IV Anesthetics

Question 1

Propofol

Answer 1

MOA: GABAa - open Cl channel
PK: Rapid liver metabolism
-> water soluble
Extrahepatic; lungs (30%), kidneys
Termination of drug effect is redistribution from highly perfused to poorly perfused organs/compartments
CNS: dec. CMRO2-> dec. CBF via preserved flow metabolism coupling => dec. ICP & IOP

Onset: 15-45s Duration: 3-8min (awaken 8-10 min after induction dose) t1/2: 2-24hrs

Dosing:
Induction 1-2.5mg/kg
Maintenance 50-200ug/kg/min
Pedi 2.5-3.5 mg/kg infusion 250 mcg/kg/min
MAC induction- 0.5mg/kg or 100-150 mcg/kg/min
MAC maintenance- 25 - 75 mcg/kg/min
PONV 10-20 mg

Question 2

Midazolam

Answer 2

MOA: GABAa, Cl current- hyper polarize = dec excitability
PK: hepatic microsomal O2 - effected by age, liver dz, multi pharm
Onset: 2min
Duration 15-20min t1/2 1.5-2.5hrs

Dose:
Induction 0.1-0.3 mg/kg
Premed/sedation for regional/brief procedure 1-2mg
Pedi premed 0.5mg/kg

Dec vent response to CO2

Antidote: Flumazenil 8-15 ug/kg

Question 3

Ketamine

Answer 3

MOA: NMDA antagonist  
PK: liver P450 -> norketamine
Onset (45-60s) 1-5min IV/IM
Duration 5-10min      t1/2 2-4hrs
Dosing 
Induction 1-2mg/kg  (4-6mg/kg IM) 
Analgesia adj 0.2-0.8 mg/kg 
Sub analgesic 3-5ug/kg/min - reduce opioids tolerance and opioid induced hyperalgesia

Other: cholinergic, dilated & nystagmic, active metabolite

Question 4

Etomidate

Answer 4

MOA: GABAa
PK: ester hydrolysis -> urine, bile 
Onset: like propofol 
Duration 3-8min, linear w/ dose; 0.1mg/kg = 100 sec unconsciousness 
t1/2 3-5.5hrs
Dosing 
Induction 0.2-0.3mg/kg 

Other: PONV, myoclonus 50%, some vent suppression, dose dependent inhibition of 11B-hydroxylase (last 4-8hrs after induction dose)

Question 5

Dexmedetomidine

Answer 5

MOA: high selective A2 agonist
Analgesic @ lvl of spinal cord
PK: rapid hepatic-> urine/bile

T1/2 2-3hrs
Dosing
GA adj 0.5-1ug/kg over 10-15min then 0.2-0.7ug/kg/hr infusion

Other: bolus assoc inc BP + brady ?peripheral a2. Brady may req tx (unopposed vagal). Vent; dec Vt