Main objective: blood pressure target to maintain cerebral perfusion is related to patient's
characteristics or comorbidities, it remains uncertain which threshold of blood pressure is
to use during general anesthesia in each specific case. Thus, it seems necessary to monitor
the cerebral perfusion during anesthesia and to determine the individual dynamic targets of
blood pressure. The measure of middle cerebral artery blood flow velocity by transcranial
doppler (TCD) is a clinical method to assess cerebral perfusion during general anesthesia and
several studies have reported the hemodynamic impact on cerebral blood flow during induction.
Cerebral perfusion can also be approached by near infrared spectroscopy (NIRS) which measures
continuously cerebral oxygen saturation. Bispectral index (BIS), which allows a simplified
form of continuous electroencephalogram monitoring to assess depth of anesthesia, could also
provide the cerebral hypoperfusion assessment quantified by the count of burst suppression
ratio (SR). Potentially, those tools need to be combined to assess cerebral perfusion
properly.
The goal of this study is to evaluate cerebral perfusion change in adult participants with or
without cardiovascular risk factors during a standardized propofol-remifentanil anesthesia
induction. Cerebral perfusion will be evaluated and compared using simultaneously the TCD,
NIRS and BIS measurements. Those measurements will be also repeated during and after
treatment of arterial hypotension episodes in both groups.
Population concerned : the study involves major patients who benefit from intraoperative
hemodynamic optimization with norepinephrine (as noradrenaline tartrate) for maintaining
blood pressure under general anesthesia during an interventional neuroradiology procedure or
orthopedic surgery.
Research Proceedings: all monitoring (TCD, BIS, NIRS) will be collected from the healthy
side, contralateral to the interventional side. BIS, NIRS and continuous non-invasive blood
pressure measurement will be all connected to the main monitor. For all participants, the
data from TCD, NIRS, BIS and the hemodynamic data will be collected over three distinct
periods of the interventional procedure : (1) baseline or during preoxygenation at FiO2 of
21% (fraction of inspired oxygen) in awake patients, (2) before Orotracheal Intubation and
(3) just after mechanical ventilation.
In patients presenting a hypotensive episode at any time of the procedure, all parameters
will be collected before and at the peak effect after a 10μg bolus injection of
norepinephrine.
Patients will be assigned to one of two groups according to the presence of cardiovascular
risk factors. Major risk factor is age > 50 years old. Minor risk factors include history of
congestive heart failure, history of cardiovascular event, current smoking, diabetes
mellitus, dyslipidemia, arterial hypertension. Patients will be classified into the high-risk
group (Hi-risk) if they have at least one major cardiovascular risk factor or two minor
factors, or into the low risk group (Lo-risk) if they present one minor or no risk factors.
During their interventional neuroradiology procedure or orthopedic surgery, all patients'
routine monitoring will consist in collecting the following parameters: electrocardiogram,
pulsated oxygen saturation, endtidal CO2, respiratory rate, tidal volume and neuromuscular
function.
For all patients whatever the comorbidities, anesthesia induction will be performed using a
target-controlled infusion (Orchestra® Base Primea - Fresenius Kabi France). According to our
standard of care, intra-operative episodes of hypotension (mean arterial pressure (MAP) < 65
mmHg or < 80% baseline) will be treated by Norepinephrine bolus of 10 μg.
Statistics: Changes in parameters across the time, during induction and/or during
vasopressors boluses will be tested by using a paired Student-t test after testing the
normality of the distribution. Correlation between the change in MAP and Vm during induction
will be done using Spearman test. Complete analysis will also be performed to compare the
Low-risk and High-risk patients. The analysis of vasopressor boluses will be performed
depending on the time of administration: boluses which are given immediately after induction
of anesthesia (early) and boluses given after a 30 minutes period of constant intravenous
calculated concentrations of anesthesia (late). All statistical analyses will be performed
using R statistical software (The 'R' Foundation for Statistical Computing, Vienna, Austria).
Results will be expressed as means (± SD). A two sided p value of 0.05 will be considered
significant.
The sample size calculation is based on the following assumptions: incidence of Hi-risk
patients of 50%, as previously reported; incidence of burst suppression during induction in
low risk patients of 20%; difference of incidence of burst suppression between low- and
high-risk patients of 30%; power at 80% and type I error at 5%. Accordingly, the calculated
sample size is 101 patients for the entire population.