5.6 General Anesthetics Flashcards
(137 cards)
1
Q
Anesthesia
A
partial or complete loss of all sensation w/ or w/o loss of consciousness
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Q
General anestesia
A
reversible loss of all sensation and consciousness
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Q
anestesia is a reversible condition of
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comfort, quiescence and physiological stability in a patient before, during, and after performance of a procedure (usually surgical)
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Q
General anesthesia
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for surgical procedure to render the pt unaware/unresponsive to the painful stimuli
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Q
GA is characterized by
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loss of conciousness, analgesia, amnesia, skeletal muscle relaxation, inhibition of autonomic and sensory reflexes
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analgesia
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perception of pain eliminated
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Q
hypnosis
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unconsciousness
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essential components of GA
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analgesia, hypnosis, depression of spinal motor refexes, muscle relaxation –> these terms together emphasize the role of insensibility and of immobility
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Q
Surgery before anesthesia
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soprifics, Narcotics, marijuana, belladonna and jimson weed, induction of psychological state of anesthesia by mesmerism or hypnosis
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Q
Surgical stress
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evokes HPA axis and sympathetic system
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Q
Tissue damage during surgery induces
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coagulation factors and activates platelets leading to hypercoagulability of blood
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Q
Anesthesia decreases
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the components of surgical stress response
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Q
hallmark of anesthesia
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analgesia, amnesia, muscle relaxation
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Q
anestheisa is associated with
A
dec in systemic BP (due to myocardial depression and direct vasodialation), blunting of baroreceptor control and decreased central sympathetic tone, muscle relaxation (valuable during anesthesia –facilitates endotrachal intubation)
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Q
Pre-anesthetic medication
A
use of drugs prior to anesthesia to make it safer and more pleasant, aim is to relieve apprehension and facilitate smooth induction, to supplement analgesic, amnesic aciton of anesthetics, used of preanestetic can decrease requirment of general anesthetic
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Q
Preanestetics
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benzos, antihitaminics, antiemetics, opiods, atropine
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Q
benzo
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relive anxiety
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Q
antiheistameinics
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prevent allergic reactiosn
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Q
antiemetics
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prevent nausea and vomiting (antipeptic ulcer drugs can also be given)
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opiods
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provide analgesia
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atropine/anticholinergics
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prevent bradycardia and secretion
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Q
balanced anesthesia
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no single drug achieves all of the desired goals of anesthesia, refers to a combination of drugs used to take advantage of individual drug properties while attempting to minimize their adverse effects, effects are additive, improves potency and provides rapid recovery
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other drugs can be administered
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pre, intra, or post operatively to achieve balanced anesthesia, to ensure smooth induction, analgesia, sedation, and smooth recovery. Cater to the individual drug need of the situation.
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Q
Stages of anesthesia
A
4
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stage 1
analgesia
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stage 2
excitement, combative behavir-dangerous state
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stage 3
surgical anesthesia -- further classified into 4 different substages
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stage 4
medullary paralysis -- respiratory and vasomotor control seases
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General anesthetics unique drugs
not usually used for therapeutic or preventive, or diagnostic purposes
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Molecular mechanisms of GA
Gaba-A rec Cl channes, glycine receptors
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GabaA action of GA
facilitate Gaba mediated inhibition at Gaba-Arec sites
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GabaA acting drugs
halothane, propofol, etomidate
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glycine receptor action
activity increased, inhaled anesthetics
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NMDA rec actions
inhibited by Ketamine, N2O
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Mechanisms of Gas
depress synamptic transmission, potentiate, block cation channel, receoptor operated ion channels primary site of action
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potentiation of gaba action
pzds, barbiturate, propofol
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inhibit NMDA rec
Ketamine
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induction
period of time from the onset of administration of the anesthetic to the development of effetive surgical anesthesia, induction of anesthetisa depends on how fast effective concentration of the anesthetic drugs reach the brain, maybe req for breif period then start maintanance drugs
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maintainces
provides sustained surgical anesthesia, after pt is unconcious
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recovery
time from discontinuation of administration of anesthesia until consciousness and protective physiologic reflexes are regained, recovery is the revers of induction and epends on how fast the anesthetic drug diffuses back from the brain, must restore muscle fn before removing endotrachal tube so ask pt to do things so you know pts voluntary muscls are functioning
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two types of anesthetics
intravenous - for induction, inhalational - for mainenance
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if procedure is short
induction drug can be used without a maintainance drug
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intravenous inducing agents
thiopental, methohexital, propofol, etomidate, ketamine
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ketamine
can be used for a brief surgical procedure
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inhalational gas
nitrous oxide (N2O) -- cant be used alone so use it with something -- need to give O2 when you're giving anesthesia!!
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inhalational vaporized liquid
halothane, enflurane, isoflurane, desflurane, sevoflurane, ether
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slower acting durgs as adjunct
benzos and opioids
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benzo andjunct
diazepam, lorazepam, midazolam
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opiods
fentanyl
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IV anesthetics uased for
rapid induction of anesthesia, produce loss of conciousness in one arm-brain ciruculation time (10 to 20s), high lipophilicity, rapid onset of action, reduce the amount of inhalation anesthetic required for maintenance
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recovery from IV anesthetics
maily by redistribution
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Thiopental action
ultra short acting barb, having high libid solubility, also rapid recovery due to rapid redustribution
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Thiopental time
produces unconsiousnes in approx 20 secons
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Thiopental recovery
consciousness regained withing 10-20 min by redistribution to skeletal muslce/adipose
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Thiopental effects
smooth, pleasant, rapid induction and minimal postoperative nausea and vomiting, eliminated slowly from the body and produce hangover (should not be left on his own --bc even after redistribution some amt of the drug enters the brain and dulls his mind)
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thipental properties
not an analgesic and also a weak muscle relaxant, decreases cerebral blood flow, thus no increase in ICT--> can be used in head injury
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thiopental adverse effects
laryngospasm can occur -- atropine may be useful
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Thipental and CVS
produces severe hypotension in hypovolemic pts, dose not sensitize the heart to catecholamines and hence arrhythmia is rare
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Thiopental complication
can percipitate acute intermittent or veriegate porphyria insusceptible individuals --hence contraindicated
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other uses of thipental
rapidly control the seizures since gaba facilitatory and also mimetic
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Methoxital poency
3x more potent than thiopental, quicker and shorter action than thiopental, excitemtn and restlessness during indcution, pain on injection (like propofol)
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most common IV anesthtic
Propofol
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Propofol
most common IV anesthetic (milk of amnesia) , replaced thiopental as the first choice for anesthesia induction and sedation bc it procduces euphoric feeling (subjectivley "feel better") in the pt and does not cause post anesthetic nausea and vomiting, dec intracranial pressure
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propofol timeing
unconcsiousness in 45 s and lasts 15minutes
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Propofol can cause
pain on injection, dose dependent dec in BP and resp depression, baradycardia, (frequent), excitatory effects (muscle twitiching, spontaneous movements, hiccups) noted in a few pts
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Propofol benefits
is an antiemetic so no postoperative nasea and vomiting, used for sedation in intensive care untis, also suited for day care surgery bc residual imparmetn is less marked (not like thiopental with hangover effect)
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Ethomidate
induction anesthetic, lacks analgesic effect, rapid onset and short duration of action (5-10 min) (briefer than thiopental
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Ethomidate advantage
little CVS and resp depression, used for induction of anesthesia in pts with coronary artery disease or cardiovascular dysfn such as shock
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what is more common with Ethomidate
restless rigidity
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Why should repeated injections of Etomidate be avoided
it suppresses the production of steroids form th eadrenal gland
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adverse effects of Etomidate
postoperative nasea and vomiting, also causes unpredictable and often sever myoclonus during induction
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Ketamine
a short-acting, non barbituarate anesthetic
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Ketamine induces
dissociative anesthsia by blocking NMDA receptors ---an effect which pts feel dissociated form their surrouding; also produces analgesia and amnesia, with or without loss of consciousness
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Inhalational anesthetics
are gases or vapors that diffuse rapidly across pulmonary alveoli and tissue barriers
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advantages of Inhalational anesthetis
control the depth of anesthesia
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Inhalational metabolism and excretion
metabolism is very minimal and is excreted by exhalation -- what goes incomes out
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Inhalation anesthetics
depth of anesthesia depends upon concnetration of anestehtics in the CNS
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effectiv concentration of inhalation anesthetics
the rate at chich effective concentration achived in barin (induction) depends upon PK parameters of anesthetics, to achieve effective concentration in the CNS anesthetics requre to be transferred from alveoli to blood and from blood to brain
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characteristics of inhalational anesthetics which goveren anesthesia are
solublility in the blood (blood;gaspartition) (soluble form does not produce anesthesia, gas from enters the brain, so lower the blood:gas, the more rapid is induction, sloubility in fat (oil:gas partition) (hihger solubility in fat high potency
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solubiity in blood indicates
rapidity of onset
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solubitiy in fate indicates
potency -- MAC will be less --less amt of the drug will be responsible to mobility
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blood gas coeff
measure of solubility in the blood, determins the rate of induction and reovery of ihalational anesthetics, lower the blood gas coeff, fater the induction and recovery--NO (.47--->but blood gas is low so faster but oil gas ratio is low so potency is very low, meaning lipid oil gas coeff is very low) --MAC is very high ---only few molecules are required to raise its partial pressure in gth blood
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higher blood gas coeff
higher the coeff, slower induction and recovery (Halothane) --more molecules soluble in blood, hence slowly raises its partial pressure tension and onset of action
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NO produces
rapid action bic low blood gas coeff so rapid ly attains pp in gaseous form
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halothane produces
slow action bc high blood gas coeff
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rate of onset and recovery depend on
blood:gas ratio
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the more soluble the anesthetic in the blood
the slower the anesthesia
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high bood gas ratio
slow onset, slow recovery
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low blood gas ratio
fast onset, fast recovery
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higher oilgas coef
higer lipid solubility and potency will bi higher
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higher the lipid solubility
higher the potnecy eg. Halothane
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MAC
minium alveolar concentration (median alveolar concentration) --lowest conc of the anesthtic in pulmonary alveoli (% of the inspired air) needed to produce the immobility in response to painful stimuli (surgical) stimulus in 50% individuals --> ED50 for anesthetic agent
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MAC is a valid measure of
potency of inhalational anesthetics
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the more lipid soluble the anesthetic
the lower the MAC and greater the potency
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MAC values are
additive (lower in the presence of opiods or sedative-hypnotics---so requirement of the inhalational anesthetic will be less) ; also are lower in elderly--so will also requrie less of the drug to produce anesthesia
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concentration response curve
most inhalational anesthetics have a steep con-response curve.
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increasing conc by 1/3 MAC
makes almost all individuals immobile and 2-4 MAC is often lethal, so its not good to go above the MAC value
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relationship of oilgas and MAC
inverse
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relationship of oilgas and potency
direct
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relationship of MAC and potency
inverse
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nonhalogenated gas
nitrous oxide
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halogenated hydrocarbons
halothane, enflurane, isoflurane, desflurane, sevoflurane, methoxyflurane
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what drug produces nephrotoxicity
methoxyflurane
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what is the safest inhalational anesthetic
Nitrous oxide, no effect on respriation and heart, non toxic to liver, kidney and brain
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Nitrous oxide metabolism
does not occur and quickly removed form the body by lungs. Used as a carrer and adjuvant to other anesthetics
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NO mixture
70% N2O + 25-30% O2 + 0.2-2.0% another potent anesthetic _ employed for most surgical procedures
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Nitrous oxide effeects
weak anesthetic (surgical anesthesia cannot be produced on its own), good analgesic, but poor muscle relaxant (often neuromuscular blockers are required)
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NO and Second gas effect
N2O can concentrate the halogenated anesthetics in the alveoli when they are concoamitany adminstrered bc of its fast uptake from the alveolar gas, creating a vacuum space so the other drug is sucked in
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NO and Diffusion hypoxia
when flow of N2O is turend off at the ned of anesthesia, then its concentration int eh alveoli will be lower than in the blood. Consequently N2O floods in from the blood and alveolar gas are diluted with N2o, making pt breathe hypoxic mixture. To overcome this 100% oxygen should be adminsitered to patent unto N2O is washed out.
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NO can cause
pneumothroax and megaloblastic anemia
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NO with O2
has been used for dental and obstetric analgesia
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Halothane effects
potent anesthetic but weak analgesic, inductionis pleasant
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Halothan is also
vagomimetic and can cause bradycardia, produces dose dependent hypotension (to counter excessive hypotension during halothane anesthesia, a direct acting vasoconstricor phenylephrine is given)
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Halothane causes
direct depression of myocardial contractility by reducing intracellular Ca concentration, CO is reduced with deepening anesthesia, sensitizes heart to catecholamines
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what drug is preferred in asthmatics
Halothane, dialates bronchus
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halothane relaxes
skeltal and uterine musle and can be used in obstetrics when uterine relaxation is indicated
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halothane adverse effects
Halothane Hepatitis, Malignant hyperthermia (with all halogenated hydrocarbon anesthetics and musle relaxants succinylcholine---withdraw anestheitc mixtuer and give dantrolene)
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Halothane metabolism
metabolisme significantly (30%) to bromide, trifluoroacetate--responsible for rare heaptotoxicity
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Enflurane difference from halothane
less potent than halothane, but produces rapid induction and recovery, does not sensitize the heart to catecholamines (less chance of arrhythmias), greater potentiation of muscle relaxant, due to a more potent "curare-like" effect
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contraindications of enflurane
seizures (CNS excitation) occur at deeper levels so contraindicated in epileptics; caution in renal failure due to fluoride metabolite, pungent and may result in breath holding or couging and is less accepted by children
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Isoflurane
produces more rapid induction and recovery than halothane, widely used, less likeley than halothane to sensitize the heart to catecholamines or cause arrhythmias, dialates coronary vasculature, increase coronary blood flow and increase oxygen supply to heart - hence beneficial in pts with IHD (ischemic heart disease) ( safe in myocardial ischemia)
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Isoflurane effects
does not provoke seizures, hence preferred in neurosurgery, produces concentration dependent hypotension due to peripheral vasodialation, skeletal muscle relaxation is similar to enflurane, negligible metabolism hence less organ toxicity, postanesthetic nausea and vomiting is low
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Desflurane
induction and recovery very very fast (faster than isoflurane) hence preferred for outpt surgical procedures, less potent than Isoflurane, delivered through special vaporizer (due to low volatility), short-lived postanesthetic cognitive and motor impairment, irritates the air passage (pungent) -- coughing, laryngospasm, and excessive secretion
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Desflurane similarites to isoflurane
degree of respiratory depression, musle relaxation, vasodialation and fall in BP, as well as maintained cardiac contractility and coronary circulation are like Isoflurane, lack of seizure provoking potential or arrhythmogenicity and absence of liver as well as kidney toxicity are similar to isoflurane
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Sevoflurane
fast induction and recovery, absence of pungency and airway irritancy, makes it pleasant and acceptable in pediatric pts, causes bronchodialation, useful for pts with respiratory difficulties, metabolized by liver releaseing fluoride ions, thus like enflurane, raises concerns about nephrotoxicity, inaddition it is very unstable compound, degrades to a nephrotoxic compound
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Neuroleptanalgesia/neuroleptanesthesia
characterized by analgesia, general quiexcnce, psychic indifference and intense analgesia without total unconsciousness, not commonly used, usually reserved where inhalational and or other parenteral anesthetics are relativley contraindicated
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fentanyl (opiods)
short acting
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droperidol
long acting neuroleptic
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neuroleptanalgesia causes
drowsiness but respons to commands, respiratory depression and extra pyramidal s/s seen, used for endoscopies, angiographies and minor operations
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Benzodizepiens as adjucnts
used for anxiolysis, amnesia, and sedation prior to induction of anesthesia, most frequenly used in perioperative period is midazolam (preferred), diazepam and lorazepam
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Analgesics
analgesics are administered with general anesthetics to reduce anesthetic requirment and minimize hemodynamic chanes produced by painful stimulation, opiods are commonly used for these purposes,
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major perenteral opiods given during perioperative period are
fentanyl (most common), sufentanil, alfentanil, remifentanil, meperidine and morphine
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neuromuscular blocking agens
purpose is to relax muscles of the jaw, neck, and airway and thereby facilityate lanryngoscopy and endotrachal intubation, during the induction of anesthesia
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exampls of neuromuscular blockers
pancuronium (non-depolarizing muslce relaxant), Succinylcholine (depolarizing muslce relaxant)
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Properties of ideal gas for the pt
pleasant non irritating, non flammable, should not cause nasea/vomiting, induction and recovery should be fast with no after-effect
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Properties of ideal gas for the surgeon
provide adequeate analgesia, immobility and muscle relaxation
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Properties of ideal gas for the anesthetist
administration should be easy, controllable and veratile, should have wide margin of safety, should not affect ehart, liver, and other organs, rapid adjustment in depth should be possible, should be cheap, stable and easily stored, should not react with rubber tubing or soda lime
