Pharm: Anesthetics Flashcards
alveolar concentration
depends on Fa (alveolar concentration) / Fi (inspired air concentration)
The faster FA/FI approaches 1, faster anesthesia will occur
blood:gas partition coefficient
blood:gas
affinity for blood compared to inspired gas - the smaller the number the lower the blood solubility = fast onset of action
there is an inverse relationship b/w partition coefficient and rate of anesthesia onset!
ex:
- low blood solubility (nitrous oxide, desflurane) = fast onset of action
- high blood solubility (halothane) = slow onset of action
nitrous oxide
gaseous anesthetic - low affinity for blood
MAC>100 (would require more than 100% of atmosphere they are inhaling to reach 1 MAC - must use balanced anesthesia)
- low blood:gas coeff = rapid onset and recovery
- incomplete anesthetic
desflurane
inhaled anesthetic
MAC= 6-7
** blood:gas = 0.42
- low volatility, poor induction agent, rapid recovery
sevoflurane
inhaled anesthetic
MAC = 2
** blood gas = .69 - rapid onset and recovery
isoflurane
inhaled anesthetic
MAC = 1.4
** medium rate of onset and recovery (1.4)
enflurane
inhaled anesthetic
MAC=1.7
** medium rate of onset and recovery (1.8)
halothane
inhaled anesthetic - high affinity for blood
MAC=.75
** medium rate of onset and recovery (2.3)
ADR: hepatitis!!!
increased CO
↑ pulmonary blood flow
↑ uptake of anesthetic
↓ rate of FA/FI rise
↓ rate of induction
** an increase in CO and pulmonary blood flow will increase the uptake of anesthetic into the blood, but the anesthetic taken up will be distributed in all tissues, no just the CNS; increased CO will thus increase delivery of anesthetics to OTHER tissues and not the brain
recovery from anesthesia?
- lungs are major route for elimination–> can speed up through hyperventilation
- If relatively insoluble in blood and brain –> eliminated faster
- Time to recovery depends on elimination from brain
- some drugs are also eliminated via hepatic metabolism (halothane being the most)
minimum alveolar concentration
- 0 MAC = partial pressure of inhaled anesthetic, 50% of population remain immobile at skin incision
- Value expressed as volume %
** Successful anesthesia = 0.5 – 2 MAC
MAC is additive: 0.5 MAC of x + 0.5 MAC of y = 1 MAC
stages of anesthesia?
Stage I Analgesia
Analgesia without amnesia; later will experience both
Stage II Excitement
Delirious, completely amnesic; rapid respirations; HR and BP increase
Stage III Surgical Anesthesia
Slowing RR and HR, extends to apnea
Stage IV Medullary Depression
Requires circulatory and respiratory support
propofol
IV anesthetic
- preferred for continuous infusion d/t half time not being affected by infusion duration
- can cause hypotension
MOA: Potentiation of Cl- current mediated through GABAA receptor complex
- Fast onset, fast clearance
Organ System Effects:
CNS – no analgesia; EEG burst suppression
CV – hypotension
Respiratory – depressant
Thiopental
barbituate - IV anesthetic
MOA:
Act on GABAA receptor to increase duration of channel opening
Organ System Effects:
- CNS – sedation; no analgesia: Decrease electrical activity on EEG (exception methohexital)
- Respiratory – depressant (apnea)
methohexital
barbituate - IV anesthetic
MOA:
Act on GABAA receptor to increase duration of channel opening
Organ System Effects:
- CNS – sedation; no analgesia: Decrease electrical activity on EEG (exception methohexital)
- Respiratory – depressant (apnea)
Midazolam
IV anesthetic - benzodiazepine
** rapid onset of action ** best for infusion if using benzo d/t shortest context sensitive half time
MOA:
Acts on the GABAA receptor, increases receptor sensitivity to GABA (agonist), enhances inhibitory neurotransmission
Organ System Effects:
- CNS – potent anticonvulsants
- Respiratory – depression may occur when given with opioids
lorazepam
IV anesthetic - benzodiazepine
** rapid onset of action **
MOA:
Acts on the GABAA receptor, increases receptor sensitivity to GABA (agonist), enhances inhibitory neurotransmission
Organ System Effects:
- CNS – potent anticonvulsants
- Respiratory – depression may occur when given with opioids
diazepam
IV anesthetic - benzodiazepine
** rapid onset of action **
MOA:
Acts on the GABAA receptor, increases receptor sensitivity to GABA (agonist), enhances inhibitory neurotransmission
Organ System Effects:
- CNS – potent anticonvulsants
- Respiratory – depression may occur when given with opioids
etomidate
IV anesthetic
MOA:
GABA like effects, potentiation of GABAA mediated Cl- currents
** minimal impact of CV function!!! useful for pts w/ cardiac instability
Organ System Effects:
- CNS – cerebral vasoconstrictor
- CV – minimal impact on hemodynamics
- Endocrine – adrenocortical suppression
ketamine
IV anesthetic
MOA:
Inhibits NMDA receptor complex
** fast onset of action !
Organ System Effects:
- CNS – profound analgesia!!! cerebral vasodilator
- -> Emergence reactions; dissociative anesthesia
- can have scary dreams and hallucinations!!
- CV – increase systemic BP, HR, CO; however, is a direct myocardial depressant
Dexmedetomidine
IV anesthetic
MOA:
Highly selective α2-adrenergic agonist
** causes hypnosis and analgesia - useful in pts. transitioning to extubation
Organ System Effects:
- CNS – hypnosis, analgesia, activates endogenous sleep pathways
- CV – decrease in HR and SVR
Benzocaine
LA - ester
** surface use only!
cocaine
LA - ester
** low potency, medium DOA
procaine
LA - ester
** low potency, short DOA
tetracaine
LA - ester
** high potency, long DOA
bupivicaine
LA - amide
** highly potent, long acting
lidocaine
LA - amide
- lower potency, medium DOA
- also available as patch
ropivacaine
LA - amide
** high potency, long DOA
laprascopic hernia repair, first time undergoing surgery and is highly anxious?
use benzodiaepine - midazolam
IV drug that is rapid in onset and recovery w/ antiemetic actions?
Propofol
chemical w/ which blood:gas partition will reach the highest concentration in brain the fastest?
the one with the lowest coeff. b/c that means it isn’t highly bound to blood
which agent lacks ability cause CNS depression, or level of consciousness or level to reduce pain
pancuronium
why can’t NO be used alone for general anesthesia?
MAC is greater than 100%
