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27 Cards in this Set
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- Back
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general anesthetics definition
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general, but reversible depression of CNS function resulting in the loss of response to and perception of all external stimuli
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the ideal general anesthetic would have these characteristics:
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amnesia
analgesis (inhibition of sensation and pain) loss of consciousness (eliminates awareness) skeletal muscle relaxation (allows endotracheal intubation) reduction of ANS reflex activity quick acting and rapidly eliminated no toxic effects- large margin of safety |
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4 stages of analgesia
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1. analgesia
2. excitement (delirium) 3. surgical anesthesia 4. medullary depression skip stage 1 and 2, but do not cross stage 3 or death |
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1. analgesia
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pt is sedated, drowsy, but conscious with analgesia
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2. excitement (delerium)
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pt. has violent behavior, hyperactivity, irregular blood pressure and respirations
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3. surgical anesthesia
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surgery stage, no movement, regular respiration and BP, loss of muscle tone
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4. medullary depression
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loss of respiration and vasomotor control, death
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types of general anesthetics
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intravenous
inhalation (gases and volatile liquid) |
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why are general anesthetics used?
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1. induce loss of consciousness and paralysis
2. induce sedation for outpatient settings and minor surgeries |
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intravenous general anesthetics:
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used to induce anesthesia
high lipid solubility, easily pass BBB have very short onset time but long recovery time organs with higher blood perfusion (brain) receive high amount of anesthetic induce anesthesia for few minutes then redistributs in other tissues |
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intravenous anesthetic agents
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1. benzos
2. ultra short acting barbs 3. etomidate 4. propofol 5. ketamine |
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benzos
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-bind to benzo site on GABA receptor
-midazolam- short acting used as anxiolytic, sedative, induced anesthesia or induces conscious sedation -lorazepam- intermediate acting used as sedative and induce amnesia -diazepam- long acting used as a preop sedative -minimal effect on respiration and cardiac function -benzo antag: flumazenil, useful to treat OD |
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ultra-short acting barb
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thiopental
-binds to Cl channel and potentiates effect of GABA -SE: respiratory depression, CV depression, decrease in BP, reflex tachycardia, hangover, N/V |
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etiomidate
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-enhange the effect of GABA in the Cl channel
-minimal effect on heart and respiration; increases HR, excellent drug in elderly or limited cardiac reserve patients -SE: adrenocortical steriodogenesis suppression, myoclonic muscle movement in 40% of patients, N/V common |
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propofol
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-most commonly used induction agent today
-enhances action of GABA -characterized by rapid onset rapid recovery and enti-emetic effect -SE: cardiac depression, hypotension, impairs baroreflex so it doesn't produce reflex tachycardia |
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ketamine (Special K)
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-NMDA receptor antagonist
-produces (dissociative anesthesia), patient may appear conscious, his eyes are opened but he is unable to respont to sensory stimuli -normal reflexes are maintained -has analgesic effect, can be injected IM -SE: HTN, increased HR and CO, postoperative symptoms: hallucination, excitation, vivid dreams |
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inhalational anesthetics
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-used to maintain anesthesia
-small therapeutic index and no antagonist exist -gas: nitrous oxide (laughing gas) -volatile liquids: isoflurane -long onset time, short recovery time -delivered through inhalation and excreted by expiration |
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uptake and distribution of inhaled anesthetics
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-drug diffuses through the alveoli to the blood then the brain
-partial pressure of the drug is the driving force for drug delivery to the brain -there is always an equilibrium between the partial pressure of the drug between alveoli/blood/brain |
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rate at which a therapeutic concentration of the anesthetic is achieved in the brain depends upon:
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1. primarily on the solubility properties of the anesthetic
2. its concentration in the inspired air 3. the volume of pulmonary ventilation 4. the pulmonary blood flow |
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blood solubility
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-describes the affinity of the gas for a given substance
-blood:gas partition coefficient (I) descrbines how the gas will partition itself between the 2 phases of equilibrium -ex. halothane I=2.3, which means that at equilibrium, the concentration of halothane in the blood will be 2.3 times higher than the concentration in the alveoli -the higher the (I), the higher the uptake of the gas into the blood, thus a slower induction time an agent that is more soluble in blood exerts its effect more slowly |
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anesthetic concentration in the inspired air
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a) increased concentration of anesthetic = faster induction
-increases in the inspired anesthetic concentration increase the rate of induction of anasthesia by increasing the rate of transfer into the blood b)second gas effect = faster induction -moderately soluble anesthetics are often administered in combination with a less soluble agent (e.g. nitrous oxide) to reduce the time required for loss of consciousness and achievement of a surgical depth of anesthesia 3) pulmonary ventilation -increased ventilation (rate and/or depth) = faster induction 4) pulmonary blood flow (CO) -high CO= slower induction |
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how are inhalational anesthetics measured?
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defined by minimum alveolar concentration (MAC)
MAC of 1 is defined as the median concentration that results in immobility in 50% of patients when exposed to a noxious stimulus (surgical incision) |
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Factors that can alter AMC
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a) increase MAC (make pt. less sensitive)
-hyperthermia -drugs that increase CNS catecholamines -chronic ethanol abuse -pregnancy b) decrease MAC (make patient more sensitive) -hypothermia -increased age -acute ethanol intoxication -second gas effect- N2O 40% and 0.5% halothane c) no change in MAC -thyroid gland dysfinction -duration of anesthesia -male or female -height/weight |
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commonly used inhalational anesthetics
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-nitrous oxide (non-halogenated)
-potent inhaled anesthetics: halogenated desfurane sevoflurane isoflurane halothane (hepatic toxicity, no longer used) methoxyflurane- use restricted due to nephrotixicity |
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nitrous oxide
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-nonirritating, sweet-smelling, colorless gas
-very high MAC; not useful for deep anesthesia -used as analgesic at 30-50% -used for conscious sedation -additive effect when used with other inhalational anesthetics -mild increase inc ardiac output, no effect on RR, N/V in high dose (>50%) |
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volatile inhalational anesthetics
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-all are noderate bronchodilator and moderate muscle relaxant
-all are respiratory depressant and cause drop in BP -all trigger the development of malignant hyperthermia |
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sedatives/analgesice adjunct to anesthesia
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a) opiates (analgesia/sedation)
-fentanyl: very frequently used during surgery to suppress patient response to pain stimuli b) a2 adrenergic agonists (analgesia/sedation) -clonidine c) antihistaminic (sedation/anti-emesis) d) muscle relaxant: relax muscles of neck, airway and jaws, facilitate endotracheal intubation -2 groups of muscle relaxant: -depolarizing agents: succinyl choline -non-depolarizing agents: pancuronium |
