General Anesthetics Flashcards
List characteristics of general anesthesia.
- amnesia
- analgesia
- unconsciousness
- inhibition of sensory and autonomic reflexes
- skeletal muscle relaxation
Understand the pharmacokinetics of inhalant anesthetics.
MOA
- GABAa agonist (increases Cl- influx => hyperpolarization => increased IPSP)
DISTRIBUTION
- solubility (more soluble in blood => slower transfer; more lipid-soluble => faster transfer)
- ex: NO not soluble => won’t stay in blood long b/c no space => pushed into brain faster
- ex: halothane soluble => needs to build up in blood to reach a partial pressure that will push it into the brain => takes longer - PP difference (higher PPD => faster transfer)
- first removed by vessel rich organs (BHLK), then skin/muscle, then fat
=> fatter pt. takes longer to wake up - CO (higher CO => slower transfer)
- higher pulmonary blood flow => more diffusion across alveolar capillaries => alveoli emptied out => Fa decreases => brain conc. decreases
ELIMINATION
- low BGPC wash out faster (NO) than high BGPC (halo)
- longer induction = more agent in fat => if fatter pt. takes longer to emerge
- after 100% oxygen give, order of agent elimination is BHLK, S/M, F
How does the blood:gas coefficient influences the onset of action (and termination) for inhaled anesthetics?
BGPC = ratio of anesthetic concentration in blood compared to gaseous phase (when in partial pressure equilibrium)
BGPC > 1 = the more soluble in blood = more of it must be dissolved in blood to raise its partial pressure difference = blood tension rises slowly = longer time to induce (ex: halothane)
BGPC
How do the ventilation rate influence the onset of action for inhaled anesthetics?
VENTILATION
- increase ventilation => slight increase in arterial tension if agent has low blood solubility => not much faster induction (NO)
- increase ventilation => significant increase in tension if agent has high blood solubility => faster induction (halothane)
How does blood flow to a tissue influence the tension of an anesthetics gas in that tissue?
higher blood flow = slower induction b/c faster diffusion across alveolar capillaries => less left to measure Fa => less brain concentration
Describe the following for halogenated hydrocarbons:
- drug names
- associated adv/disadv
DRUGS - halothane, isoflurane, desflurane, sevoflurane
HALOTHANE
- pleasant smell
- nonirritating
- sensitizes myocardium to catecholamines
- liver necrosis
ISOFLURANE
- pungent odor
- medium rate of onset and recovery
- does NOT raise ICP
DESFLURANE
- rapid recovery
- pungent
- low volatility
- irritating
- increased sympathetic input to the heart
SEVOFLURANE
- rapid onset and recovery
- pleasant smell
- preferred for brief procedures
- minimal cardiac effects
Describe the following for inert gas:
- drug names
- advantages
- disadvantages
- clinical indications
- contraindications
NAME - nitrous oxide
ADVANTAGES
- rapid induction and emergence
- pleasant
- good analgesic, but high concentrations excite (laughing gas)
- does not increase ICP
DISADVANTAGES
- incomplete
Describe the following for ultrashort-acting barbiturates:
- drug names
- advantages
- disadvantages
- clinical indications
- contraindications
NAMES - thiopental, methohexital
ADVANTAGES
- rapid due to lipid-solubility and diffusion across BBB
- reduces ICP
DISADVANTAGES
- poor analgesics; can increase sensitivity to pain
- can cause coughing
- venodilation and cardial depression
- not used in US b/c thiopental is lethal injection
List the sedative hypnotics
ketamine
etomidate
propofol
Define MAC. What does and does not affect it?
MAC - minimum concentration of the drug in the alveoli at needed to prevent movement upon a noxious stimulus (i.e. incision) by 50% of the population
- normally, multiplied by 1.3 to achieve ED95
- combined inhalants have an additive effect
- can compare doses between agents (the higher the MAC, the more dose needed to achieve the same efficacy)
FACTORS THAT CHANGE MAC
- body temperature
- age
- drugs
FACTORS THAT DO NOT CHANGE MAC
- sex
- species
- state of oxygenation
- acid-base changes
- arterial BP
List some ways to increase delivery to the brain.
- increased partial pressure difference
- increased volume/min delivered
- decreased CO
- decrease temperature (decreased MAC)
Define the Fa/Fi ratio.
Fa = alveolar concentration = brain concentration Fi = inspired concentration
if Fa decreases, brain concentration ecreases
List the stages of general anesthesia administration.
- preoperative anxiolytic (with or without analgesic) = anti-anxiety for pt’s comfort
- pre-oxygenate/de-nitrogenate = fill up lungs with oxygen to help pt. tolerate 8-10 min. of apnea
- induction = IV anesthesia (if kids, inhalant first)
- maintenance = muscle relaxant + intubation
- emergence = breathe in 100% oxygen and breathe out anesthesia
- recovery
Describe ketamine.
- hypnotic
- NMDA agonist
- dissociative anesthesia (look awake but don’t remember)
- rapid induction makes it good for short procedures and pain
- bronchodilator (keeps them breathing = used for asthma)
- increased cerebral O2, flow, and ICP
- increased BP and HR
- not good for psych patients (bad dreams, salivation, twitchy
Describe etomidate.
- hypnotic
- GABAa agonist
- least CV side effects
- vasoconstriction
- decreased cerebral O2
- adrenal suppression
