36: General Anesthetic Agents Flashcards
anesthesia =
loss of sensation or a state without any feeling
advantages and disadvantages of general v. local anesthesia
local: minimal system disturbance, but may not be adequate
general: body wide anesthesia, but disturbance of all organ systems
general anesthesia =
clinical state where there is an induced loss of consciousness or total insensibility in a reversible manner
general anesthesia is associated with _____ respiration and __________ blood pressure
decreased; decreased
myocardial depression and vasodilation
“triad of anesthesia”
asleep
pain-free
still
6 characteristics of ideal anesthetic agent
- unconsciousness
- amnesia
- analgesia
- skeletal muscle relaxation
- areflexia
- good minute-to-minute control
why are adjuvant drugs used prior to anesthesia?
to make it more safe and pleasant
- relieve anxiety = benzodiazepines
- prevent allergic reactions = antihistaminics
- prevent nausea and vomiting = antiemetics
- provide analgesia = opiods
- prevent bradycardia and secretion = atropine and glycopyrrolate
what kinds of clinical conditions might be important to know about when a patient is to undergo anesthesia?
**prior anesthetic history of patient and blood relatives
- family history of malignant hypothermia
- cardiovascular problems
- respiratory disease
- allergies to medicine and food
4 phases of general anesthesia
- induction
- maintenance
- emergence
- recovery
4 stages of general anesthesia
I: analgesia
II: excitement
III: surgical anesthesia
IV: medullary depression
what are inhalable anesthetics generally used for?
maintenance of anesthesia
can be used for induction in pediatrics
what are IV or fixed anesthetics generally used for?
induction and short surgical procedures
what ion channels may anesthetics alter?
- increase GABAa receptor Cl- channel activity
- activate voltage-gated K channels
- inhibit glutamate NMDA receptors
advantages of inhalable anesthetic agents over IV
+ easy to control depth of anesthesia
+ readily reversible, minute-to-minute control
- induction not as fast or smooth as with fixed agents
increasing inspired anesthetic concentration in inspired air —> _________ partial pressure in lungs —>
increased
faster achievement of anesthetic concentration in the blood
increasing alveolar ventilation —> ____ gas molecules/time —>
more
faster anesthesia onset; better ventilation results in more rapid onset of anesthesia
partial pressure of anesthetics with higher solubility are affected by _______
ventilation rate
what does the otswald coefficient tell you?
solubility in blood
lower otswald coefficient –> _____ soluble —> ______ rise in partial pressure in blood —> ______ equilibration with brain and induction
less; more rapid; faster
ex: NO which is less soluble reaches a higher partial pressure in the blood faster and thus is able to reach anesthetic concentrations in the brain more rapidly
brain:blood partition coefficient is related to…
solubility in lipid
more soluble = more potent
high pulmonary blood flow = ______
lower pulmonary blood flow = _________
slower onset
faster onset
the greater the uptake of an agent, the alveolar concentration rises _________ —> ____ rate of induction
slower
slower
ex: insoluble agents are taken up slowly –> alveolar concentration rises fast –> fast induction
less soluble per otswald coefficient = ______ elimination
faster
what is minimum alveolar concentration MAC?
the concentration of anesthetic in the inspired air at equilibrium when there is no response to noxious stimulus in 50% of patients
lower MAC = ____ potent anesthetic
more
higher lipid solubility = _______ potent anesthetic
more
lower MAC
anesthesia is produced when anesthetic px is brain is ____ MAC
greater than or equal to
MAC values of inhaled anesthetics are _______
additive
ex: nitrous oxide can be used as a carrier gas producing40% of a MAC, therby decreasing the anesthetic requirement of both volatile and IV anesthetics
CNS depressants _______ MAC
decrease
elderly also decreases MAC; young increases
“laughing gas”
nitrous oxide
pros and cons of nitrous oxide
pro: rapid onset and recovery, good analgesia, safe!
con: incomplete anesthetic; insufficient potency for surgical anesthesia, lack of potency
“2nd gas effect”
reduces the induction time for the primary agent
ex: No speeds up mask induction of sevoflurane
decreases: induction time for primary agent, required concentration of primary agent, and toxicity of primary agent
2 major side effects of NO2
- diffusion hypoxia (with abrupt discontinuation it quickly diffuses out of the body into the alveoli and dilutes oxygen)
- increased risk of spontaneous abortion and decreased probability of conception
can NO2 be used as the sole anesthetic agent?
NO
analgesic for minor procedures or EMS
mostly used as complimentary agent
effects of halogenating the volatile agents
- nonexplosive and non-flammable
- increased potency
- increased toxicity and side effects
systemic effects of halothane
decreased CO and hypotension
side effects of enflurane
not as popular as others due to CNS stimulation effects
- EEG convulsive pattern
- jerking
- twitching
fastest onset and recovery halogenated agent
desflurane
advantages and disadvantages for desflurane
+ fastest onset and recovery
+ excellent minute-minute control
- more irritating to respiratory passages than others –> bronchial irritation with cough and laryngeal spasm
why is sevoflurane the most commonly used inhalable anesthetics?
- rapid onset and recovery
- very potent
- excellent controllability due to low solubility and high potency
- low airway irritation –> used for mask induction and those with irritable airway
malignant hyperthermia?
occurs in genetically susceptible individuals with inhalable anesthetics combined with paralytics
what are IV anesthetic used for?
induction! and maintenance of anesthesia
major IV disadvantage
can’t reverse the effects, except via metabolism
what is thiopental used for?
induction - not maintenance or sole anesthetic
does NOT cause any analgesia
“milk of magnesia”
propofol
99.9% of all inductions =
propofol
excellent quality of recovery
which drug causes dissociative anesthesia?
ketamine
characterized by intense analgesia, catalepsy and amnesia
MOA ketamine
non-competetive glutamate NMDA receptor antagonist
what is emergence phenomenon?
unpleasant dreams, hallucinations and disorientationduring emergence
side effect of ketamine
what agent might you want to use for a patient with compromised cardiac status?
ketamine
contraindication for ketamine
psychiatric history
pre-anesthetic medication = adjuvant drug. Why use them?
- increase rate of induction
- decrease anxiety
- decrease pre and post operative pain
- decrease side effects of general anesthetics
- reduce amount of general anesthesia required
what is midazolam good for?
sedation
amnesia
anxiolytic properties
MOA midazolam
potentiation at GABAa receptors
what are the uses for midazolam?
sedation for painful procedures, can be used as induction agent, or substitute for thiopental/propofol in high risk patients
