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94 Cards in this Set
- Front
- Back
what general anesthetic is a gas?
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nitrous oxide
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isoflurane
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general anesthetic (volatile liquid)
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desflurane
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general anesthetic (volatile liquid)
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sevoflurane
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general anesthetic (volatile liquid)
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stage I of anesthesia
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"analgesia"
- analgesia - amnesia - euphoria |
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stage II of anesthesia
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"Excitement"
- excitement - delirium - combative behavior **like a bad nightmare** |
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stage III of anesthesia
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"Surgical Anesthesia"
- unconsciousness - regular respiration - decreasing eye movement |
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stage IV of anesthesia
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"Medullary Depression" = OD
- respiratory arrest - cardiac depression and arrest - no eye movement |
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list the stages of anesthesia experienced by a patient as they are being put under for and then awakening from a surgery
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Stage I: Analgesia
Stage II: Excitement Stage III: Surgical Anesthesia surgery performed and anesthetic stopped Stage II: Excitement Stage I: Analgesia |
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definition of general anesthetic
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drug which causes analgesia, amnesia, loss of consciousness, inhibition of sensory and autonomic reflexes, and skeletal muscle relaxation
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why is it important that general anesthetics inhibit autonomic reflexes?
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prevents the patient's blood pressure and heart rate from changing when an incision is made
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what is the advantage to quick induction with general anesthetics?
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with fast induction, the patient passes rapidly through the undesirable "excitement" phase (stage II) of anesthesia
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define induction, as it pertains to anesthesia
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rate of onset of anesthesia
(how quickly alveolar partial pressure of an anesthetic equilibrates with inspired partial pressure of the anesthetic) **initially, the inspired partial pressure is much greater than the alveolar partial pressure** |
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define maintenance of anesthesia
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maintaining constant alveolar partial pressure of anesthetic at therapeutic levels
**during maintenance, inspired partial pressure of the anesthetic will be equal to the alveolar partial pressure of that anesthetic** |
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define recovery from anesthesia
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rate of decline of alveolar partial pressure of an anesthetic
**when a surgery is finished and a patient is being weaned from anesthesia, the alveolar partial pressure must decrease from therapeutic levels to zero** |
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define partial pressure
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the partial pressure of a gas in a mixture of gases is the portion of the total pressure (760 mmHg) that is supplied by a particular gas
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why are neuromuscular blocking drugs often used in addition to anesthetics?
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often used to cause flaccidity of muscle, which enables the anesthesiologist to decrease the dose of general anesthetic required
**especially useful when working in highly muscular areas, like the abdominal cavity** |
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what is the main difference between a low-flow anesthetic machine and a high-flow anesthetic machine?
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a low-flow system has a carbon dioxide absorber, whereas the high-flow system doesn't
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blood/gas partition coefficient
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ratio describing distribution of a gas between two phases (gas and blood) at equilibrium; i.e. ratio of gas dissolved in a given volume of solvent to the amount of free gas that would occupy the same volume of space
determines the rate of induction |
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what inactive reservoir must be saturated before anesthetic equilibrium can be achieved?
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proteins in the blood
lipophilicity determines how quickly alveolar partial pressure equilibrates with arterial partial pressure of an anesthetic, b/c lipophilic anesthetics must bind to proteins and fill this reservoir before the partial pressure of the anesthetic in the blood can equilibrate with its partial pressure in the alveoli |
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what are the three main categories of anesthetics classified based on blood solubility?
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soluble - high (double-digit) blood/gas partition coefficient - slow induction rate
intermediate - single-digit blood/gas partition coefficient - intermediate induction rate poorly soluble - blood/gas partition coefficient of about 0.5 - rapid rate of induction |
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what anesthetic is in the intermediate solubility classification of anesthetics?
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isoflurane
blood/gas partition coefficient of 1.4 intermediate rate of induction |
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what anesthetics are in the poorly soluble classification of anesthetics?
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anesthetic (blood/gas partition coefficient)
nitrous oxide (0.47) desflurane (0.45) sevoflurane (0.65) poorly soluble, therefore rate of induction is very rapid |
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what is indicated by a high blood/gas partition coefficient? what does this mean for general anesthetics?
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high lipophilicity
because of high lipophilicity, the general anesthetics will seek out lipophilic portions of the blood (e.g. proteins) |
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what is the active fraction of an inhaled anesthetic?
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the portion of anesthetic that exerts a partial pressure
portion of anesthetic dissolved in the water of plasma after the lipophilic portions of the blood (proteins) have been saturated |
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what is the effect of lipophilicity on rate of induction of general anesthetics?
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high lipophilicity -> saturates proteins (inactive reservoir) -> Part equilibrates with Palv -> slow induction
low lipophilicity -> only small amt goes to lipophilic portions of blood -> Part equilibrates with Palv -> rapid rate of induction |
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what are the stages in the equilibration of the partial pressure of an anesthetic that is inspired with the partial pressure of that anesthetic in the brain?
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1) alveolar partial pressure of an anesthetic equilibrates with inspired partial pressure of the anesthetic
2) arterial partial pressure equilibrates with alveolar partial pressure 3) arterial partial pressure equilibrates with brain partial pressure |
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describe the equilibration of alveolar partial pressure of an anesthetic with the inspired partial pressure of the anesthetic
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the particular anesthetic used plays a large role
loading dose can be used for a few minutes to decrease the time required for this equilibration |
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describe the equilibration of arterial partial pressure of an anesthetic with the alveolar partial pressure of the anesthetic
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takes about ten seconds for the blood in lung capillaries to reach the capillaries of the systemic circulation
this equilibration occurs very quickly |
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describe the equilibration of arterial partial pressure of an anesthetic with the brain partial pressure of the anesthetic
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particular anesthetic used plays little/no role on rime required
this equilibration occurs pretty quickly regardless of which anesthetic is used since all general anesthetics are somewhat lipophilic, they cross the blood-brain barrier readily |
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what is the only way to increase the speed of recovery from a general anesthetic?
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agents with a quick induction have a quick recovery
advantage to a quick recovery is that the patient passes through phase II (excitement phase) quickly |
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minimum alveolar concentration (MAC)
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minimum concentration (partial pressure) of anesthetic necessary to prevent movement in response to surgical skin incision in 50% of patients (measure of potency of inhaled anesthetic)
1.3xMAC is used during surgery to prevent movement in 95% of patients |
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what is the most potent inhaled anesthetic?
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methoxyflurane (1MAC = 0.16% of atmospheric pressure)
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what is the least potent inhaled anesthetic?
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nitrous oxide (fills any empty cavity b/c it is a gas where other anesthetics are volatile liquids)
1MAC = 101% of atmospheric pressure can only go to 80%, therefore nitrous oxide is an incomplete anesthetic |
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how is MAC determined for mixtures of inhaled anesthetics?
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MAC = minimum alveolar concentration
MACs are additive for the different anesthetics used (e.g. 0.5MAC N2O + 0.5MAC halothane = 1.0MAC) |
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what is the advantage of mixing anesthetics?
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reduces the side effects due to each drug
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what is the effect of temperature on minimum alveolar concentration for inhaled general anesthetics?
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at lower temperatures, the MAC is lower (patient is more sensitive to general anesthetics)
at higher temperatures, the MAC is higher |
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what is the effect of age on minimum alveolar concentration for inhaled general anesthetics?
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as a patient gets older, the MAC decreases (elderly patients are more sensitive to general anesthetics than are young patients)
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what is the effect of SNS/CNS altering drugs on the minimum alveolar concentration for inhaled general anesthetics?
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pt with a blood-alcohol content of 0.2% requires a lower dose of general anesthetic
chronic alcoholic without alcohol for a couple days requires a higher dose of general anesthetic patient on CNS-depressing drugs requires lower dose of general anesthetics patient on CNS-stimulating drugs requires higher dose of general anesthetics |
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what is the effect of barometric pressure on minimum alveolar concentration for inhaled general anesthetics?
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decreased barometric pressure results in increased MAC
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what factors have no effect on the minimum alveolar concentration for inhaled general anesthetics?
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1) duration of administration (length of surgery)
2) biotransformation (more drug is required, but MAC remains same) 3) gender 4) blood pressure 5) arterial oxygenation 6) level of ventilation 7) hemoglobin concentration (anemia doesn't affect MAC) |
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what is the Meyer-Overton theory of anesthesia?
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developed in 1900
states that anesthetic dissolves in lipid membrane, causes expansion, and subsequently the reversible inhibition of synaptic transmission changes the properties of the cell membrane rather than using a receptor states that anesthetics increase the affinity of the GABA receptor for GABA and inhibit the excitatory (glutamate) receptors |
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how can the minimum alveolar concentration of an inhaled general anesthetic be predicted?
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MAC x (oil/gas partition coefficient) = 1.3
can fit a logarithmic scale line very well, thus MAC is actually the partial pressure required to generate a particular concentration of anesthetic in a lipophilic medium (i.e. lipid bilayers of CNS) |
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what is the antagonist to general anesthetics?
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since general anesthetics' effects aren't receptor-mediated, there is no antagonist to them
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what is the effect of general anesthetics on the minute ventilation?
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decreases tidal volume, which consequently decreases minute ventilation
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what is the effect of general anesthetics on the respiratory rate?
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increases the respiratory rate
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what is the effect of general anesthetics on the arterial PCO2?
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increases arterial PCO2, leading to undesirable CV effects (changes TPR and CO)
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what is the effect of general anesthetics on the ventilatory response to carbon dioxide?
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with increasing PaCO2, the minute ventilation increases in a linear manner (plot of minute ventilation vs. PaCO2); the effect of general anesthetics is to decrease the slope of this line, so that the increase in minute ventilation is less than that seen with a comparable increase in PaCO2 without general anesthetics
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what is the effect of general anesthetics on the ventilatory response to hypoxemia?
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general anesthetics abolish the ventilatory response to hypoxemia; usually the minute ventilation increases as a result of low PaO2 (curves up after a certain partial pressure), but with general anesthetics the minute ventilation remains constant regardless of how low the PaO2 gets
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what is the only general anesthetic that doesn't increase PaCO2?
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nitrous oxide (N2O)
advantage - can be used in combination with other general anesthetics to give anesthesia without causing the undesirable CV effects (changing TPR and CO) |
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for what reasons can nitrous oxide be used in combination with other general anesthetics?
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1) decrease hypercapnea caused by other GAs
2) improve hypotension caused by other GAs |
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what is the only general anesthetic that doesn't decrease blood pressure?
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nitrous oxide (it can be used in combination with other general anesthetics in order to decrease the hypotensive effects of the other general anesthetics)
all others decrease TPR sevoflurane decreases CO |
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what are the effects of general anesthetics on the CNS? why is this undesirable?
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general anesthetics cause an increase in cerebral blood flow
undesirable b/c intracranial tumors cause increasing pressures within a closed vault (skull) and if more blood is flushed into the skull, intracranial pressure rises to a dangerous level |
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what is the general anesthetic of choice for patients with high intracranial pressure (patients with tumors)?
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isoflurane
b/c it doesn't cause as extensive elevation of intracranial pressure as the rest of the inhaled general anesthetics |
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what is the effect of general anesthetics on the kidneys?
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general anesthetics decrease renal blood flow, but usually this isn't clinically significant because it doesn't cause any pathology
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why is nitrous oxide combined with a narcotic (fentanyl) to be used as a general anesthetic?
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the narcotic doesn't affect blood pressure or cardiac output
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why is anesthetic metabolism important?
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can have toxic effects on the kidneys and liver
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what factors influence the extent of biotransformation of inhaled general anesthetics?
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1) enzyme activity - genetic factors/enzyme inducers may determine an individual's ability to metabolize the compound
2) substrrate availability - poorly soluble anesthetics (low blood/gas partition coefficient) leave little substrate available for metabolism; these anesthetics are exhaled rapidly |
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halothane-associated hepatic dysfunction
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rare dysfunction (1/30,000 pts treated), but is associated with high mortality
profile of affected patient: middle-aged obese female fever then jaundice repeated exposure unknown mechanism - reactive intermediates attach to liver cell membranes and exert toxic effects |
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what patients should not be given halothane?
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a) morbidly obese
b) repeated exposure c) liver disease d) enzyme induction |
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biotransformation of methoxyflurane
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very soluble drug (high oil/gas partition coefficient), so about 50% of the absorbed dose is metabolized
transformation frees up fluoride and increases serum concentration, causing neprotoxicity never use methoxyflurane, but the important thing is that general anesthetics are metabolized and cause problems (e.g. the nephrotoxicity) |
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biotransformation of isoflurane
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chemically and pharmacologically similar to enflurane
metabolism is minimal (about 0.17%) |
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biotransformation of sevoflurane
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though it has a low blood/gas partition coefficient, a surprisingly large amount (3% of dose) is metabolized; this causes significant amounts of fluoride buildup in the blood during long surgeries
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why would you not want to use sevoflurane in long surgeries?
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though it has a very low blood/gas partition coefficient, a surprisingly large amount (3%) is metabolized, which causes significant amounts of fluoride to build up in the blood during long surgeries
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biotransformation of desflurane
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essentially no metabolism (0.02%)
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why are IV anesthetics used, in general?
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used for induction, so that you can skip phase 2 (excitement phase; nightmare)
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what is the most commonly used ultra-short-acting barbiturate as a general anesthetic?
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thiopental
crosses the blood-brain barrier and establishes a brain:plasma equilibrium within 1 minute because of high lipid solubility |
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why are barbiturates (thiopental) ultra-short-acting general anesthetics?
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they rapidly diffuse out of the brain and other highly vascular tissues and are redistributed to muscle, fat, and eventually all body tissues
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thiopental
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ultra-short-acting barbiturate
used as an IV general anesthetic for induction rapid redistribution causes this to be very short acting |
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propofol
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drug of choice as an IV general anesthetic agent; great for inducing anesthesia
smaller doses widely used for sedation in ICU oil at room temperature, supplied as an emulsion more rapid emergence from anesthesia than with thiopental; also characterized by minimal postoperative confusion |
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what are the advantages of propofol over thiopental as IV general anesthetics?
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more rapid emergence from anesthesia with propofol than with thiopental
minimal postoperative confusion associated with propofol |
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etomidate
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IV general anesthetic used to induce anesthesia; also used in combination with succinyl choline for intubation in code situations
increases available GABA receptors, perhaps by displacing an endogenous GABA inhibitor causes minimal respiratory and cardiovascular depression |
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malignant hyperthermia
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dangerous increase in body temperature brought on by the use of anesthetics
- mainly determined by genetic predisposition of the patient - caused by calcium leak from the SR of skeletal muscle causing massive contractions and heat production Tx: dantrolene (stabilizes the SR membrane without interfering with action potentials - acts like a calcium channel blocker) |
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propofol
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drug of choice as an IV general anesthetic agent; great for inducing anesthesia
smaller doses widely used for sedation in ICU oil at room temperature, supplied as an emulsion more rapid emergence from anesthesia than with thiopental; also characterized by minimal postoperative confusion |
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dantrolene
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essentially a calcium-channel blocker, though it doesn't bind to the calcium channels; stabilizes the SR membrane without interfering with action potentials
used as a Tx for malignant hyperthermia |
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what are the advantages of propofol over thiopental as IV general anesthetics?
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more rapid emergence from anesthesia with propofol than with thiopental
minimal postoperative confusion associated with propofol |
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etomidate
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IV general anesthetic used to induce anesthesia; also used in combination with succinyl choline for intubation in code situations
increases available GABA receptors, perhaps by displacing an endogenous GABA inhibitor causes minimal respiratory and cardiovascular depression |
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malignant hyperthermia
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dangerous increase in body temperature brought on by the use of anesthetics
- mainly determined by genetic predisposition of the patient - caused by calcium leak from the SR of skeletal muscle causing massive contractions and heat production Tx: dantrolene (stabilizes the SR membrane without interfering with action potentials - acts like a calcium channel blocker) |
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dantrolene
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essentially a calcium-channel blocker, though it doesn't bind to the calcium channels; stabilizes the SR membrane without interfering with action potentials
used as a Tx for malignant hyperthermia |
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propofol
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drug of choice as an IV general anesthetic agent; great for inducing anesthesia
smaller doses widely used for sedation in ICU oil at room temperature, supplied as an emulsion more rapid emergence from anesthesia than with thiopental; also characterized by minimal postoperative confusion |
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what are the advantages of propofol over thiopental as IV general anesthetics?
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more rapid emergence from anesthesia with propofol than with thiopental
minimal postoperative confusion associated with propofol |
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etomidate
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IV general anesthetic used to induce anesthesia; also used in combination with succinyl choline for intubation in code situations
increases available GABA receptors, perhaps by displacing an endogenous GABA inhibitor causes minimal respiratory and cardiovascular depression |
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malignant hyperthermia
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dangerous increase in body temperature brought on by the use of anesthetics
- mainly determined by genetic predisposition of the patient - caused by calcium leak from the SR of skeletal muscle causing massive contractions and heat production Tx: dantrolene (stabilizes the SR membrane without interfering with action potentials - acts like a calcium channel blocker) |
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propofol
|
drug of choice as an IV general anesthetic agent; great for inducing anesthesia
smaller doses widely used for sedation in ICU oil at room temperature, supplied as an emulsion more rapid emergence from anesthesia than with thiopental; also characterized by minimal postoperative confusion |
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what are the advantages of propofol over thiopental as IV general anesthetics?
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more rapid emergence from anesthesia with propofol than with thiopental
minimal postoperative confusion associated with propofol |
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etomidate
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IV general anesthetic used to induce anesthesia; also used in combination with succinyl choline for intubation in code situations
increases available GABA receptors, perhaps by displacing an endogenous GABA inhibitor causes minimal respiratory and cardiovascular depression |
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dantrolene
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essentially a calcium-channel blocker, though it doesn't bind to the calcium channels; stabilizes the SR membrane without interfering with action potentials
used as a Tx for malignant hyperthermia |
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malignant hyperthermia
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dangerous increase in body temperature brought on by the use of anesthetics
- mainly determined by genetic predisposition of the patient - caused by calcium leak from the SR of skeletal muscle causing massive contractions and heat production Tx: dantrolene (stabilizes the SR membrane without interfering with action potentials - acts like a calcium channel blocker) |
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dantrolene
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essentially a calcium-channel blocker, though it doesn't bind to the calcium channels; stabilizes the SR membrane without interfering with action potentials
used as a Tx for malignant hyperthermia |
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use of opiates with regards to general anesthetics
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used as a premedication for sedation and analgesia
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use of benzodiazepines in regards to general anesthetics
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used as a premedication for their anxiolytic effects
e.g. diazepam, lorazepam additionally, midazolam causes amnesia in 20% of patients |
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usefulness of antimuscarinics in general anesthetics
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e.g. atropine, glycopyrrolate
general anesthetics increase mucous secretions in lungs and causes patients to wake up with a dry mouth - antimuscarinics combat these effects |
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midazolam
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benzodiazepine
useful as a premedication for general anesthetics for anxiolytic effects; also causes amnesia in 20% of patients |
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atropine
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antimuscarinic
useful with general anesthetics to block mucous secretion in the lungs that is caused by the general anesthetics |