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83 Cards in this Set
- Front
- Back
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What are 3 benefits that inhaled anesthetics offer over IV drugs?
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1. Rapid onset and short duration of action
2. Easy to monitor end-tidal gas measurement that is assumed to mirror brain concentration 3. Majority of elimination is via the lungs which makes elimination virtually independent of hepatic or renal function |
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Which two drugs are completely fluorinated?
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Des and sevo
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What does halogenating/fluorinating the drugs do?
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less toxic, nonflammable, less soluble in blood
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Who discovered nitrous oxide?
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Horace Wells
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Who discovered diethyl ether
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William Morton
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Who discovered Chloroform
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James Simpson
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What drugs were used from 1920-1940?
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Ethylene, cyclopropane, divinyl ether (lower solubility)
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What drugs vanished from clinical practice due to their flammability?
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Ethylene, divinyl ether,diethyl ether, and cyclopropane
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Why did chloroform disappear from practice?
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Hepatotoxicity
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What happened during 1960-1990 with inhaled anesthetics?
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-Halogenated agents synthesized
-Addition of chlorine, bromine, fluorine ions -inflammability |
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Substitution of fluorine for bromine or chlorine provided for?
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less toxicity and less solubility
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What was the prototype agent?
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Halothane
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What two agents became the mainstays of anesthetic delivery in the 1970s and 1980s?
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Enflurane - #347
Isoflurane- #469 |
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Desflurane was the first agent?
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halogenated exclusively with fluorine
#653 |
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What were potential limitations of Desflurane early on?
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1. synthesized with elemental fluorine in a potentially explosive process
2. saturated vapor pressure near one atmosphere precluded its use with conventional vaporizers |
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Desflurane is _____ potent as isoflurane
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1/5
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When was sevoflurane originally synthesized? Why didn't it go into use then?
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1960s, like des it was expensive and difficult to synthesize- concern existed over Compound A
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When was des and sevo reconsidered for commercial development?
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In the 1980s
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Why was it reconsidered then?
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Outpatient and ambulatory surgery ann anesthesia were emerging
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Halogenation of inhaled anesthetics exclusively with fluorine produced a lower?
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blood solubility and a shorter acting agent
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When was Desflurane approved for use in the US?
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1992, much safer synthetic process developed
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Vapor pressure
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is the pressure exerted by a gas above a liquid when the two are in equilibrium (exerting the same partial pressures)
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As temperature increases, vapor pressure?
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increases
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What happens if an agent with a higher vapor pressure is mistakenly added to a vaporizer of an agent with a lower vapor pressure?
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It would be delivering a more concentrated dose
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Anesthetic degradation
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present day carbon dioxide absorbents can degrade all halogenated anesthetics
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Why is anesthetic degradation a concern?
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Potential toxicity (CO and Compound A), theoretical loss of anesthetic (delay in induction of anesthesia)
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Degradation depends largely on two factors
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1. Moist vs. dry soda lime (dessicated)
2. Temperature of the soda lime |
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With moist soda lime, Desflurane will show degradation at what temperature?
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slight at 80 degrees C, no degradation at 40 or 60 degrees C
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With moist soda lime, Isoflurane will show degradation at what temperatures?
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moderate at 80 degrees C, no degradtion at 40 or 60 degrees C
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With moist soda lime, halothane will show degradation at what temperatures?
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Same as Isoflurane
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With moist soda lime, sevoflurane will show degradation at what temperatures?
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1. Slight degradation at 40
2. Considerable degradation at 60 3. Massive degradation at 80 |
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What can you conclude about sevoflurane in regards to degradation of moist soda lime?
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It is more reactive at normal temperatures
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Degradation of anesthetic is due to interaction between the?
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anesthetic and the monovalent bases in the carbon dioxide absorbent
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What are the monovalent bases?
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NaOH and KOH
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Is there degradation by the divalent bases? What are they?
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No, CaOH and BaOH
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How do you get dry soda lime?
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HIgh flow rates over extended period of time
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With dry soda lime, studies have shown that des and iso degrade at what temperatures?
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40, 60, and 80
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Dry soda lime and sevoflurane
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The rate of degradation of sevo also increases markedly
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More so with dry soda lime vs moist, significant degradation may limit?
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the delivery of anesthetic
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What occurs between dessicated carbon dioxide absorbents and inhaled anesthetics?
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Profound exothermic reactions
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What temperatures are achieved at same MAC concentrations with dessicated absorbent?
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Des- 57
Iso- 78 Sevo - 128 |
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What has been reported with the use of a dessicated absorbent and sevo?
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fire in the anesthetic breathing circuit
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What happened in a study where 1.5 MAC sevo administered using dessicated Baralyme?
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1. In 30-70 minutes temperatures exceeded 200
2. Flames appeared in breathing circuit in 2 of 5 models 3. Des and Iso produced significant heating but no fire |
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How might you know if you have dessicated absorbents?
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unusual rise in FI or rapid color change
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What is produced from Sevoflurane as a result of using dessicated absorbents?
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Compound A
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What is produced from Desflurane or Isoflurane as a result of using dessicated absorbents?
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Carbon monoxide
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With compound A, where is the target of injury?
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corticomedually junction of the kidney
-dose related enzymuria, proteinuria, renal necrosis demonstrated in rats |
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What is produced as a result of degradation of sevoflurane by carbon dioxide absorbents?
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Vinyl ether
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T or F. Debate continues concerning nephrotoxic potential of compound A in humans.
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True
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Concentrations of compound A breathed by patients vary as a function of several factors, what are they (3)?
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1. Correlate directly with sevoflurane concentration
2. Correlate directly with absorbent temperatures 3. Correlate inversely with FGF rates |
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What is the recommended flow rates to avoid toxicity of compound A?
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1. FGF rate of 1 LPM for up to 2 MAC hours
2. FGF rate of 2LPM after 2 MAC hours |
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Higher FGF rates reduce?
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rebreathing of CO2 and less contact with absorbent
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Carbon monoxide
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is a breakdown product of inhaled anesthetics and dessicated absorbents
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What two agents are most avidly degraded to CO?
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Desflurane and Isoflurane
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Production of significant amount of CO requires what % dessicated absorbent?
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90%
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The reaction results from the action of ________ in the absorbent?
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monovalent bases
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Are there any reports of patient injury as a result of CO toxicity?
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no
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Define MAC
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the minimum alveolar concentration of inhaled anesthetic that produces immobility in 50% of humans when exposed to a noxious stimulus
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Does MAC differ significantly across a myriad of species?
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No, small differences
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MAC is a measure of?
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anesthetic potency, inversely related
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What mediates MAC, brain or spinal cord?
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spinal cord
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Surgical anesthesia approximates ___ MAC.
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1.3, 95% immobility
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MAC awake
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the average concentration permitting voluntary response to command
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Why is MAC awake a good depth of anesthesia?
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emergence point, safety (protecting airway), exceed amnestic point
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MAC awake/MAC ratio
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For des, iso, and sevo, MAC awake is approximately 1/3 of MAC
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MAC BAR
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Alveolar concentration that Blocks Autonomic Response
-approximates 1.5 MAC |
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Meyer-Overton hypothesis
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anesthetic potency correlates directly with lipid solubility
-anesthetic disrupts neuronal transmission at hydrophobic sites in the lipid bilayer |
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5-Angstrom theory
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-suggest anesthetics act by an action on two sites separated by a distance of 5 angstroms (working in and out of the lipid bilayer)
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In the 5-angstrom theory, potency increases....?
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to a maximum at a 5 carbon length, at which time potency markedly decreases
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Receptor/Neurotransmitter interaction
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-evidence that inhaled anesthetics depress excitatory receptors (serotonin, Ach, glutamate) and enhance inhibitory receptors (GABA, glycine)
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What is the ultimate goal of anesthesia?
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To achieve a constant partial pressure of anesthetic in the CNS
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To achieve a constant partial pressure it must be attained in the?
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alveoli
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Anesthetic uptake from the lungs is a product of 3 factors?
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1. Solubility
2. Cardiac Output 3. Alveolar-venous partial pressure gradient |
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solubility of anesthetic gas in the blood is denoted by?
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blood: gas partition coefficient
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What does the blood:gas partition coefficient describe?
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the affinity of the anesthetic for two phases at equilibrium
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Solubility describes how the anesthetic will?
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partition itself between the liquid and the gas phase
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If the blood:gas partition coefficient is 2,then at equilibrium, then?
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the concentration in the blood will be twice that in the gas phase
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What does a larger blood:gas partition coefficient indicate? And will have what effect on FA/FI ration?
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a greater solubility, will produce a lower FA/FI ratio
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What are the blood:gas partition coefficients at 37 C? For Des, N20, Sevo, Iso, Halothane.
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Des: 0.42
N20: 0.47 Sevo: 0.69 Iso: 1.4 Halothane: 2.4 |
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What is the SVP at 20C for Des, Sevo, Iso, and Halothane?
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Des:700
Sevo: 157 Iso: 240 Halo:244 |
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What are the MAC values in 100% O2 for Halo, Iso, Sevo, Des, N20?
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Halo:0.75%
Iso:1.2% Sevo: 2.0% Des: 6.0% N20: 105% |
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What are the MAC values in 70% N20 for Halo, Iso, Sevo and Des?
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Halo: 0.29%
Iso: 0.50% Sevo: 0.66% Des: 2.8% |
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Surgical anesthesia approximates what MAC value?
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1.3 of 95% have immobility
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