Preliminary Results
Farid
Garoud, Pierre-Yves Leuquueux, Gilbert Bejjani, Luc Barvais
Free
University of Bruxelles, Bruxelles
Background
and Goal of Study
Pharmacodynamic
(PD) models of propofol are usually described as a first order process with one
equilibration rate constant (Ke0) and two compartments (plasma and
effect-site)1. With various results, several studies suggested that propofol PD
could not be a first order process2,3. The time to peak effect of propofol is a
model independent parameter which is known not to vary with the dose, when given
as a bolus1. But this assertion is valid only if the PD of propofol is a first
order process. The present study measures the time to peak effect of propofol
with 2 different bolus doses.
Materials
and Methods
After
approval of local ethical committee and informed and written consent, 16 ASA
I/II patients aged less than 50 were randomly assigned to 2 groups in a blinded
manner to receive a bolus dose of propofol of either 1 mg/kg (group A) or 3
mg/kg (group B). BIS (Aspect Medical Systems, Nattick,MA) was recorded every 2
seconds and the time between the propofol bolus and the lowest BIS value minus
10 seconds (mean time for BIS processing) was considered as the time to peak
effect.
Results
and Discussions
There
was no significant difference between group A and B regarding age (41 ± 6 vs 35
± 8 yr respectively), sex (2 males and 6 females in both groups), weight (67 ±
16 vs 68 ± 20 kg) and height (163 ± 9 vs 168 ± 13 cm).
As
expected, the minimum BIS value was significantly lower after a bolus dose of
propofol of 3 mg/kg (17 ± 10) than after a dose of 1 mg/kg (47 ± 13)
(p<0.05), but this value was obtained significantly later (113 ± 41 sec vs
78 ± 14 sec : p<0.05). This observation cannot be described with a direct PD
model. (Values are mean ± SD).
Conclusion(s)
The
time to peak effect of propofol varies with the bolus dose suggesting that the
PD of propofol may not be a first order process and that the research into a new
indirect PD model should be considered.
References
1.
Minto CF et al. Anesthesiology 2003; 99:324-33
2.
Stokes DN, Hutton P. Anesth Analg 1991; 74:316-7
3.
Doufas AG et al. Anesthesiology 2004; 101:1112-21