11- General Anesthetics

Question 1

desflurane

Answer 1

Volatile Anesthetic
-main MOA=GABA agonist
-pungent anesthetic (may precipitate increased salivation,breath holding,laryngospasm).
-MAC= 6%
-B:G= 0.42
+Most rapid inhaled anesthetic (fastest onset/offset)
-minimal myocardial depression; can stimulate SNS and increase endogenous catechol’s leading to tachycardia and possibly HTN.
-0.02% metabolized: not a threat for toxic metabolites.
-Very high vapor pressure (upper 600’smmHg) so must be pressurized.

Question 2

sevoflurane

Answer 2

Volatile Anesthetic
-main MOA=GABA agonist
-not pungent to the patient
-MAC= 2%
-B:G= 0.69
  \+Very rapid onset/offset.
-Minimal myocardial depression.
-2% metabolism: theoretically more biproduct produced from metabolism.
-Ideal agent for inhalation induction.
-Does not actually cause renal dysfunction/failure (Compound A not shown to be issue in humans, only in rats in labs).

Question 3

isoflurane

Answer 3

Volatile Anesthetic
-main MOA=GABA agonist
-semi-pungent to patient.
-MAC=1.14%
-B:G= 1.4
+Slowest onset of the volatiles, but most soluble. This leads to a slower uptake and anesthetic effect,and will accumulate more in fat with increased exposure.
-Mild myocardial depression, and negative chronotrope
-0.2% metabolism
-can cause cause vasodilation (may precipitate tachycardia 2/2 barorecptors responses).

Question 4

N2O (nitrous oxide)

Answer 4

Non-volatile anesthetic
-MOA: antagonistic of NMDA
-MAC= 105%; B:G=0.47; F:B=2.5
-Can allow you to decrease your volatile agents to avoid HOTN/myocardial depression.
-Essentially no myocardial depression/HOTN with use.
-Possibility to lead to hypoxia with discontinuation (elimination rapid and leads to dilution of O2 and CO2).
+Can be avoided by administering 100%FiO2 to flush out upon discontinuation.
-Can rapidly expand air pockets (i.e. pneumothorax, pneumocephalus, etc).
+may increase size of Pneumothorax by 2-3x in 15-20”
-Austin’s Favorite Notecard!!!

Question 5

etomidate (Amidate)

Answer 5

Induction agent
-MOA: enhances the effects of GABA
-rapid onset sleep (30-60 secs) and rapid awakening
-hydorlized to inactive metabolites by ester hydrolysis
-75% protein bound, T1/2 75 min; 85% renal excretion
-CV Fx: dec/even SBP, SVR; inc/even HR
-Pulm. Fx: minimal resp. depression
-CNS Fx: dec. CBF, ICP, CMRO2
Induction: 0.2-0.4 mg/kg
-can cause myoclonus and adrenal suppression

Question 6

ketamine

Answer 6

Induction agent
-MOA: “Dissociative Anesthetic”, works on NMDA, opioid, monoaminergic, muscarine receptors, and VGCa channels
-extremely lipid soluable and metabolized in liver to norketamine
-T1/2 2-3 hrs with 90% renal excretion
-CV Fx: inc. SBP, HR, SVR
-Pulm. Fx: no resp. depression
CNS Fx: inc. CBF, ICP, CMRO2
-Induction: 1-3 mg/kg IV; 4-8 mg/kg IM
-Adjunctive analgesic: 0.2-0.5 mg/kg
-can cause emergence delirium (pre-treat with midazolam)

Question 7

methohexital (Brevital)

Answer 7

Induction agent (barbiturate)
-MOA: interact with GABAa receptor which causes hyperpolarization d/t Cl- channels being open longer
-highly lipid soluable so rapid CNS penetration (30 secs)
-quick awakening after single dose
-metabolized by liver (inactive) and excreted by kidneys
-CV Fx: dec. SBP, SVR; inc. HR
-Pulm. Fx: rapid, profound Resp. depression
-CNS Fx: dec. CBF, ICP, CMRO2
Renal Fx: modest dec. in renal blood flow
-Induction: 1-1.5 mg/kg
Beware: extravasation and contraindicated in Acute Intermittent Porphyria

Question 8

propofol (Diprivan)

Answer 8

Induction agent

• MOA: Interaction with GABA inc. open Cl- channels and acts as Na+ channel blocker causing membrane hyperpolarization
• 95-99% protein bound
• T1/2 30-60min but redistribution renders it ineffective much more quickly
• metabolized via glucoronidation in the liver, renal excretion
• CV Fx: dec. SBP, MAP, SVR with level HR
• Pulm. Fx: dose dependent Resp. depression
• CNS Fx: dec. CBF, ICP, CMRO2 (good for neuro cases)
• Induction: 1.5 to 2.5 mg/kg
• Continuous: 25-100 mcg/kg/min= sedation, 100-300 mcg/kg/min= anesthesia (TIVA)

Question 9

thiopental (Pentothal)

Answer 9

Induction agent (barbiturate)
-MOA: interact with GABAa receptor which causes hyperpolarization d/t Cl- channels being open longer
-83% protein bound to albumin
-highly lipid soluable so rapid CNS penetration (30 secs)
-quick awakening after single dose
-metabolized by liver (inactive) and excreted by kidneys
-CV Fx: dec. SBP, SVR; inc. HR
-Pulm. Fx: rapid, profound Resp. depression
-CNS Fx: dec. CBF, ICP, CMRO2
Renal Fx: modest dec. in renal blood flow
-Induction: 3-5 mg/kg
Beware: extravasation and contraindicated in Acute Intermittent Porphyria