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| The UK Society for Intravenous Anaesthesia |
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Glasgow Meeting - May 2003 Comparison of effect-site propofol concentrations at loss of consciousness and recoveryOlinga A., Ousmanou B., *Cantraine F., * Coussaert E., Barvais L. Departments of Anesthesiology and *Scientific Computing, Free University of Brussels.Background: Loss of consciousness (LOC) has been related more to the concentration of propofol at the effect site (Ce) rather than in the plasma (Cp) when target controlled infusion (TCI) of propofol was delivered 1. It was also demonstrated that LOC was markedly dependent on the value of keo included in the pharmacokinetic set 2. Our purpose was to study if there was a relation between propofol Ce at LOC and during the recovery period when a population pharmacokinetic-pharmacodynamic set of propofol was used 3. During both periods, remifentanil Ce was targeted at the same level using the pharmacokinetic set of Minto et al 4 which has been associated with an acceptable predictive accuracy. Materials and methods: After local ethical committee approval and informed consent, 20 adult ASA I-II patients scheduled for elective minor surgery were studied. All patients were premedicated with alprazolam 0.5 mg orally. After having targeted a remifentanil Ce at 1 ng/ml, propofol Ce was progressively increased by steps of 1 µg/ml until LOC was obtained. Patients were asked to respond to a simple verbal order (eye opening) every 15 seconds. During surgery, propofol was maintained at the level of Ce recorded at LOC and remifentanil Ce was adjusted according to the intensity of the surgical stimulation. At the end of surgery, remifentanil was decreased and targeted at 1 ng/ml again. Thereafter, propofol TCI was stopped. During the awakening period, patients were tested every 15 seconds and propofol Ce were recorded at tracheal extubation and eyes opening. The t-paired test was used to compare propofol Ce at LOC and during the recovery period. Probability values less than 0.05 were considered as statistically significant. Results are expressed as mean ± SD. Results :
The
evolution of propofol Ce (µg/ml) at LOC, extubation and eyes opening is
depicted for each patient in the figure and demographics is shown in the table.
Using the set of Schnider et al 3, propofol Ce is
significantly higher at LOC (3.2 ± 0.8 µg/ml) than at eyes opening (1.4 ± 0.5
µg/ml) (p<0.01). Patients with
high or low propofol Ce at LOC were awake at high or low propofol Ce,
respectively.
Discussion and conclusion In
young adult healthy patients undergoing minor surgery, the calculated propofol
Ce at recovery, using the set of Schnider et al 3, are always less
than the propofol Ce observed at LOC when similar level of remifentanil
analgesia is targeted. This
difference could partially be explained by either a positive bias of the set of
Schnider in our study conditions or by a slower return of propofol from the
effect-site to the plasma. During
effect-site propofol and remifentanil TCI, the targeted propofol Ce at awakening
could be extrapolated by halving propofol Ce at LOC when remifentanil Ce are at
the same level. References:1.
Anesthesiology 1999; 90: 92-7
2.
Anesthesiology 2000; 92: 399-406.
3.
Anesthesiology 1999; 90: 1502-16.
4.
Anesthesiology 1997; 86: 10-23.
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