Non-invasive Measurement of Arterial Stiffness

Reducing the risk of perioperative cardiovascular complications is a major issue for anesthesiology practice and research. The risk of postoperative cardiovascular complications could therefore be stratified by screening "rigid" patients who have no cardiovascular risk factors.

Assessment of large-caliber artery stiffness is a predictive, early, and independent biomarker of cardiovascular events, currently included in European guidelines for the management of hypertension. It is also a physiological parameter that reflects left ventricular afterload and is very useful during the management of patients under general anesthesia. The parameter considered as the "gold standard" for the evaluation of this arterial stiffness is the measurement of the pulse wave velocity (PWV) or carotid-femoral pulse wave velocity (PWVcf). PWVcf is the propagation speed of the pulse wave from the carotid artery to the femoral artery, i.e., the time it takes for the pulse wave to travel from a point in the carotid artery to a point in the femoral artery. PWVcf has not become widespread in routine clinical practice because of the complexity of the measurement method. Indeed, PWVcf measurement can only be performed by imaging (MRI), or by ultrasound technique (combined carotid and femoral Doppler) or by combined tonometry (e.g. SphygmoCor, Complior). These techniques require specific equipment as well as training, expertise and learning of the collection technique. Previous studies have allowed the development of an algorithm allowing indirect measurement of PWV from combined carotid-femoral Doppler and tonometry PWVcf measurements in patients under general anesthesia. Thanks to the acquisition tools, the data will be available and of high quality, guaranteeing that the tools/algorithm developed from them will not be biased and will be more efficient.

The objective of this study is to validate, during anesthesia, the method of estimation of PWV (obtained using the usual monitoring tools including the parameters derived from the SpO2 signal, NIBP and ECG) by comparing it to the reference method by measuring the carotid-femoral transit time obtained by Doppler effect.

Patients over 18 years old are eligible to participate in this protocol. During the anaesthesia consultation, patients will be given a letter of information on the objectives and progress of the study. Their non-objection to participate in this study will be collected at the latest during the pre-anesthetic visit, the day before the operation, after a period of reflection.

The protocol will start on the day of the operation. The procedures will be performed under general anesthesia or locoregional anesthesia. The protocol does not interact with the care procedure.

The 2 self-adhesive Doppler sensors are placed at the level of the common carotid and superficial femoral arteries at the level of the Scarpa. The visualized signal is automatically validated after several cycles when the quality is satisfactory (Athys Medical©) - WAKIe R3 2TC®). This signal, allowing the measurement of the carotid-femoral transit time, is then recorded on Data Warehouse Connect.

The distance between the two measurement points is measured with a tape measure. Knowing the carotid-femoral transit time, the propagation speed of the wave (expressed in m/s) can be calculated.

No invasive devices are used in addition to those required for anesthesia. All the monitoring instruments described above, except the one studied, are already used routinely in our department. The duration of anesthesia is not prolonged for the study. The Doppler is performed during the awake, anesthetic induction and awake phase.

No additional exams will be performed. The anesthetic strategy is decided by the anesthesiologist in charge of the operation.

The physician in charge of the study collecting the data does not participate at any time in the management of the patient. The measures cannot influence the prescribing physician since at this stage the data are not yet analyzed and available

The estimation of the number of subjects to be included is based on the primary endpoint, namely the intraclass correlation coefficient. Thus, to demonstrate an ICC of 0.9 with a confidence interval of 0.1, for a 5% alpha risk, it is necessary to include 98 patients.

Continuous data are expressed as median [interquartile] and categorical data as n (%). Categorical variables will be compared by Mann-Whtney test and continuous variables by Wilcoxon test.

The agreement between the two methods will be evaluated by the intra-class correlation coefficient as well as by the Bland-Altman representation (with determination of the bias and the limits of agreement), for the different parameters of interest. All statistical analyses will be performed using R statistical software (The 'R' Foundation for Statistical Computing, Vienna, Austria). The results will be expressed as means (± standard deviation). A p-value less than 0.05 is considered significant