general anesthesia Flashcards
mechanism of action of general anesthesia
1- potentiate GABA receptors (inhibitory brain receptors)
2- Inhibiting NMDA receptors (excitatory glutamate receptors)
what happens when u potentiate GABA (A) receptors
increase CL influx -> hyperpolarization -> inhibition of CNS
what happens when u potentiate GABA (B) receptors
decrease Ca influx -> inhibition of CNS
stages of anesthesia
stage 1: stage of analgesia
stage 2: stage of delirium or excitement
stage 3: stage of surgical anesthesia
stage 4: stage of medullary paralysis
stage 1
due to inhibition of sensory transmission -> between the spinal cord and thalamus -> less pain awareness & no loss of consciousness
stage 2
irregular respiratory rate, increase in blood pressure, rapid pulse and mydriasis
Decrease delirium by benzodiazepine
stage 3
regular respiratory and heart rate, normal BP, loss of eye reflexes & muscle relaxation, surgery starts here
stage 4
toxic aesthetics -> respiratory failure & circulatory collapse -> death
Properties of good GA
safe nontoxic to liver n kidney
non explosive n non inflammable
inert (no drug interactions)
rapid n pleasant induction
does not decrease respiratory or cardiovascular centers
has muscle relaxant effecr
night before operation
anxiolytic or sedative to alleviate stress anxiety fear from operation and get good sleep DIAZEPAM
one hour before operation
decrease salivation & protect from bradycardia ATROPINE IM
after induction
short acting neuromuscular blocker to facilitate intubation SUCCINYLCHOLINE
POST OP
MORPHINE IM for pain
antihistaminic + antiemetic drugs
process of GA
1- induction = IV ANESTHESIA
2- maintenance= INHALED ANESTHESIA
3- recovery
classification of GA
1- inhaled anesthesia: gases (nitrous oxide) & halogenated hydrocarbons (halothane, isoflurane, sevoflurane)
2- intravenous agents: barbiturates (thiopental), BZ (midazolam), opioids (fentanyl), others (ketamine, propofol)
Halothane advantages
INHALED
bronchodilator effect =for asthma patients
Halothane disadvantages
1- bradycardia due to vagal stimulation or arrhythmia due to heart sensitization of heart to circulating catecholamines
2- no muscle relaxant effect (curare must be used with it)
3- uterus relaxation & decrease response to oxytocin = not for delivery
4- hepatotoxic= not for liver diseases or repeated surgeries
enflurane & isoflurane
INHALED
same as halothane but strong skeletal muscle relaxant effect & less sensitization of heart = fewer arrhytmias
not for kidney failure patients
methoxyflurane
MOST POTENT (cz of its high solubility in lipids)
INHALED
in labor (doesnt relax uterus)
can be nephrotoxic
nitrous oxide
INHALED
safest
fast pleasant induction with laughing and euphoria
no action on cvs or uterus
no sensitization of heart
used in dentistry & labour
MAC
minimal alveolar concentration
as mac decreases of GA -> more potent
halothane 0.77
n2o=101
Ultra short acting barbiturates
IV
THIOPENTAL
very rapid induction (rapid onset of action = high lipid solubility)
short acting = rapid redistribution from brain
barbiturates disadvantages
1- they can pass placenta (fetotoxic) -> not for delivery
2- hypothermia, postop shivering (cz of inhibition of heat regulatory center)
3- cause dose dependent depression of respiration (not for asthma)
ketamine
IV
antagonist of glutamic acid -> block excitatory action of NMDA
dissociative anesthesia
no hypotension or bronchoconstriction
minor operations (esp kids)
not for pregnancy (oxytocin effect)
disadvantages: hallucination + vivid dreams -> decreased by diazepam -> contraindicated in psycho patients
propofol
IV
induce anesthesia rapidly
maintenance may require N20 inhaled anesthesia & opioids
no impair on renal or hepatic function
opioids
IV
MORPHINE & FENTANYL
potent analgesics
used in combinations
morphine + N2O = cardiac surgery
respiratory depressant (reversed by naloxone)
neuroleptanalgesia
combination of 2 or more drugs -> decrease side effects & increase activity of both
consciousness + sedation
potent tranquilizer (neuroleptic) + potent narcotic analgesic (droperidol) + fentanyl (innovar)
minor surgery (bronchoscopy + burn dressing)
BZS
IV
DIAZEPAM & LORAZEPAM
bind to bz receptors to potentiate GABA = hyperpolarization & cns inhibition
used in: preanesthesia, balanced anesthesia, operations with no required analgesia -> endoscopy
