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Flashcards in General Anesthetics (Kiss) Deck (13):
1

Understand the five major effects of a general anesthetic.

1. Unconsciousness
2. Amnesia (memory loss)
3. Analgesia
4. Attenuation (gradual loss) of autonomic reflexes
5. Skeletal muscle relaxation (for ease of surgery)

2

Differentiate between sedation and general anesthesia.

Conscious sedation: minimal amounts of amnestic and opioid; patient still able to converse, respond to stimuli and commands (RESPONSIVE); able to protect airway and maintain ventilation

Continuum through GA involves -> decreases in responsiveness to painful stimuli and commands (still ability to protect airway and maintain normal ventilation)

GA: once patient has lost ability to protect the airway

3

Inhaled: Differentiate between a gaseous and volatile anesthetic.

Inhaled Anesthetics -

Gaseous:
- Gas at room temp
- currently only agent is NO - relatively low potency, used in addition to other agents
- Main (+): really good on and off
- Good amnestic and analgesic actions
- Xenon = experimental

Volatile:
- Liquid at room temp
- halogenated ethers (mostly fluorinated)
- isoflurane, sevoflurane, desflurane = most commonly used
- used primarily for maintenance, except in pediatrics -> used for induction

4

Understand the major factors involved in the onset of and emergence from an inhalation anesthetic.

ONSET: Fa (alveolar fraction of anesthetic) = driving force for uptake of inhaled anesthetics to its target organ (CNS) - the more you put in, the faster it will be taken up

Anesthesiologist controlled parameters:
- Inc. Fi (INSPIRED FRACTION) - take vaporizer and inc to max
- Inc. ALVEOLAR VENTILATION - the faster the ventilation, the more you are pouring in

Agent dependent parameters:
- Solubility of inhaled agent (more insoluble agents have faster onset - can get to target organ faster)
- Solubilities: ISO (takes the longest onset) >SEVO>DES>NO

EMERGENCE: onset in reverse, except Fi = zero
- Alveolar ventilation = most important factor
- Metabolism = minor factor
- Degree of metabolism: SEVO>ISO>DES>NO

5

Pharmacodynamics: Be able to explain the concept of MAC (minimal alveolar concentration).

Measure of potency = equipotent dose of inhaled anesthetic

Partial pressure of inhalation anesthetic in the alveoli at which 50% of a population of NON-RELAXED patients remain immobile at skin incision

Higher MAC means less potent (b/c you need more anesthetic to get the same effect)

6

Understand the effects of inhaled agents on major organ systems.

CV: decrease in BP (as a result of decreased SVR (systemic vascular resistance) and negative isotropy)

Respiratory: increased RR, decreased Vt (tidal volume), for an overall decrease in minute volume

Hepatic: decrease in portal vein flow; increase in liver enzymes rarely seen

Uterine smooth muscle: decrease in uterine tone (helpful during delivery) but may lead to increase in uterine bleeding

7

Become familiar with concept of MH (Malignant Hyperthermia).

Hyper metabolic syndrome in genetically susceptible patients after exposure to triggering agents (halogenated inhalationals and succinylcholine)

Incidence is rare

Caused by a decrease in reuptake of Ca2+ from SR (sustained skeletal muscle contraction - every muscle in the body is tight)

8

Understand the concept of balanced anesthesia.

Utilize small doses of multiple agents, both inhaled and IV to minimize side effects and maximize efficacy (each drug has a specific strength)

Basically customized agent combination

9

Understand the nature of the onset of and emergence from IV anesthetics.

Propofol/etomidate/ketamine onset:
- all three lipophilic
- preferential partitioning into highly perfused lipophilic tissues (brain and spinal cord)
- rapid onset of action

elimination:
- rapid redistribution from highly perfused tissues into lean tissues for quick offset of action
- liver metabolism is rapid
- good context sensitive 1/2 time _> describes the elimination 1/2 time after a continuous infusion (aka give something for 2 hours but takes 2 days to eliminate)

10

Be able to explain the major differences between the IV anesthetic agents:

PROPOFOL

Propofol:
- "Milk of Amnesia"
- Used for induction and maintenance of GA as well as sedation
- important to use within 8 hours of dispensing to prevent bacterial contamination
- GABA agonist
- non-analgesic (will feel the needle prick)
- amnestic (will forget the needle prick)
- CV: vasodilatory and negatively inotropic
- DECREASE IN BP
- Respiratory: decrease in Vt, RR, and minute volume
- Decrease in upper airway reflexes
- Antiemetic (effective against vomiting and nausea)

NOT meant for sleep inducing (michael jackson)

11

Be able to explain the major differences between the IV anesthetic agents:

ETOMIDATE

Etomidate ("vom"-idate)
- Used for induction and short sedation
- Minimal hemodynamic effects i.e., HR, BP, inotropy (BP stays where it is)
- GABA agonist
- Non-analgesic
- potential endocrine effects: dose dependent inhibition of 11 B hydroxyls (cholesterol to cortisol pathway inhibited) which limits its use for prolonged sedation
- Respiratory depressant
- Burns on injection
- Associated with increased PONV

12

Be able to explain the major differences between the IV anesthetic agents:

KETAMINE

Ketamine:
- used SPARINGLY (as primary, limited use)
- Phencyclidine derivative (angel dust) - might start telling you dreams (when they come to, either feel floating looking down on surgery or... paranoia) - so co-administration with a benzodiazepine
- Dissociative anesthesia w/ nystagmus (cataleptic state)
- NMDA receptor antagonist
- Analgesic
- Increases in HR, BP, and CO (INCREASE IN BP!)
- Minimal if any respiratory depression
- Lacrimation and secretions increased

13

Be able to explain the major differences between the IV anesthetic agents:

DEXMEDETOMIDINE

Dexmedetomidine
- Used for sedation or adjunct to GA
- Alpha-2 agonist
- Both sedative and analgesic
- Receptors in locus ceruleus and spinal cord
- Preserves respiratory drive
- Significant decrease in BP and HR can be seen
- Context sensitive 1/2 time is significantly increased after 8 hrs of infusion