Three Compartment Model

1
Three Compartment Model
2
Remifentanil vs. other opioids
100
10
Percent of peak plasma opioid concentration
fentanyl
1
sufentanil
alfentanil
remifentanil
0.1
0
120
240
360
480
600
Minutes since bolus injection
Minto et al, Anesthesiology, in press
3
Three Compartment Modelplus an Effect Site
4
Remifentanil vs. other opioids
100
sufentanil
80
fentanyl
60
Percent of peak effect site opioid concentration
40
alfentanil
20
remifentanil
0
0
2
4
6
8
10
Minutes since bolus injection
Minto et al, Anesthesiology, in press
5
50 effect sitedecrement curves
6
V1 and Clearance decrease with age

• V1 decreases about 20 from age 20 to 80
• Common finding for anesthetic drugs
• Clearance decreases about 30 from age 20 to 80
• Mechanism unknown

7
EC50 decreases with age

• EC50 is a measure ofbrain sensitivity
• Decreased EC50 means increased sensitivity
• Decreased EC50 with age also reported for
• fentanyl
• alfentanil
• sufentanil

8
t 1/2 ke0 increases with age

• t 1/2 ke0 is the time required for the brainto
  equilibrate withthe plasma
• an increase in t 1/2 ke0would be expected
  toresult in a slower onsetof drug effect

9
Age delays onset but does not affect peak
concentration
10
Age Related Changes In Bolus Dose Parameters
11
Bolus doses should be reduced by 50 in the
elderly

• The reduction in bolus dose is because of the 50
  increase in sensitivity in the elderly
• Adjusting the bolus for age is at least as
  important as adjusting it for body weight

12
Age effects on bolus dose
Minto et al, Anesthesiology, in press
13
Age Related Changes In Infusion Rate Parameters
Minto et al, Anesthesiology, in press
14
Infusion rates should be reduced by 2/3s in the
elderly

• The infusion rate is decreased because of
  increased sensitivity and decreased clearance
• Adjusting the infusion rate for age is more
  important than adjusting it for weight

15
Age effects on infusion rate
Minto et al, Anesthesiology, in press
16
Age does not affect average time to emergence
17
Age affects variability in time to emergence
Minto et al, Anesthesiology, in press
18
Hemodynamics in Elderly

• Blood pressure may decrease 10-40 percent in
  elderly (gt70 yrs).
• Easily treated with ephedrine.
• May be associated with ST changes if patient has
  coronary artery disease.

19
Hemodynamics in Elderly

• Heart rate is usually stable but may increase
  abruptly on emergence.
• May be associated with ST changes if patient has
  coronary artery disease

20
Propofol/Alfentanil Interaction

• Adapted from Vuyk et al, Anesthesiology 838-22,
  1995
• Characterizes the concentrations for
• intubation
• maintenance
• on emergence
• Concentrations are 50 response level

21
Propofol/Opioid Technique
22
Propofol/OpioidTime to Awakening
23
Propofol/OpioidInfusion rates