9/6 General Anesthetics - Kiss Flashcards
two types of general anesthesia
- inhaled
* chloroform used to be the big one, but fell out of use bc of liver issues - IV
drug list
inhaled
- nitrous oxide
- isuflurane
- sevoflurane
- desflurane
drug list
IV
- propofol
- etomidate
- ketamine
- dexmedetomidine
5 major effects of GA
- unconsciousness
- amnesia
- analgesia
- attenuation of autonomic reflexes → reduces chances of bleeding out!
- skeletal muscle relaxation
ideal general anesthetic agent
- rapid, smooth loss of consciousness
- rapidly reversible on discont
- wide margin of safety
right now, don’t have any GA that meet all of these criteria
balanced anesthesia
diff agents have diff strengths/weaknesses → instead of buying into one entirely, most anesthesiologists employ a mix in order to…
- max efficacy
- min side effects
balanced anesthesia: utilization of small dozes of mulitple agents (inhaled and/or IV)
inhaled anethetics
subtypes
1. gaseous (gas at room temp)
- biggest adv: QUICK on, QUICK off
- currently, only NO (low potency, used in addtn to other agents)
- xenon is experimental
- good amnestic, analgesic action
2. volatile (liq at room temp)
- halogenated ethers, mostly fluorinated
- isoflurane, sevoflurane, desflurane most commonly used
- mostly for maintenance in adults
- exception: in peds → used for induction
inhaled anesthetics PK
onset
- driving force for uptake
- anesthesiologist controlled parameters
- agent controlled parameters
driving force for uptake to target organ (CNS) is alveolar fraction of anesthetic (alv partial pressure; FA)
implication: alv is the point of entry! the greater alv fraction you’re able to achieve, the higher your uptake will be!
anesthesiologist can affect:
- inspired fraction (FI)
- alveolar ventilation
anesthetic factors that determine onset:
- solubility of inhaled agent (blood:gas partition coeff)
- more insol → faster onset
- most insol → “fill the well” faster
- ISO (isofluorine) > SEVO > DES > N2O
inhaled anesthetics
PK
emergence
reverse of onset
- no inspired fraction (bc you’re trying to get person out of anesthesia)
- alveolar ventilation is the key!!!
- metabolism is a minor factor
degree of metabolism: SEVO > ISO > DES > N2O
MAC
pharmacodynamic concept
minimal alveolar concentration
- partial pressure of inhaled_anes in alveoli at which 50% of a pop of non-relaxed patients remain immobile at skin incision
measure of POTENCY
LOWER MAC = higher potency
inhalational anesthetics
PD : effect on organ systems
4 systems: names and effects
CV system
- decrease in BP (due to lowered systemic vasc resistance
- negative inotropy)
resp system
- incr RR
- decr tidal volume
- overall decrease in minute volume
hepatic system
- decr in portal v flow
- incr in liver enzymes
uterine sm muscle
- decr in uterine tone → helpful during delivery BUT can lead to increased bleeding!
inhaled anesthetics
adverse effects/tox
reports of organotox, mutagenicity, carcinogenicity mostly in animal studies with little human correlation
NO : potential decrease in methionine synthase → megaloblastic anemia
malignant hyperthermia
what is it
etiology
antidote
incidence
hypermetabolic syndrome in genetically susceptible individs after exposure to triggering agents
- halogenated inhalationals
- succinylcholine
etiology: decreased reuptake of Ca from sarcoplasmic reticulum
* sustained muscle contraction → hyperthermic, hypercapnic, hypoxic, hyperkalemic
antidote: dantrolene
- can still give GA, but stay away from triggering agents!
rare indicence, but need to ask about family hx
IV anesthetics
3 major drugs
onset (tissue preference)
preferred method of induction
PROPOFOL, ETOMIDATE, KETAMINE
- all lipophilic, all rapid onset of action
- preferential partitioning into highly perfused, lipophilic tissues (brain, spinal cord)
IV anesthetics
elimination
rapid redistribution from highly perfused tissues → lean tissues
- implication: quick offset of action
liver metabolism is also rapid, but occurs later
context-sensitive half-time: length of time req for conc to drop by half after discontinuation of infusion
