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
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
which halogenated hydrocarbon inhalation anesthetics affect respiration the most? the least?
isoflurane, desflurane, sevoflurane > halothane > nitrous oxide
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
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 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
how would you find nitrous oxide at an ambient temperature?
only inhalation anesthetic that is a gas!
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
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 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 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
when do you see the effects of IV barbiturates?
high lipid solubility leads to rapid distribution to brain and rapid LOC = 10-20 seconds
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 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
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)
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 the advantages of etomidate?
little CV depression and only moderately depressed respiration