General Anesthetics (Kiss) Flashcards
Understand the five major effects of a general anesthetic.
- Unconsciousness
- Amnesia (memory loss)
- Analgesia
- Attenuation (gradual loss) of autonomic reflexes
- Skeletal muscle relaxation (for ease of surgery)
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
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
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
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)
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
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)
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
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)
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)
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
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
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
