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43 Cards in this Set
- Front
- Back
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Definition of anesthesia
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drug-induced absence of perception of all sensations
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Depth of anesthesia
a. stage I b. II c. III d. IV |
a. decreased perception, calm, some analgesia
b. excitement, delirium, irregular respiration, amnesia c. surgical - regular breathing or no breathing, no perception d. coma, no spontaneous breathing or movement, depressed/flat EEG (BAD) |
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What factor determines the speed at which an anesthtic reaches adequate blood levels to have effect
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blood gas coefficient
if low, then gas has low solubility in blood --> high partial pressure --> high concentration --> rapidly reaches adequate blood level |
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5 factors that determine the concentration of anesthesia that gets to the alveoli
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1. Amount of inspired gas (Fi)
2. Pulmonary ventilation 3. Gas solubility 4. Pulmonary blood flow 5. Arteriovenous concentration gradient 5. Movement from alveoli to arterial circulation |
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How does the concentration of given anesthetic lead to increased rate of induction of anesthesia
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Higher partial pressure of anesthesia --> higher conentration gradient between alveoli and blood --> more gets to brain
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How does pulmonary ventilation affect the amount of anesthetic
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With continuous infusion, more gas is taken up by the blood as the rate or tidal volume of breathing increases
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What is the relationship between the rate of induction/recovery and the solubility of a drug
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Inverse - as solubility goes up, induction/recovery goes down
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How does pulmonary blood flow affect the amount of anesthesia available
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High blood flow --> less buildup of gas in the alveoli
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What creates the AV gradient of anesthetic gas?
Why is this important? |
Uptake in peripheral tissues creates AV gradient
Need gradient so that anesthetic gas will be taken up in the pulmonary circulation from the alveoli |
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Relationship between inhaled and alveolar gas conc.
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FA/Fi < 1
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Relationship between arterial and alveolar gas conc. on induction
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Fa/FA < 1
arterial accumulation lags behind alveolar accumulation; made worse by ventilation-perfusion mismatches (pneumonia, atelectasis, PE) |
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Mechanism by which most inhaled anesthetics are eliminated
Factors that affect this process |
Once conc. gradient is reversed, gas diffuses back into alveoli, expired
Rate of elimination increased by low blood solubility, low V/Q mismatch, increased ventilation |
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Which drug is extensively metabolized
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halothane
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Order of metabolism of inhaled anesthetics
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halothane > sevoflurane > isoflurane > desflurane > nitrous oxide
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What is the second gas effect
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High volume uptake of one gas can increase the FA (alveolar conc) of a second gas, thereby increasing its uptake as well
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2 drugs that exhibit the second gas effect
In what clinical circumstance is this used |
Nitrous oxide and sevoflurane
Pediatric inhalations in which child has no IV access |
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What is the MAC
Sign of potency? |
Minimal alveolar concentration = measure of anesthetic gas at which 50% of patients will not move in response to a noxious stimuli
Low MAC --> more potent |
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MAC of NO
How is it used normally |
MAC > 100
Used to supplement other anesthesias via 2nd gas effect, given with IV opioids in minor surgeries (dental, etc) |
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What is the favorable pharmacokinetic property of NO
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Low blood:gas coefficient --> rapid onset and recovery
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Contraindications for NO
Why are these contras? |
Pneumothorax, acute intestinal obstruction, suspected air embolus, intracranial air, tympanic membrane grafting
NO can fill any air filled cavity 3x faster than air can diffuse out of cavity into blood |
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Context of halothane use
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pediatrics (becaue of its pleasant odor?)
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How is halothane metabolized?
One potential side effect of use |
hepatic
autoimmune hepatitis in adults |
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Halothan propoerties
a. speed b. potency |
a. soluble, so slow induction and emergence
b. low MAC --> potent |
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What has historically been the #1 inhalation anesthtic used in adults
What 2 drugs have since bypassed it |
isoflurane
sevoflurane and desflurane |
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Drug with the lowest blood: gas partition coefficient
Benefits of this property |
Desflurane
rapid control over depth of anesthesia (eliminated completely in lungs), rapid emergence |
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Contraindications for desflurane
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Children (rapid emergence can lead to delirium), asthmatics or smokers (causes airway irritation)
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Property of desflurante that precludes its use in inhalation inductions
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highly pungent
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How is sevoflurane different from desflurane
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-more soluble (slower)
-less airway irritability -more pleasant smell --> can use in pediatrics |
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Contraindications of sevoflurane
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renal dysfunction
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4 drugs that decrease mean arterial pressure
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halothane
isoflurane desflurane sevoflurane |
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3 drugs that increase heart rate --> maintain cardiac output
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isoflurane
desflurane sevoflurane |
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drug with minimal CV effects
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NO
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What are the effects of general anesthetics effect on the respiratory system
exception |
decrease minute ventilation, depress respiratory response to hypoxia and hypercarbia
Except NO |
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What is the effect of anesthetic gases on the CNS?
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Luxury perfursion = decrease cerebral metabolic activity while increasing blood flow
--> raise ICP (bad in neursurgical patients) |
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Effect of anesthetic gases on kidneys
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Decrease GFR and urine output (due to decrease in CO and BP)
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What is the effect of anesthetics on the liver
One drug that is specifically worse than the others with the liver |
decrease hepatic blood flow
Halothane is hepatotoxic, can have effects even after recovery from anesthesia |
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What is a potentially lethal toxic side effect of anesthetics
What is the exception drug that does not cause this |
Malignant hyperthermia (also caused by succinylcholine)
NO does not cause this |
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Patient was given an inhalation anesthetic, now experiences:
Tachycardia, hypercarbia, hypertension, acidosis, hyperkalemia, increasing muscle rigidity, severe hyperthermia Dx? How do you proceed? |
Malignant hyperthermia = acute hypermetabolic state
1. stop anesthetic 2. cool patient 3. IV hydration 4. IV dantrolene (Ca channel antagonist) |
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Patient experiences severe hyperthermia and muscle rigidity after taking succinylcholine (depolarizing muscle relaxant)
What genetic mutation does the patient have that predisposes them to this reaction |
Malignant hyperthermia
Mutation in the ryanodine receptor (Ca channel in SR), autosomal dominant inheritance |
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Patient has mutation in the ryanodine receptor
How should you proceed with general anesthesia? What are you trying to avoid |
Malignant hyperthermia
Give NO + IV anesthetic Avoid succinylcholine |
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What is the mechanism of action of anesthetics
Meyer-Overtone principle -- status of theory |
Decrease neuronal activity by raising the electrical threshold for firing
Theory debunked - people now think anesthetics bind to specific protein targets More lipid soluble anesthetics are more potent |
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How do volatile anesthetics work
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Depress excitatory glutamate receptors (NMDA) and enhance inhibitory NTs (GABA and glycine)
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NO
Halothane Desflurane Isoflurane Sevoflurane Rate most potent to least potent (MAC) Rate fastest to slowest |
halo > iso > sevo > des > NO
des > NO > sevo > iso > halo |
