Term
| when was the first suggestion that N2O could produce general anesthesia? |
|
Definition
| ~1800. it was tried first in 1845 and then successfully in 1846. |
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Term
| what are the inhalation anesthetics? |
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Definition
| *gas: N20 (nitrous oxide/ether) and *volatile liquids: desflurane, enflurane, halothane, isoflurane, methoxyflurane, and sevoflurane |
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Term
| what are the IV anesthetics? |
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Definition
| *ultrashort acting barbiturates: methohexital, thiamylal, and thiopental. *nonbarbiturates: etomidate and propofol. *dissociative agent: ketamine and phencyclidine. *neuroleptanalgesia: droperidol/fentanyl combo. |
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Term
| what characterizes the the therapeutic index for general anesthetics? |
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Definition
| it is low. circulatory arrest dose/general anesthetic dose = 3/1 |
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Term
| what are the stages of anesthesia? |
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Definition
| 1) analgesia 2) delirium 3) surgical anesthesia 4) medullary anesthesia |
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Term
| what characterizes stage I of anesthesia? |
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Definition
| analgesia, which begins w/administration of the anesthetic: depression of signal transmission in the RAS (general sensory) and dorsal horn cells (pain). |
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Term
| what characterizes stage II of anesthesia? |
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Definition
| delirium, which begins w/a loss of consciousness. depression of the cortex results in less inhibition of subcortical areas: disinhibition. this then can lead to hyperreflexia (violent muscular contractions), irregular respiration (apnea alternating w/hyperapnea [problematic w/inhalational anesthesia]), and vomiting (aspiration into the respiratory tract, can cause asphyxiation and postop pneumonia). |
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Term
| what are stage I and II of anesthesia referred to as? |
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Definition
| the induction period, in which the goal is to get to stage III as quickly as possible. |
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Term
| what is stage III of anesthesia? |
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Definition
| surgical anesthesia, which begins w/muscular relaxation and a return to a regular but lower respiratory rate and BP. there is a greater depression of the RAS and spinal cord. |
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Term
| what is stage IV of anesthesia? |
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Definition
| medullary paralysis, which begins w/ cessation of spontaneous respiration, depression of the pons and medulla, and ends w/circulatory failure. |
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Term
| what characterizes uptake and distribution of general anesthetics? how does perfusion compare w/lipid content? |
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Definition
| the objective is to get the pt from conscious to unconscious as rapidly and safely as possible. the perfusion rate is highest in the brain, then muscle, then adipose while lipid content is highest in the adipose, brain and then muscle. |
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Term
| what is the loop bypassed in parenteral anesthesia which is present w/inhalation? |
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Definition
| general anesthesia <-> inspired air <-> lungs <-> blood <-> brain/muscle/adipose |
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Term
| what is the quickest way to achieve a maximum blood level w/general anesthesia? |
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Definition
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Term
| what factors influence the transfer of inhalational GA's (general anesthetics)? |
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Definition
| solubility (blood/gas partition coefficient means GA is more soluble in blood - *if high [NO2] it will move into tissues from blood slowly/if low [halothane] it will rapidly leave the blood for tissues), anesthetic concentration of inspired air (higher concentration = higher rate of transfer) and pulmonary ventilation (faster breaths and/or deeper breaths = faster transfer). |
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Term
| what characterizes elimination of general anesthetics? |
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Definition
| in general, recovery is slower than induction b/c these lipid soluble compounds are stored in fat. expired air is the major route of elimination for inhalational GA's (higher B/G P = longer recovery time). biotransformation is not a major factor. as duration of administration of GA increases, tissue stores increase and recovery takes longer. |
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Term
| what is anesthetic potency determined by? |
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Definition
| blood level and minimum alveolar concentration. MAC (only for inhalational GA) is a unit which refers to the *concentration of the drug in the alveolar space where 50% of patients do not feel the initial surgical incision and there is a very steep dose-response curve: 95% of pts do not feel incision at 1.1 MAC. |
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Term
| why is the mechanism of GA likely not related to a specific receptor? |
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Definition
| b/c drugs w/very different molecules all will still produce general anesthesia. |
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Term
| what is the lipid solubility (myer-overton) GA theory? |
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Definition
| this explains of access of GA to brain tissue but is not related to mechanism of action. no longer accepted. |
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Term
| what is the interaction w/lipid component of bran cell membrane GA theory? |
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Definition
| GA's interact with lipid molecules of cell membrane and shift the membrane to a disordered state = decreased Ca+/Na+ influx (hyperpolarization/decreased release of excitatory NTs). no longer accepted (one GA molecule interacting with one [or even two] lipid molecules is not sufficient to cause the shift). |
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Term
| what is the interaction w/protein component of bran cell membrane GA theory? |
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Definition
| in the same 5000 A^2 area of brain cell membrane is 1 protein molecule. therefore, one GA molecule could bind to this protein molecule & inactivate it; could interfere with operation of an ion channel. most likely one to be inactivated is the K+ channel = an increase in K+ efflux and hyperpolarization. this is the current theory for GA MOA. |
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Term
| do GAs interact w/ the GABA-A receptor? |
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Definition
| GAs may enhance the activity of the GABA-A receptor = increased influx of Cl- = hyperpolarization. |
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Term
| what are 4 examples of pre-anesthetic medication and the reasoning for their used? |
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Definition
| relief of anxiety (sed/hyp/BZDs will also enhance GA effect), decreased secretions (atropine > scopolamine), counteraction of bradycardia (atropone > scopalamine), and elevation of gastric pH (cimetidine, decreases lung scarring if vomiting occurs). |
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Term
| what are the objectives of general anesthesia? how are they met? |
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Definition
| rapid elimination of consciousness, skeletal muscle relaxation, and analgesia. since no single currently available GA can accomplish all of these objectives, general surgery is usually performed using two or more GA's and one or more adjunctive agents ('balanced anesthesia') including: an induction agent (rapid-acting GA), GA, and anesthetic adjuncts (skeletal muscle relaxants/opioids) |
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Term
| what are problems w/biotransformed GAs? |
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Definition
| pre-existing enzyme induction and obesity |
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Term
| is NO2 (inhalation anesthetic) flammable or explosive? |
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Definition
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Term
| what is the effect of NO2 at 20% (80% O2)? (*know this*) |
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Definition
| provides analgesia = morphine and drop in beta-endorphin levels. |
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Term
| what is the effect of NO2 at 50% (50% O2)? (*know this*) |
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Definition
| this is used in dental procedures, no significant respiratory depression. |
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Term
| what is the effect of NO2 at 65% (35% O2)? (*know this*) |
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Definition
| this is the highest concentration which will still provide adequate oxygenation (no hypoxia) |
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Term
| what is the effect of NO2 at 80% (20% O2)? (*know this*) |
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Definition
| most pts are unconscious (stage II). if pts have sickle cell they may go into a crisis at this level. (100% NO2 will still not get pts to stage III). |
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Term
| what are the uses for NO2? |
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Definition
| analgesic (dentistry, acute MI, first stage of labor) and induction of general anesthesia. |
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Term
| what are advantages for NO2? |
|
Definition
|
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Term
| what are disadvantages for NO2? |
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Definition
| not potent, inadequate skeletal muscle relaxation, and dreams of sexual assault (at > 50% conc) |
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Term
| what characterizes acute NO2 toxicity? |
|
Definition
| fall = bone fracture and positional asphyxia |
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Term
| what characterizes chronic NO2 toxicity? |
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Definition
| loss of balance/ataxia, leg weakness, peripheral neuropathy and impotence |
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Term
| what characterizes halothane (volatile liquid)? |
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Definition
| this is rarely used, nonexplosive and nonflammable |
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Term
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Definition
| 1 MAC at .75% conc (high O2 to pt), B/G PC = 2.4 |
|
|
Term
| how much of halothane is biotransformed? |
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Definition
|
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Term
| what are the advantages of halothane? |
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Definition
| nonexplosive, nonflammable, smooth/relatively rapid induction, bronchodilation, and relatively low incidence of toxicity |
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Term
| what are the disadvantages of halothane? |
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Definition
| poor analgesia, poor muscle relaxation, sensitization of the myocardium to catecholamines (any halogenated hydrocarbon can produce card. arrhythmias), hepatitis (not dose-related, possibly allergic, rare but fatal rxn can occur on repeated exposure), and (possibly severe) hypotension (decreased myocardial contractility [decreased entrance and interaction of Ca++ intracellularly] and decreased compensatory tachycardia) |
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Term
| what characterizes the potency of methoxyflurane? |
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Definition
| this is the most potent GA; 1 MAC = 0.16% (maintenance at 0.2 - 0.8%). B/G PC = 12; slow induction (20-30 minutes if used alone). provides more skeletal relaxation, more analgesia and less myocardial sensitization than halothane. |
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Term
| what characterizes the biotransformation of methoxyflurane? |
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Definition
| methoxyflurane is biotransformed 50-70% |
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Term
| what ADRs are associated w/methoxyflurane? |
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Definition
| it can result in flouride toxicity (>50 umol/L serum) which can remain elevated for days. the renal system may be damaged and Fl- diabetes insipidus may be incurred. |
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Term
| what characterizes enflurane? |
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Definition
| this volatile liquid has 1 MAC of 1.68% and a B/G PC of 1.9 (moderately fast induction). provides more skeletal relaxation, more analgesia and less myocardial sensitization than halothane. fluoride toxicity possible; less likely than with methoxyflurane. seizures may occur - but more likely if pre-existing condition. |
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Term
| what characterizes isoflurane? |
|
Definition
| 1 MAC = 1.4%, B/G PC = 1.4. more respiratory irritation on induction than halothane. very limited biotransformation, about .17%. |
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Term
| what characterizes desflurane? |
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Definition
| 1 MAC = 1.4%, B/G PC = .42. biotransformation: .02%. induction of general anesthesia within 2 - 4 minutes but NOT recommended for this purpose due to high incidence of respiratory tract irritation (e.g., laryngospasm, coughing, increased secretions, breathholding, apnea) |
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Term
| what characterizes sevoflurane? |
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Definition
| low blood/gas solubility. no significant odor (good for peds). biotransformed into 2 metabolites: F- (rapidly eliminated b/c parent molecule rapidly cleared - less nephrotox than methoxyflurane) and HFIP (rapidly glucuronidated, low toxic potential) |
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Term
| what are the more common volatile liquid GAs? |
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Definition
| isoflurane, desflurane, and sevoflurane are the more common volatile liquid GA |
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Term
| what characterizes thiopental (ultrashort-acting barbiturate)? |
|
Definition
| this is administered IV or infusion, anesthesia occurs w/in seconds, primary site of action: RAS. emergence from GA is rapid due to redistribution from brain to other tissues *not biotransformation (only about 15% per hour) but may be slow if IV infusion is prolonged. thiopental is stored in adipose tissue and slowly released. |
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|
Term
|
Definition
| induction of GA and as the sole GA for short procedures w/o significant pain. |
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Term
| what are the advantages of thiopental? |
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Definition
| easy to administer, rapid and pleasant induction |
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|
Term
| what are the disadvantages of thiopental? |
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Definition
| lack of moment-moment control, poor analgesia (may cause hyperalgesia), powerful respiratory depressant, and poor skeletal muscle relaxation |
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Term
| what are contraindications w/thiopental? |
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Definition
| pts w/porphyria may experience n/v, paralysis, or death. |
|
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Term
| what characterizes etomidate (nonbarbiturate)? |
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Definition
| this rapid-acting hypnotic has high lipid solubility and wide distribution, but is *not an analgesic. it has minimal effects on HR, CO, and peripheral circulation. etomidate is rapidly metabolized in the liver and primarily excreted in the kidneys. |
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Term
| what uses are associated w/etomidate? |
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Definition
| *induction of GA (onset in 1 min, effects persist 3-5 min), supplemental anesthesia during short operative procedures, and prolonged sedation of critically ill pts. |
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Term
| what ADRs are associated w/etomidate? |
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Definition
| transient venous pain on injection, myoclonic skeletal muscle movements after injection, hypotension/tachycardia/arrhythmias, hyperventilation/transient apnea/laryngospasm/hiccups, and post op n/v. |
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Term
| what characterizes propofol (nonbarbiturate)? |
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Definition
| propofol is prepared as a lipid/water emulsion which has wide and rapid distribution to highly perfused tissues (brain, heart, lungs, liver). hypnosis w/in 40 sec of IV administration and anesthesia w/in 1-3 min. there is some degree of analgetic activity. |
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Term
| what is propofol used for? |
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Definition
| continuous sedation in pts who are intubated or who are on mechanical ventilation (ICU), induction of general anesthesia and maintenance of general anesthesia (in balanced anesthesia). |
|
|
Term
| what is the advantage for propofol? |
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Definition
propofol is extensively metabolized into inactive metabolites (primarily
glucuronide) allowing rapid recovery from sedation or anesthesia. elimination t1/2: 300-700 min. pts are usually oriented and respond to verbal commands approx. 8 min. after infusion terminated. |
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Term
| what ADRs are associated w/propofol? |
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Definition
| pain at the injection site (rash/pruritus), clonic/myoclonic movements, seizures, rigidity, thrashing, confusion, delirium, hallucinations, hypersalivation, bronchospasm, cough, hyperventilation, green urine and urinary retention. |
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Term
| what are cautions for propofol? |
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Definition
| caution in pts w/increased intracranial pressure, not recommended for delivery (neonatal depression may occur), and some fatalities have been reported in pediatric pts being treated in the ICU for respiratory tract infections at high doses. |
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Term
| what characterizes phencyclidine (dissociative agent)? |
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Definition
| aka PCP, this has been withdrawn from human use due to hallucinations during emergence |
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|
Term
| what characterizes ketamine (dissociative agent)? |
|
Definition
| related to PCP, this NMDA antagonist produces "dissociative amnesia" where pts exhibit catatonia, analgesia, and amnesia (eyes open, appear in a trance, unresponsive to pain/stimuli) due to action in the cerebral cortex and limbic system (occurs w/in 15 sec). |
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Term
| what is the duration of the different effects due to ketamine? |
|
Definition
| unconsciousness: 10-15 min, analgesia: ~ 40 min, amnesia: 60-120 min |
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|
Term
| what are the advantages w/ketamine? |
|
Definition
| strong analgesia, no significant respiratory depression, support of the CV (increased HR/BP), and reduced risk of psych ADRs (compared to PCP). |
|
|
Term
| what are the disadvantages w/ketamine? |
|
Definition
| prolonged retention in the body (stored in adipose tissue, traces appear in urine for weeks), psych ADRs upon emergence (nightmares, hallucinations, delirium, schizoid rxns - more common in 30 y/o+ pts, reduce w/conferring, diazepam and avoidance of tactile/verbal stimulation during emergence), and flashbacks (memory phenomenon - not ketamine retention) |
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|
Term
| what are the uses of ketamine? |
|
Definition
| emergency sx, outpt procedure which requires GA, changes in burn dressings, and dx procedures in children |
|
|
Term
| what drugs interact w/GA agents? |
|
Definition
| *tetracyclines: increased risk of nephrotoxicity w/methyoxyflurane. *bacitracin, aminoglycosides, and polymixins: additive skeletal muscle paralysis w/neuromuscular blocking agents (non-depolarizing). *CNS depressants: acute - increased effect, chronic - possible increased effect at time of sx or tolerance. cigarette smokers: may require increased dose of GA due to enzyme induction. |
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|
Term
| what is neuroleptanalgesia? |
|
Definition
| combination of an antipsychotic and opioid which allows: reduced initiative/emotions, some slowness in stimuli response, no effect on intelligence, no effect on coordination. droperidol+fentanyl is given for this as slow IV infusion for minor sx, dx procedures and changing of burn dressings. |
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