9/6 General Anesthetics - Kiss Flashcards Preview

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Flashcards in 9/6 General Anesthetics - Kiss Deck (19):
1

two types of general anesthesia

1. inhaled

  • chloroform used to be the big one, but fell out of use bc of liver issues

2. IV

2

drug list

 

inhaled

  1. nitrous oxide
  2. isuflurane
  3. sevoflurane
  4. desflurane

3

drug list 

 

IV

  1. propofol
  2. etomidate
  3. ketamine
  4. dexmedetomidine

4

5 major effects of GA

1. unconsciousness

2. amnesia

3. analgesia

4. attenuation of autonomic reflexes → reduces chances of bleeding out!

5. skeletal muscle relaxation

5

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

6

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)

7

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

8

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

9

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

10

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

11

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!

12

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

13

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

 

 

14

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)

 

15

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

16

propofol

2,6 diisopropylphenol

"milk of amnesia"

  • used for induction/maintenance and sedation
  • **use within 8 hours of dispensing to avoid bacterial contamination!

characteristics:

  • GABA agonist
  • non-analgesic
  • amnestic
  • system effects
    • cardio: vasodil, neg inotropy
    • resp: decreased tidal vol, RR, minute vol
    • decreased upper airway reflexes
  • antiemetic

17

etomidate

  • induction and short sedation
  • minimal hemodynamic effects (HR, BP, inotropy) → good call for someone who is hemodynamically unstable

characteristics:

  • GABA agonist
  • non-analgesic
  • potential endocrine effects (hypoadrenal syndrome)
    • dose-dep inhibition of 11-b-hydroxylase (cholesterol → cortisol), which limits use for prolonged sedation
  • resp depressant
  • burns on injection
  • associated with increased PONV (postop nausea/vomiting - Vomidate!)

18

ketamine

phencyclidine derivative (angel dust!)

  • used sparingly

 

  • dissociative anesthesia w/ nystagmus
  • NMDA receptor antagonist → ANALGESIC
  • incr HR, BP, CO
  • minimal if any resp depression

19

dexmedetomidine

sedation or adjunct to GA

alpha2 agonist

  • receptors in locus ceruleus and spinal cord

sedative AND analgesic

  • especially good because preserves resp drive

significant decreases in BP and HR

context sensitive half time significantly increased after 8hr

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