Validation Study of Covariates Model (VaSCoM) for Propofol
Status:
Completed
Trial end date:
2013-02-01
Target enrollment:
Participant gender:
Summary
Anaesthesia for surgical procedures can be provided using a continuous infusion of
intravenous drug. The most commonly used drug for this technique is propofol. Infusion
devices programmed with pharmacokinetic models can be used to infuse propofol to achieve a
target blood concentration. These pharmacokinetic models predict the rate of distribution of
propofol within the body and also the rate at which it is cleared. In practice, the
anaesthetist enters patient details such as age, sex and weight as well as a target blood
concentration of propofol. The infusion device then infuses propofol at the appropriate rate
to achieve this concentration.
White and colleagues recently published the Covariates Model for propofol. It is anticipated
that this model will have reduced bias and inaccuracy compared to the models in current
clinical use. The VaSCoM study has three objectives:
1. Prospective validation of the Covariates Model
2. Modelling of the effect site concentration of propofol
3. Comparison of propofol concentration in venous and arterial blood samples
To achieve the above objectives, patients over 18 years of age and undergoing elective
non-cardiac surgery will be recruited to the study. Anaesthesia will be delivered using a
target controlled infusion device programmed with the Covariates Model for propofol. The
target blood concentrations will be set according to a pre-determined schedule and all
measurements will be made prior to the start of surgery.
Prospective validation of the Covariates Model will be done by comparing blood concentration
of propofol predicted by the model to those actually measured. These results will then be
compared to the predictions made using the models in current clinical practice.
Modelling of the effect site means predicting the concentration of propofol in the brain for
a given blood concentration. This will involve using depth of anaesthesia monitors (such as
bispectral index) as surrogate markers of brain concentration and comparing this to the
predicted and measured blood concentrations of propofol.
Finally, important information on the distribution and clearance of propofol can be gained
through the comparison of venous and arterial blood samples. In this study, simultaneous
sampling of venous and arterial blood will facilitate this comparison.