General anesthetics- drugs

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Lichtblau 3/12/12

what are characteristics of an ideal inhalation anesthetic?

stable shelf life, compatible w/ existing delivery equipment, inexpensive, NON-explosive and NON-flammable, easily vaporized in ambient conditions, LOW BLOOD SOLUBILITY, POTENT (so only need small amount), no cardiopulmonary depression, NOT IRRITATING to airways (so pt won't fight it), no interaction w/ catecholamines, good muscle relaxant, minimal metabolism, NON toxic to kidneys, liver or gut

in modern inhalation anesthesia what plane do we use?

plane I- lgiht anesthesia supplemented w/ neuromuscular blockers

why do we intubate patients in inhaled anesthesia?

control respiration rate and prevent aspiration

what are some examples of halogenated hydrocarbon inhalation anesthetics?

halothane, isoflurane, methoxyflurane, sevoflurane

what effects to halogenated hydrocarbon inhalation anesthetics have on the CNS?

decrease brain metabolic rate, increase cerebral blood flow, increase intracranial pressure

why do you need to be careful when giving anesthetics to a patient with a history of head trauma?

halogenated hydrocarbon inhalation anesthetics can increase intracranial pressure

what effects do halogenated hydrocarbon inhalation anesthetics have on the cardiovascular system?

decreased myocardial contractility and stroke volume --> lower arterial BP

what halogenated hydrocarbon inhalation anesthetics have the most potent cardiovascular effects? the least?

halothane> isoflurane, desflurane, sevoflurane > nitrous oxide

what do halogenated hydrocarbon inhalation anesthetics do to respiration?

depress it

which halogenated hydrocarbon inhalation anesthetics affect respiration the most? the least?

isoflurane, desflurane, sevoflurane > halothane > nitrous oxide

what do halogenated hydrocarbon inhalation anesthetics do to muscles at high doses?

relax them

malignant hyperthermia can occur with all halogenated hydrocarbon inhalation anesthetics except which one? with which one is it most commonly seen?

except nitrous oxide

msotcommonly seen with halothane

in what form do you find halothane at an ambient temperature?

volatile liquid, usually has a preservative as can breakdown in soda lime (used in anesthesia delivery system to remove CO2)

what are the advantages of halothane?

nonflammable, potent (MAC 0.7- 0.9), rapid induction and recovery, among least expensive volatile anesthetics, doesn't irritate larynx, uterine relaxation

what are the disadvantages of halothane?

inadequate analgesia and muscle relaxation, depressed myocarium and baroreceptor relfexe, SENSITIZES myodarium to catecholamines (increase automaticity), increases cerebral blood flow ad intracranial pressure, respiraotyr depression, potential for hepatic toxicity, malignant hyperthermia, shivering during recovery, porlonged drowsiness for several hrs post recovery

how is halothane eliminated?

60-80% in exhaled breath unchanged
10-20% metabolized in liver

in what form would you find isoflurane at ambient temperature?

volatile liquid that is chemically stable

one of most common inhalation anesthetics

what are the advantages of isoflurane?

nonflammable, potnet (MAC 1.2- 1.6), induction in less than 10 min, doesn't sensitize myocardium to catecholamines, has muscle relazing action, less hepatotoxicity and renal toxicity that halothane

what are the disadvantages of isoflurane?

rarely arrhythmias, pungent odor, potential for malignant hyperthermia

how is isoflurane eliminated?

exhaled breath- less than 0.2% metabolized- may be responsible for lower incidence of heptotoxicity

how would you find desflurane at an ambient temperature?

has a high vapor pressure so can only use w/ specialized temp controlled pressurized vaporizer

what are the advantages of desflurane?

low blood solubility= rapid induction and recovery (good for same day surgery), MAC 7-10 %, little to no heptao or renal toxicity

what are the disadvantages of desflurane?

may increase intracranial pressure but of no consequence unless pt already compromised

how is desflurane eliminated?

exhaled breath, almost no metabolism means no toxicity

what is the newest approved inhalation agent for use?

sevoflurane

how would you find sevoflurane at ambient temperature?

volatile liquid requiring preservative d/t breakdown in lime soda

what are the advantages of sevoflurane?

MAC 2.1- 2.6 so high potency and low blood solubility, almost the perfect inhalation anesthetic, rapd induction and recovery, lneed low percentage of inspired air

what are disadvantages of sevoflurane?

renal toxicity

how is sevoflurane eliminated?

mostly inhaled breath, 3.5- 5% as inorganic fluoride

how would you find nitrous oxide at an ambient temperature?

only inhalation anesthetic that is a gas!
chemically inert

what are the advantages of nitrous oxide?

low blood solubility = rapid onset, little effect overall on CV system, second gas effect, mild to moderate analgesic activity

what are the disadvantages of nitrous oxide?

MAC= 104% so can't use as sole anesthetic agent, no muscle relaxing effect, diffusion hypoxia if rapidly discontinued

what is diffusion hypoxia?

during recover the rapid transfer from blood to alveoli displace air, lack of oxygen uptake = hypoxia

how do you prevent diffusion hypoxia?

slowly taper anesthetic

what are the advantages of injectable anesthetics over inhaled ones?

act faster as reach surgical plane sooner, best suited for induction of anesthesia, useful for short operative procedures

what are the disadvantages of injectable anesthetics over inhaled ones?

recovery from injectables relatively slower as has to be metabolized, poor muscle relaxation, unsuitable as single drug anesthetic for many surgical procedures, need a neuromuscular blocker

how does blood flow relate to drug action?

higher blood flow leads to rapid delivery of drug to site of action

what is responsible for terminating the action of most injectable anesthetics?

redistribution of drugs to tissues w/ greater mass and relatively good perfusion (skeletal muscle)

what tissues are not involved in restribution? why?

adipose or connective tissue, poor perfusion

what are drug doses based on in reference to redistribution? who is this important for?

lean body mass

important for obese patients

for an obese patient will they need more or less of an anesthetic injected? why?

remember dosing is based on a lean body mass instead of total body weight so really need to look at their skeletal muscle percentage- if same give same dose- if less need a lesser dose as won't redistribute as fast and will act longer/have higher concentration (so DONT give them more just because their fat)

with repeated doses of short acting IV anesthetics what happens? why?

duration of activity may become prolonged, redistribution depends on differences in drug conc between blood and non-brain tissues, which becomes smaller w/ repeated dosing so termination of action begins to depend on metabolism and excretion

how are injectable anesthetics excreted

first of all termination of effect is d/t redistribution to skeletal muscle (dense w/ good perfusion), then metabolized and excreted thru kidney/urine

what is pentobarbital?

a short acting barbiturate

what are 2 ultra short acting barbiturates?

thiopental and methohexital

what will barbituatues do to a patient?

loss of consciousness w/o analgesia- respond to painful stimulus still, low doses hyperalgesic, will have no memory of procedure

what do barbiturates do to the cardiovascular system?

minor changes, doesn't increase intracranial pressure, so good cardiostability and good for pts w/ head trauma

what do barbiturates do to the respiratory system?

depress it

when do you see the effects of IV barbiturates?

high lipid solubility leads to rapid distribution to brain and rapid LOC = 10-20 seconds

when will pts recover from barbiturates?

when drug redistributes to the non-brain tissues

thiopental is acidic or basic? why is that important?

highly alkaline so may precipitate out if injected too fast into circulation or wont' work if put another drug that's in an acidic solution for injection in the same line (think meperidine- demerol)

what is the toxicity for anesthetic barbiturates?

anesthetic dose is between 50 & 75% of LD50

what is barbiturates mechanism of action?

facilitates GABA induced CL- entry into neurons, non-selective CNS depression

what are the advantages of thiopental and methohexical?

rapid onset and short action w/ quick recovery, good for short procedures like fracture setting, radiographic, gynecologic and other types of exams

how are thiopental and methohexital given?

only given IV!!

what are the advantages of propofol?

rapid induction (50 sec) and recovery (4-8 min)
anti-emeti action (nausea)

what is propofol given for?

to maintain anesthesia or used for induction as part of balanced anesthesia technique

how must propofol be given?

as an emulsion (inclides soybean oil, glycerin, egg lecithin and NaOH to adjust pH)

how does the price of propofol compare to that of barbituates?

more expensive

what effect of propofol causes it to have seen an increase in abuse in the surgical setting recently?

when awake feel more "clear headed" and not nauseous so use for "power naps"

what are adverse effects of propofol?

injection site pain

what is etomidate used for?

primarily as an induction agent

what are the advantages of etomidate?

little CV depression and only moderately depressed respiration

how must you administer etomidate?

dissolve in propylene glycol for injection, give slowly to prevent venous irritation

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