General Anesthetics I Flashcards
What is anesthesia
a state where no movement occurs in response to what should be painful
the patient has lost consiousness
absence of memory during anesthesia
amnesia
inability to interepret, respond to and remember pain
Analgesia
Analgesia is
inable to interpret, respond to and remember pain
During anesthesia you are
immobile to respond to noxious stimuli and you do not activate autonomic responses
Potency is usually measured by determination of the concentration of anesthetic that
prevents movement in response to pain
The ‘dose’ of anestetic that prevents movement in:
in response to pain in 50% of the patients
the dose of a gas is directly related to and determined by :
conc in alveolus
What quantifies anesthetic potency in inhaled anesthetics?
minimal alveolar concentration (MAC) that prevents movement in 50% of pts
Benefits of MAC as measure of potency
Can be continuously monitored by measuring end-tidal anesthetic concentration
Provides a direct correlate to anesthetic concentration at the site of action in CNS
Simple to measure end-point (lack of movement)
How do we measure potency for intravenously administered anesthetics
usually use free plasma concentration that produces loss of response to surgical incision in 50% of subjects as an index of potency.
Common effects shared by all anesthetics include
membrane hyperpolarization and effects on synaptic function; such that inhibitory neurotransmission is increased and excitatory neurotransmission is reduced.
Likely targets of anesthetics
GABAa
NMDA
other channels and membrane proteins
regulated chloride channel function is enhanced by most, but not all anesthetics anesthetics produce allosteric interactions; not a direct effect them
GABAA receptors
Glutamate-regulated cation channel
Anesthetics that do not interact with GABA receptors all inhibit these receptors
NMDA
Most anesthetics will increase _____ opening via allosteric effects to increase Cl- conductance
GABA a
Stages of Genreal anesthesia
Premedication
Induction
Maintaine
Keys for induction
want it to be non-frightening and non painful and we only induce with inhalational anesthetic in emergency, otherwise via IV
To maintain anesthesia with gaseious anesthetics keep in mind
they have short 1/2 lives and need to constantly be administered
All parenterally admin anestetics are
hydrophobic and given as single IV bolus
Single iv bolus results in a high concentration in ________within a single circulation time; results in_____ induction of anesthesia
brain and spinal cord
RAPID
What happens as blood levels of anesthetics drop after induction
As blood levels drop, anesthetic redistributes back into the blood from the brain and winds up in other tissues where it is slowly released and metabolized
the half-life of the anesthetic in the body and the duration of action are
not the same
duration of action is _____ than half life thus multiple dosing is _____
shorter
complex
typical barbituate anesthetic
sodium thiopental
Barbituate used to induce anesthesia; typical induction dose produces unconsciousness in 10 to 30 sec; duration of action of a single dose is about 10 min.
sodium thiopental
1/2 life of sodium thiopental
Has a long half life (12 hours) so can produce residual effects (hang-over) after anesthesia has worn off
When do we reduce the dose of sodium thiopental we give to patients?
Dose should be reduced if patient has been premedicated with other CNS depressants, including opiates, benzodiazepines and alpha2 agonists.
Sodium thiopental works by
activating GABAa receptors
Why dont we give intra-arterial injection of sodium thiopental
causes necrosis and inflammation
how can we deliver sodium thiopental to peds patients
rectally
CNS affects of sodium thiopental
Reduces cerebral oxygen utilization, and, as a consequence, reduces cerebral blood flow and intracranial pressure
Has been tried as a protective agent for the treatment of cerebral ischemia
CV affects of sodium thiopental
Vasodialation—espeicially venodialation
**DONT use for pts with reduced pre-load or cardiomyopathy– see severe drop in BP
Can we use barbiutates in pts with coronary artery disease?
yes because its not arythmogenic
Affect on respiration sodium thiopental has
respiratory depression— often need to intubate pts bc they stop breathing
Propofol:
onset and duration:
uses:
Propofol(Diprivan®)
- Onset and duration of anesthesia are the same as barbiturates
- Is used to maintain and induce anesthesia
Is antiemetic, an advantage as many patients are nauseated following surgery
Propofol
Has a shorter half-life than thiopental; used when a rapid return to normal mental status is desired (out-patient surgery, for example)
Propofol
Mech of Propofol
GABAa
Half life of propofol in the body
3.5 hours with much less hangover than barbituates.. HUGE for usefullness in outpatient surgeries
Unique side effect of propofol
pain at injection side thus gven with lidocaine
also causes initial excitaiton upon induciton
pain at injection side thus gven with lidocaine
also causes initial excitaiton upon induciton
Propofol
3.5 hours with much less hangover than barbituates.. HUGE for usefullness in outpatient surgeries
Propofol
CNS side effects of Propofol
CNS: Reduces cerebral oxygen utilization, and, as a consequence, reduces cerebral blood flow and intracranial pressure
CV effects with Propofol
more sever reduction in BP then thiopental
see vasodialtion and depression of myocardial contractility
blunts baroreflexes
What’s the danger in propofol blunting baroreflexes
see depression of myocardial contractility but then they’re not opposed by vasoconstriciton and HR will increase
What type of patients are intolerant to propofol
those intolerant to decreased BP
–contraindicated in pts with hypotension
Respiratory effects of propofol
more depression then thiopental
Primarily used to induce anesthesia in patients at risk for hypotension
Etomidate
has high incidence of pain on injection and myoclonus
etomidate
CNS effects of etomidate
CNS: Reduces cerebral oxygen utilization, and, as a consequence, reduces cerebral blood flow and intracranial pressure
Etomidate has____ respiratory depression than thiopental
Less
Drawback of etomidate
Significantly more nausea and vomiting than thiopental
What is concerning about etomidate post-surgery
ncreased post-surgical mortality due to suppression of the adrenocortical stress response; primarily when the anesthetic has been given for a prolonged period of time. Therefore, only used to induce anesthesia in patients prone to hemodynamic problems
produces dissociative anethesia and profound analgesia
Ketamine
This anethetic produces dissociative anesthesia, doesn’t affect respiration and is a bronchodilator
ketamine
Ketamine is charcterized by:
1) profound analgesia
2) unresponsiveness to commands, even though eyes can be open
3) amnesia
4) spontaneous respiration
Administration of ketamine
typically administered iv but can also be used via intramuscular, oral and rectal routes
Ketamine mech
NMDA receptor anatagonist
Advantages of Ketamine
Advantages: profound analgesia, very little respiratory depression, bronchodilator
Side effects of Ketamine
Produces nystagmus, salivation, lacrimation, spontaneous limb movements and increased muscle tone
increased intracranial pressure
Produces nystagmus, salivation, lacrimation, spontaneous limb movements and increased muscle tone
increased intracranial pressure
Ketamine
causes emergence delierium adn increased BP dt sympathomimetic affect
Ketamine
Ketamine is reserved for pts with
broncospasm that can’t be indubated
good for children undergoing short, painful procedures
Short acting benszo that is a GABAa activator
Midazolam
used alone for conscious sedation, anxiolysis and amnesia for short procedures or as an inducing agent
MMidazolam
Mech of Midazolam
Short acting benszo that is a GABAa activator
good adjunt for local anestheticsm or pre-op to decrease anxiety
midazolam
Compared to thiopental, midazolam has ____ duration of action and _____ induction
longer duration
slower induction
Midazolam must be ______ to it’s active metabolite
Metabolized by hydroxylation to an active metabolite
a. Has been associated with respiratory depression and respiratory arrest especially when used intravenously to produce conscious sedation
Midazolam
Pt population to be careful when administering Midazolam
Should be used with caution in patients with neuromuscular disease; Parkinson’s disease; bipolar disorder
Induction for patient surgery and causes hypotension and hang over
Thiopental
Used for induction/maintence especially outpatient and cuases hypotension and respiratory depression
Propofol
Used for induction in pts that have hypotention but causes nausea and adrenal suppression
Etomidate
Used for pts with broncospasm or in kids for short, painful procedures
Ketamine
Used for cons sedation and as an anti-anxiety but has slow induction with respiratory depression
Midazolam
