Neuroscience Week 3: Anesthetics Flashcards
(181 cards)
1
Q
Be able to explain the stages of inhalational anesthesia and the pharmacokinetics of inhaled anesthetics (alveolar wash-in, uptake from the lungs, solubility in blood, tissue uptake, and elimination), including the concept of minimum alveolar concentration.
A
2
Q
Be able to describe the mechanisms of action (including analgesic properties) and organ system effects (including effects on intracranial pressure) of inhaled and intravenous anesthetics, the uses of these agents and their adverse effects, including malignant hyperthermia and its treatment.
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3
Q
Be able to list the key differences between amide and ester local anesthetics, as well as to explain in detail the mechanism of action of local anesthetics, the influence of pH on their actions, which nerve fibers are more or less sensitive to them (e.g., small unmyelinated fibers are the most sensitive to block), their uses and adverse effects.
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4
Q
Balanced Anesthesia Definition
A
Combination of inhaled anesthetics and IV medications
5
Q
Monitored Anesthesia Definition
A
Oral or parenteral sedatives + local anesthetics
6
Q
Conscious Sedation Definition
A
Alleviation of anxiety and pain + altered levels of consciousness produced by small doses of sedatives (in ICU, neuromuscular blockers may be also used)
7
Q
Deep Sedation Definition
A
Light state of anesthesia (also used in ICU)
8
Q
Depth of Anesthesia: Stage I
A
Analgesia and subsequent amnesia.
9
Q
Depth of Anesthesia: Stage II
A
Excitement
- delirium, combative behavior, increase in blood pressure and respiratory rate. To avoid, a shortacting I.V. anesthetic is given before.
- in part due to inhibition of the function of inhibitory neurons in the brain, excitatory neurons are disinhibited
10
Q
Depth of Anesthesia: Stage III
A
Surgical Anesthesia
regular respiration, skeletal muscle relaxation, decrease in eye reflexes and movements, fixed pupils. Loss of motor and autonomic responses to pain.
11
Q
Depth of Anesthesia: Stage IV
A
Medullary Paralysis
depression of respiratory and vasomotor centers. can be followed by Death.
12
Q
Neuron type sensitivity to anesthesia
A
- Dorsal horn = analgesia
- Frontal cortex = sedation
- Thalamic neurons and midbrain reticular formation = hypnosis
- Ventral horn = immobility
13
Q
MAC
A
- Potency of anesthetics is measured in minimum alveolar concentrations
- Potency is an expression of the activity of a drug in terms of the concentration or amount of the drug required to produce a defined effect,
- Efficacy. maximum effect that a drug can produce regardless of dose
In these examples NO is least potent and Isoflurane is the most potent example given on this slide
14
Q
1 MAC
A
Alveolar concentration of anesthetic that renders immobile 50% of subjects exposed to a strong noxious stimulation
15
Q
MAC examples
A
16
Q
0.3 MAC
A
Analgesia
17
Q
0.5 MAC
A
Amnesia
18
Q
1.0 MAC
A
50% immobile
19
Q
1.2 MAC
A
Sympathetically-mediated response to surgery is blunted
20
Q
1.3 MAC
A
99% immobile
21
Q
>/= 2.0 MAC
A
Potentially lethal
22
Q
Most common Inhalational Anesthetics
A
- Sevoflurane (Volatile)
- Desflurane (Volatile)
- Isoflurane (Volatile)
- Nitrous Oxide (Gaseous)
23
Q
Most common Intravenous Anesthetics
7 listed
A
- Benzodiazepines (Midazolam)
- Opioids (Fentanyl)
- Barbiturates (Thiopental)
- Propofol
- Ketamine
- Etomidate
- Dexmedetomidine
24
Q
Pharmacokinetics of anesthesia
A
*higher the ventilatory rate/depth = shorter induction time
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Blood solubility of anesthesia
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Anesthetic type high arterial pressures are reached rapidly and shorter induction time
with an anesthetic w/ Low blood solubility
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Anesthetics Tissue Uptake
also remember Meyer-Overton rule
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Meyer-Overton rule
the higher the lipid solubility the more potent the anesthetic
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Anesthetic Elimination
clearance by the lungs is the main elimination route
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the rate of recovey from anesthesia depends on
the rate of elimination of the brain
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bronchospasm and anesthesia
avoid pungent agents in patients with bronchospasm
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malignant hyperthermia
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Malignant Hyperthermia Etiology
* Autosomal dominant genetic disorder
* Caused by mutations of muscle ryanodine receptor that are activated by inhaled anesthetics, leading to uncontrolled release of Ca2+ from the sarcoplasmic reticulum
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Malignant Hyperthermia Clinical Presentation
Characterized by tachycardia, hypertension, severe muscle rigidity, hyperthermia, hyperkalemia and acidosis
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Common when volatile anesthetics are combined with succinylcholine
Malignant hyperthermia
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Malignant Hyperthermia common anesthesia cause
Common when volatile anesthetics are combined with succinylcholine
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Malignant Hyperthermia Treatment
* Treatment = dantrolene (blocks Ca2+ release via ryanodine receptor);
* cooling;
* oxygen;
* correction of acid-base disturbances.
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Example of Antagonist of Ryanodine Receptor
Dantrolene
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How are different classes of anesthesia used in Balanced Anesthesia
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Balanced Anesthesia Premedication
Midazolam (I.V. Benzodiazepine)
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Balanced Anesthesia Induction reagents
Fentanyl IV opioid
Propofol IV anesthetic
**Cura**re-like neuromuscular blocker (nondepolarizing blocker) (Pan**curo**nium)
Tracheal intubation
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Balanced Anesthesia Maintenance Reagents
Inhalational anesthetics
Sevoflurane 1-2% + Nitrous Oxide 66%
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TIVA AKA
Total intravenous Anesthesia
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Total Intravenous Anesthesia Premedication
Midazolam IV benzo
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Total Intravenous Anesthesia Induction Reagents
* Remifentanil (loading dose)
* Propofol
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Total Intravenous Anesthesia NMJ Blockade reagents
Rocuronium
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Total Intravenous Anesthesia Maintenance Reagents
* Remifentanil
* Propofol
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Total Intravenous Anesthesia complete procedure and reagents
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After what reagent is a patient intubated?
NMJ Blockers
Rocuronium TIVA
Pancuronium Balanced Anesthesia
(Curare-like)
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for what procedures can IV anesthetics used for?
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Volatiles Mech. of Action
↑GABAAR, ↓NMDAR & CNS nAChRs
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\*N2O Mech. of Action
↑GABAAR, ↓NMDAR,
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Midazolam Mech. of Action
↑ GABAAR
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\*Fentanyl Mech. of Action
R ↑ Opioid Rs
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Thiopental Mech. of Action
↑ GABAAR
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Propofol Mech. of Action
↑ GABAAR
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Etomid. Mech. of Action
↑ GABAAR
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Ketamine Mech. of Action
↓NMDAR
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Dexmet Mech. of Action
α2 -adrenoceptor agonist
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Volatiles Cardiovascular
* ↓Peripheral resistance
* ↓Myocardial O2 consumption
* Dilate coronaries
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N2O Cardiovascular
↓Myocardial function
↑Sympathetic (effects cancel out-minimal effect)
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Midazolam Cardiovascular
↓Peripheral resistance
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Fentanyl Cardiovascular
↓Heart rate
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Thiopental Cardiovascular
↓Peripheral resistance and myocardial contractility
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Propofol Cardiovascular
↓Peripheral resistance
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Etomidate Cardiovascular
Stability
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Ketamine Cardiovascular
↑Peripheral resistance and heart rate
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Dexmedetomidine Cardiovascular
↓Peripheral resistance and heart rate
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Volatiles Respiratory
* Depression.
* ↓Response to hypoxia.
* ↓Mucociliary.
* Bronchodilation
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N2O Respiratory
* Diffusional hypoxia.
* Diffuse into cavities (pneumothorax; also bowel loop).
can lead to increased pressure of the thorax or intestines
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Midazolam Respiratory
Depression (particularly when given with opioids)
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Fentanyl Respiratory
* Depression.
* ↓Response to hypoxia.
* Chest wall and laryngeal rigidity.
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Thiopental Respiratory
Depression.
↓Response to hypoxia.
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Propofol Respiratory
Depression.
↓Response to hypoxia.
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Etomidate Respiratory
Less pronounced depression.
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Ketamine Respiratory
Stable but laryngospasm can occur
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Dexmet Respiratory
Little effect
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Volatiles GI
Nausea/vomiting
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N2O GI
Nausea/vomiting
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Midazolam GI
N/A
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Fentanyl GI
Nausea Constipation
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Thiopental GI
Nausea/ vomiting
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Propofol GI
Antiemetic
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Etomidate GI
N/A
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Ketamine GI
N/A
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Dexmedetomidine GI
N/A
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Volatiles CNS
* ↓Metabolic rate
* ↑Cerebral blood flow and intracranial pressure
*
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N2O CNS
↑Cerebral blood flow and intracranial pressure via sympathetic
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Midazolam CNS
N/A
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Fentanyl CNS
↑ intracranial pressure in head trauma patients
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Thiopental CNS
* ↓Metabolic rate
* ↓Cerebral blood flow & intracranial pressure
* decreases metabolic rate and decreases cerebral blood flow and intracranial pressure which can be neuroprotective
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Propofol CNS
↓Metabolic rate.
↓Cerebral blood flow & intracranial pressure.
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Etomidate CNS
↓Metabolic rate.
↓Cerebral blood flow & intracranial pressure.
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Ketamine CNS
↑Metabolic rate.
↑Cerebral blood flow & intracranial pressure.
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Dexmedetomidine CNS
↓Cerebral blood flow but little effect on intracranial pressure
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Volatiles Liver/ Kidneys
↓blood flow
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N2O Liver/ Kidneys
↓blood flow
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Midazolam Liver/ Kidneys
Failure slows elimination
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Fentanyl Liver/ Kidneys
Caution in liver failure
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Thiopental Liver/ Kidneys
N/A
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Propofol Liver/ Kidneys
N/A
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Propofol Liver/ Kidneys
Failure slows elimination
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Etomidate Liver/ Kidneys
(Adrenocortical suppression)
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Ketamine Liver/ Kidneys
N/A
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Dexmet Liver/ Kidneys
N/A
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Volatiles Uterus
* ↓contraction
* can be useful if you need to do an emergency C-section
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Anesthetics that increase intracranial pressure
have to be careful with patients with intracranial injuries
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decreases metabolic rate and decreases cerebral blood flow and intracranial pressure which can be neuroprotective
* Thiopental
* Propofol
* Etomidate
DONT use Ketamine because it does the opposite
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Local Anesthetic classes
Esters (1 I)
Amides (2 I's)
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Esters
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Amides
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Esters Medium Duration
Cocaine
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Amides Medium Duration
Lidocaine
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Esters Short Duration
Procaine
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Esters Long Duration
Tetracaine (2 a's)
116
Amides Long Duration
Bupivacaine (2 a's)
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Local anesthetics lipophilic
Lipophilic agents are more potent and longer lasting for esters and amides alike
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Esters Metabolism
Hydrolized plasma esterases
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Amides Vs Esters
Amides are longer lasting
120
Local Anesthetics Mechanism of Action
* Mechanism of Action: open channel blockers of voltage-gated sodium channels
* Local anesthetics block from the inside when channel is open; fibers with high firing frequency are blocked first (i.e. pain fibers)
* Decrease action potential propagation. Cause nerve conduction to fail.
121
Local Anesthetics are dependent upon?
pH
only the uncharged base can cross the membrane
the charged form will go and blocks the channel from the inside
122
Local Anesthetics and Henderson Haselbach EQ
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Local Anesthetics Caveats
REMEMBER!!!!!!!!!!
In general, smaller fibers are blocked more easily than larger fibers, and myelinated fibers are blocked more easily than unmyelinated fibers.
* Activated pain fibers fire rapidly; thus, pain sensation appears to be selectively blocked by local anesthetics.
* Fibers located in the periphery of a thick nerve bundle are blocked sooner than those in the core because they are exposed earlier to higher concentrations of the anesthetic.
Order of blockade: Pain (fibers have high firing rate and long action potentials) →Other sensations → Motor
124
Concurent injection of ________ with local anesthetics
Epinephrine
It causes vasoconstriction via activation of α1 adrenergic receptors, decreasing removal of the local anesthetic via absorption into circulation. This increases duration of the local anesthetic’s effect
2. It activates presynaptic α2 adrenergic receptors, decreasing release of pain mediators such as Substance P
3. It provides local bleeding control (vasoconstriction)
125
Adverse Effects of Local Anesthetics
Restlessness and tremor. At high doses: convulsions (pre-medicate with benzodiazepine but could mask serious reactions), respiratory depression.
Neurotoxic injury. • Transient neurological symptoms (transient pain or dysesthesia) has been linked to lidocaine in spinal anesthesia.
Allergy - Especially, **ester**-type local anesthetics (very important)
126
Cardiovascular Adverse Effects of Local Anesthetics
Lipid Emulsion can act as a sink and remove and sequester anesthetics
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Local Anesthetics Overview Table
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Question 1
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Question 2
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Question 3
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Question 4
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Question 5
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Question 6
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Question 7
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Question 8
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Question 9
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Question 10
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Question 11
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Question 12
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Question 13
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Question 14
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Question 15
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Question 16
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MAC to %anesthetic
1 MAC = 100% N2O so .3 MAC = 30% N2O
1 MAC = 1.4% Isoflurane so .3 MAC = .42% Isoflurane
145
Alveolar Wash-in
↑Ventilatory rate/depth = shorter time to exchange lung gases with anesthetic mixture
increase the concentration and increase the depth of ventilation
146
If you need to anesthetize quickly choose?
an anesthetic with a low blood solubility because high arterial pressures are reached rapidly and shorter induction
147
Which tissues absorb Anesthetic most quickly
* highly perfused tissues rapidly achieve a steady-state with the partial pressures in blood
* muscles accumulate anesthetics more slowly due to lower perfusion rates and larger volume
* Adipose tissue accumulates anesthetics more slowly due to lower perfusion rates but most anesthetics have high lipid solubility (patient will recover from anesthesia less quickly)
148
the higher the lipid solubility of the anesthetic the more _______ is
Potency
so
the
lower
the
MAC
Potency is inversely related to MAC
149
Major route of anesthetic clearance from the body
unchanged by the lungs
150
Avoid pungent anesthetics in patients with
Bronchospasm
151
Pungent
Very strong odor but sensitive
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Ach Antagonist Malignant Hypothermia
wont work because the Ca2+ release is from inside the cell
153
Opioids
larynx rigidty preventing intubation, tracheostomy , naloxone antidote!
154
Benzodiazepines
155
Barbiturate anesthetics: Thiopental
rapid ultra short-acting
156
Propofol
milk of amnesia
antiemetic (postoperative vomiting is uncommon)
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Propofol intracranial pressure
↓Intracranial pressure
158
Propofol analgesic properties
not a good analgesic
159
Ketamine
160
Only IV anesthetic that produces cardiovascular stimulation (increases heart rate and cardiac output)
Ketamine
161
Ketamine analgesic properties
good analgesic
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Ketamine respiratory effects
minimal effects on respiration
upper airway reflexes
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Don't give ketamine to patients with?
patients with cardiovascular issues or vascular issues stroke, psychosis or schizophrenia
164
Etomidate
165
Etomidate Caveat
can use in anesthetic induction in patients at risk of hypotension because it produces minimal cardiovascular and respiratory depression
166
Etomidate Side effects
* Vomiting
* pain on injection
* Myoclonus
* Decreases plasma levels of hydrocortisone
167
Dexmedetomidine
used for short term sedation of intubated and ventilated ICU patients or during regional anesthesia
168
For an opiod tolerant patient what type of anesthesia
propofol perhaps
169
Two Is
Amide Local anesthetics
170
Two As
long-acting local anesthetic
171
How to treat arrhythymias from local anesthetics
lipid resuscitation
172
pH has a major effect on?
Local anesthetic effect
173
If patient has liver problems would an amide be appropriate
maybe not or decrease the dose
because amides are metabolized in the liver
174
where do local anesthetics have their therapeutic effect
on the internal Na+ channels
175
pH can block local anesthetics where?
intra and extracellularly because if it is charged it cannot get in
if it is not charged inside the cell then it cannot block the channel
176
Actions of local anesthetics
177
Why do you coinject with epinephrine
#1 is extremely important
178
aspirate before
putting in a local anesthetic
179
Pre-medicate with ____________ to prevent convulsions but it could mask serious reactions
benzodiazepines
180
Adverse effects of local anesthetics
IV Lipid Emulsion
181
lidocaine is used to treat \_\_\_\_\_
ventricular arythmias maybe
