What is general anesthesia?
REVERSIBLE depression of the CNS function resulting in the loss of response to and perception of all external stimuli
What are the 5 components of the anesthetic states?
loss of consciousness
inhibition of sensory and automonic reflexes
skeletal muscle relaxation
what do you use for minor procedures? Why?
oral or parenteral may be used with local anesthetics
provide analgesia but patient is somewhat alert
What is used for more extensive surgical procedures?
preop drugs, IV induction, maintenance with combo of IV and inhaled anesthetics
What are the 4 stages of general anesthesia? What were they observed with?
3. surgical anesthesia
4. medullary paralysis
What is the excitement phase?
delirious, amnesia, BP rises, respiration irregular, RR increased.
Vomiting avoided by IV
What is surgical anesthesia?
skeletal muscle relaxation and regular respiration
eye reflexes progressively diminished and pupils fixed
What is medullary paralysis
severe depression of medullary respiratory and CV centers. DEATH can occur.
What does IV anesthetics reduce? 4 examples?
Stage 2 phase
barbs (thiopental), propofol, ketamine, benzos (midazolam)
What kind of onset do IV have? What about awakening? What determines duration of action?
redistribution ( vessel rich areas are more easily affected)
What the two major groups of inhaled? Name the examples
volatile agents -- halothane, isoflurane, sevoflurane, enflurane, desflurane,
anesthetic gases - nitrous oxide (N20)
How are inhaled anesthetics taken up and distributed?
through partial pressures of anesthetic gases that moves the it into the alveolar space into the blood into the brain.
move through PP GRADIENTS.
steady state is achieved when alveolar PP is equal to brain PP
what does the time of recovery depend on? Which ones are eliminated faster?
the rate of elimination of the anesthetics from the brain.
insoluble in blood are eliminated faster ( like n20)
MOA of inhaled anesthetics
halogenated inhaled agents stimulate GABAa receptors ( cl channels)
N20 inhibits NMDA receptors (glutamate gated channels)
Which regions are important sites of anesthetic actions?
CNS regions such as reticular activating system and cortex
Where do the inhaled forms act cellularly? IV forms? what do they do?
inhaled- inhibit excitatory and enhance inhibitory
IV - -acts at postsynaptic neurons; enhance inhibitory transmission
What are the sites of actions of for these anesthetics? (4)
GABAa receptors, NMDA receptors, K channels that set resting potential, Synaptic release machinery (preventing the vessel from releasing)
What are the effects of anesthesia on the CV system?
Decreased BP due to direct vasodilation
reduced cardiac output and decreased vascular resistance
What the effecst on respiratory effects?
respiratory depression, gag reflex lost, stimulus to cough is blunted, lower esophageal sphincter tone is reduced.
What effects on kidneys? What does halothane cause?
decreased renal blood flow and GFR
hepatotoxicity due to toxic metabolites
Why do surgery patients develop hypothermia?
anesthetics generally lower core temperature set point (so the protective vasoconstriction does not occur to defend against heat loss)
What is a major problem post op? Why?
anesthetics act on the chemoreceptor trigger zone and vomiting center of the brainstem.
modulated by 5HT, Histamine, Ach and DA
What is scopolamine used for?
anticholinergic used to prevent bradycardia and bronchial fluid secretion
How do local anesthetics work?
Block nerve conduction which produces a transient and reversible loss of sensation in a localized area of the body without loss of consciousness
What are the ester locals? Amide?
esters -- cocaine, procaine, tetracaine, benzocaine
What does absorption of a local depend on? What can you add to prolong it?
local blood flow
How are esters metabolized? amides?
esters hydrolyzed in plasma by pseodocholinesterase
amides metabolized in the liver by p450s
What is the deal with pH and locals?
Locals are weak bases.
Must be uncharged to cross the plasma membrane to enter cell to work.
at pH 7.4 -- it is mostly BH+
MOA of locals?
block voltage gated Na channels from the inside...so much be uncharged to get across the plasma membrane.
What else happens with MOA of locals
Increase threshold for excitation with no change in resting potential.
decrease rate of rise of action potential
slow down impulse conduction, the ability to generate an action potential is lost
When are locals less effective ? Why?
when injected into infected tissues
because pH of infected tissue is usually less than 7.4 therefore a smaller percentage of local anesthetic is in the unionized form and unable to cross the membrane
what is the DOC for short acting? Intermediate? Long? which do you add the vasoconstrictor to?
the short and intermediate to prolong action