general anesthetics

Question 1

general anesthesia - definition

Answer 1

• generalized, reversible CNS depression; all sensory perception is removed
• only used to facilitate surgery/ surgical procedures; has no therapeutic or diagnostic purpose unto itself

Question 2

5 progressive phases of anesthesia

Answer 2

• sedation: pre-operative anxiolysis to facilitate induction
• induction: sedation and rapid loss of consciousness
• paralysis: total relaxation and loss of control of musculature with marked immobility; requires intubation
• maintenance: with inhalation anesthetics
• recovery: patients regain senses and muscle control

Question 3

mechanisms of action

Answer 3

• facilitate GABA: enhance the inhibitory effect of GABA binding to GABA-a; open Cl- channels, allows influx of Cl-; results in lowered membrane potential; makes it harder to depolarize and propagate an action potential
• inhibit glutamate: inhibits the excitatory effects of glutamate binding to NMDA/AMPA receptors; allows influx of Na+ and Ca++ and efflux of K+; results in higher resting membrane potential / facilitates propagation of action potentials
• facilitate 2-pore K+ channels: allows influx of Na+ and efflux of K+; results in overall lowered neuronal membrane potential; makes it harder to depolarize and propagate an action potential

Question 4

4 stages of anesthesia: (list)

Answer 4

stage I: analgesia/ induction
stage II: excitement/ delirium
stage III: surgical anesthesia
stage IV: overdose/ medullary depression/ paralysis

Question 5

4 stages of anesthesia: stage I

Answer 5

pt is conscious but drowsy. variable amnesia.

Question 6

4 stages of anesthesia: stage II

Answer 6

dangerous stage due to risk of laryngospasm and vomiting; efforts made to limit this stage

• pt experiences delirium; may exhibit violent combative beh; hyper-reactive / uncontrolled mvmts; elevated/irregular bp and resp rate

Question 7

4 stages of anesthesia: stage III

Answer 7

ideal stage for surgery; no spontaneous mvmt, no effect (stable) on heart rate and MAP; further CNS depression results in progressive loss of muscle tone and reflexes

Question 8

4 stages of anesthesia: stage IV

Answer 8

loss of spontaneous respirations, profound drop in bp, death

Question 9

IV anesthetics (list of 5)

Answer 9

• used as induction agents or for pre-procedural anxiolysis

benzodiazepines (GABA-a receptor)
barbiturates         (GABA-a receptor)
etomidate            (GABA-a receptor)
propofol               (GABA-a receptor)
ketamine              (NMDA receptor)

Question 10

midazolam

Answer 10

• short-acting benzodiazepene

- for anesthesia induction or conscious sedation

Question 11

lorazepam

Answer 11

• intermediate-acting benzodiazepene
• pre-op sedative
• amnestic

Question 12

diazepam

Answer 12

• long-acting benzodiazepene
• pre-op sedative
• long half life due to active metabolites

Question 13

flumazenil

Answer 13

• benzodiazepene antagonist used for reversal or overdose

Question 14

thiopental

Answer 14

• most common barbiturate for induction
• no reversal agent
• short onset of action and duration
• facilitates GABA activity, also depresses brainstem activity

side-effects:

• severe post-op n/v (treat with serotonin antagonist)
• ** no increase in ICP / specific indication for head trauma
• profound respiratory depression
• dose-dependent decrease in MAP

Question 15

etomidate

Answer 15

• induction agent favored for pts at risk for hypotension (elderly, other pts with limited cardiac reserve)
• short onset of action and duration
• increases affinity of GABA for its receptor
• ** no effect on BP
• minimal effect on heart and respiration
• greater margin of safety than barbiturates, greater post-op n/v than barbiturates
• pain on injection (use with lidocaine)

Question 16

propofol

Answer 16

• most common induction agent
• facilitates action of GABA
• ** rapid onset 30 sec
• ** rapid recovery 4-8 min
• side-effects: ** anti-emetic effect, cardiac depression, hypotension, impaired baroreflex, pain on injection (use with lidocaine)
• fospropofol: inactive, pro-drug form of propofol, converts to propofol in vivo

Question 17

ketamine

Answer 17

• NMDA receptor antagonist
• dissociative anesthetic best suited for asthma pts, children undergoing short and painful procedures
• pt may appear conscious with eyes opened but is unable to respond to sensory stimuli
• can be administered IV, IM, PO, PR

side-effects: effective analgesic; bronchodilation, **hypertension, increased HR and CO, increased cerebral blood flow and ICP; post-op hallucination, vivid dreams, excitation, NO pain with injection (no need for lidocaine)

Question 18

inhalational anesthetics (list of 4)

Answer 18

• used for maintenance of anesthesia only
• excreted by expiration
• very dangerous / very small therapeutic index
• very steep dose-response curve
• NO antagonist

nitrous oxide (non-halogenated)
desflurane (halogenated)
sevoflurane (halogenated)
isoflurane (halogenated)

Question 19

Minimum Alveolar Concentration (MAC)

Answer 19

• describes the potency of inhalational anesthetics
• MAC of 1 (vol %) = minimum concentration preventing muscular response to a standard surgical incision in 50% of unparalyzed patients
• low MAC = high potency
• high MAC = low potency

Question 20

factors that increase MAC

Answer 20

• these factors make the pt LESS sensitive to inhalational anesthetics

hyperthermia (greater than 42C)
drugs that increase CNS activity (catecholamines)
chronic ethanol use
pregnancy

Question 21

factors that decrease MAC

Answer 21

• these factors make the pt MORE sensitive to inhalational anesthetics

hypothermia
advanced age (30% fatality in pts > 80 yrs)
acute ethanol intoxication
second gas effect (when two inhaled anesthetics are mixed, both become more potent)

Question 22

factors that do NOT effect MAC

Answer 22

gender
height
weight
duration of anesthesia
thyroid gland dysfxn

Question 23

nitrous oxide (N2O)

Answer 23

• non-halogenated
• NMDA antagonist
• very high MAC 105% (even if given at 100%, half of pts will still not lose muscular response to surgical incision; would have to be given with hyperbaric technique to achieve no muscular response in 50% of patients to increase the concentration sufficiently. because inhaled anesthetics must be mixed with minimum 20% oxygen to support life, N2O can never be given alone, only used with other inhalational anesthetics to achieve potency via second gas effect)
• ** does not trigger malignant hyperthermia
• will increase BP, CO when mixed with halogenated inhalational anesthetics
• will decrease BP, CO when mixed with opioids

Question 24

halogenated / “volatile” inhalational anesthetics (characteristics)

Answer 24

• MOA: activation of GABA-a and two-pore K+ channels

side-effects:

• dose-dependent drop in BP
• moderate bronchodilation & skeletal muscle relaxation
• respiratory depression
• can affect pregnancy/ crosses placenta; increased miscarriage rates in female OR workers
• ** can trigger hyperthermia (treat with DANTROLENE)

Question 25

desflurane

Answer 25

- halogenated inhalational anesthetic | - rapid onset, rapid recovery

Question 26

sevoflurane

Answer 26

- halogenated inhalational anesthetic | - rapid recovery, no tachycardia

Question 27

isoflurane

Answer 27

- halogenated inhalational anesthetic | - most common inhalational anesthetic used globally