiopental reduces BP and cardiac output, but it does not affect peripheral resistance.
73
Describe the respiratory rate after the use of Thiopental:
Thiopental depresses the respiratory center of the brain and blunts the response to CO2 and hypoxia.
- This effect on cerebral blood makes Thiopental a desirable agent in patients who have cerebral edema.
74
What are the effects of Thiopental on the cerebral blood flow?
- decreases blood flow
| - oxygen consumption in the brain
75
Are there any side effects with the use of Thiopental?
- may induce laryngospasm and bronchiospasm
- exacerbate acute intermittent porphyria by inducing the synthesis of hepatic δ-aminolevulinic acid synthase (thiopental has precipitated pophyric crisis)
76
Name some benzodiazepines:
- midazolam
- diazepam
- lorazepam
77
Describe the clinical uses of benzodiazepines:
- preoperative surgery
- intraoperative sedation for procedures not requiring analgesia
- As a apart of balanced anesthesia
78
Give examples of intraoperative sedation for procedures not requiring analgesia:
- colonoscopy
| - cardioversion
79
Balanced anesthesia def:
using several agents simultaneously to obtain surgical anesthesia
80
What is the mechanism of action of benzodiazepines?
Benzodiazepines binds GABA receptors, which results in reduced neuronal excitability.
- These drugs have a much slower onset of action than do the barbiturates.
81
Why is midazolam used as a preanesthetic medication?
Midazolam produces antegrade amnesia, which calms the patient
82
Antegrade amnesia def:
loss of memory of events after administration of the drug
83
Why is midazolam also the preferred benzodiazepine for induction and maintenance of anesthesia?
Midazolam has a shorter onset of action, greater potency, and more rapid elimination when compared to other benzodiazepines
84
What are the side effects of benzodiazepine?
- Alone, benzodiazepines can cause moderate circulatory and respiratory depression.
- If used with opioids, cardiovascular collapse and respiratory arrest can occur.
85
Are there other uses for benzodiazepine?
benzodiazepine is used to control seizures and in the alcohol withdrawal process to control symptoms
86
Is there a benzodiazepine antagonist?
Flumazenil antagonizes the CNS depression caused by benzodiazepine
87
Give examples of opioids:
- fentanyl
| - morphine
88
What are the clinical indications for opioids?
Opioids are used as general anesthetics in patients undergoing cardiac surgery or other major surgeries for which cardiac reserve is limited.
89
Why is fentanyl used more than morphine?
- greater potency
| - less impact on respiratory drive
90
What are the side effects of opioids?
- IV opioids can cause chest wall rigidity , which makes ventilation more difficult.
- Postoperative respiratory depression can occur.
- Intraoperative awareness with unpleasant postoperative recall may occur.
91
Is there an opioids antagonist?
Naloxone reverses the respiratory and CNS effects of opioids
92
What is Innovar?
Innovar is a combination of Fentanyl and Droperidol.
| - When used with Nitrous oxide, Innovar porduces neuroleptanesthesia
93
Neuroleptanesthesia def:
combined analgesia and amnesia
94
What are the clinical indications of Propofol?
Induction of anesthesia
95
What are the pharmacological characteristics of Propofol?
- Ultra-fast-acting drug with pharmacodynamics similar to those of Thiopental
- High lipid solubility
- Very quick distribution to highly vascularized sites (e.g. the brain)
- Rapid diffusion back into the blood, with subsequent redistribution.
96
Why is Propofol preferred over Thiopental for induction of anesthesia?
- Rate of onset very similar to Thiopental
- Recovery is quicker, with patients able to ambulate sooner than with other IV anesthetics.
- Patients report less nausea and emesis
- No cumulative effect from Propofol administration or delayed recovery after prolonged administration.
97
How is Propofol metabolized?
It is rapidly metabolized by the liver and other extrahepatic enzymes (10 times more quickly than Thiopental)
98
What are the side effects of Propofol?
- Hypotension
- Negative inotropic effects
- Pain at the site of injection
- Apnea
99
Does Propofol have any other uses?
Propofol is often used in the critical care settings as a continuous infusion to provide prolonged sedation
100
What are the clinical indications for Ketamine?
Ketamine, because of its unique cardiovascular effects, is used in trauma cases where cardiovascular support is necessary.
- It is also used in children undergoing painful procedures (dressing changes of burns) or to facilitate cooperation during radiographic procedures
101
What is the mechanism of action of Ketamine?
Ketamine produces dissociative anesthesia characterized by catatonia, amnesia, and analgesia without the actual loss of consciousness
102
What are the cardiovascular effects of Ketamine?
- Ketamine is unique in that it produces cardiovascular stimulation, with HR, arterial BP, and CO all usually significantly increased.
- Ketamine stimulates the sympathetic nervous system, which causes the release of catecholamines
103
Is Ketamine used in head trauma cases?
No, because it increases the cerebral blood flow, oxygen consumption, and intracranial pressure.
104
What are the side effects of Ketamine?
- can cause an emergence phenomenon consisting of disorientation, sensory and perceptual illusion, and vivid, often unpleasant dreams.
105
What can be done to reduce the phenomenon that occurs when taking Ketamine?
Use of Diazepam 5-10 min before Ketamine administration.
106
Are there other routes of administrating Ketamine?
- IM
| - IV
107
What are the two types of local anesthetics?
The two classes are determined by the bond linking the lipophilic portion of the molecule with the hydrophilic components
- ester bond, or
- amide bond
108
Name the ester anesthetics:
- cocaine
- benzocaine
- procaine
- tetracaine
109
Name the amide anesthetics:
- lidocaine
- mepivacaine
- bupivacaine
- prilocaine
110
How does the metabolism of ester and amide anesthetics differ?
- Esters are more rapidly metabolised by blood and tissue esterase, which gives them short half-lives.
- Amides are metabolised by hepatic microsomal enzymes, which results in longer half-life.
111
What is the mechanism of action of local anesthetics?
These agents block the nerve conduction by inhibiting the voltage-gated sodium channels of the neuronal membrane
112
Which nerve fibers are the most sensitive to local anesthetics?
- Small, unmyelinated fibers that conduct pain, temperature, and autonomic activity that are affected first.
- With increasing concentrations of anesthetic, pain fibers (C and A fibers) are first affected, then sensory fibers (A fibers), and last motor neurons (A fibers)
113
What are the clinical indications for local anesthetics?
Used for:
- Surface anesthesia
- Nerve blocks
- Spinal and epidural anesthesia
- Lidocain is also a potent antiarrythmic
114
How is the duration of local anesthetics increased?
Adding epinephrine to local anesthetics reduces blood flow to the anesthetized area, thus decreasing the absorption of the drugs and enhancing their duration of action
115
What are the side effects of local anesthetics?
Systemic effects of local anesthetics occurs with high doses of the drug:
- CNS disturbances (light-headedness, sensory distrubances, convulsion, coma, and even death at high doses)
- Cardiovascular effects (myocardial depression and hypotension except for cocaine, which causes vasoconstriction and hypertension)
