Measuring static and dynamic cerebral autoregulation intraoperatively in volunteers at different steady-state MBP.

Cerebral autoregulation (CA) is the physiological mechanism that maintains
cerebral blood flow (CBF) more or less constant despite variations in blood
pressure and therefore safeguards cerebral metabolic needs during hypotension.
This implies that cerebral vessels dilate during hypotension (directing blood
flow towards the brain) and constrict during hypertension (protecting the brain
for hyperperfusion). Thus, if the efficacy of CA is compromised, the risk of
cerebral hypoperfusion increases when blood pressure is low, for example during
anaesthesia.
To quantify the integrity of CA is challenging since simultaneous blood
pressure and CBF measurements are required across a wide range of blood
pressures Determination of blood pressure is simple but gold standard
quantification of CBF is highly invasive and time consuming.

The development new techniques such as finger photoplethysmography and the
transcranial Doppler enabled non-invasive, real-time, recording of systemic
blood pressure and blood flow velocity (V) in the middle cerebral artery (MCA).
This simplified the measurements on CA considerably. Furthermore, the concept
of dynamic CA was introduced. Contrary to static CA, this describes how quickly
the cerebral vessels react to a change in blood pressure to normalise CBF

In this proposal, we aim to clarify the (limits of) CA in the
non-cardiothoracic surgical population. To study this, we monitor brain
perfusion indices and blood pressure (both non-invasively) in a cohort of
patients under general anaesthesia.

We aim to record brain perfusion indices at MAP 60, 70, 80, 90 and 100 mmHg.
The value of MAP 60 mmHg is the accepted lower limit during anaesthesia and MAP
100 mmHg corresponds to the normal awake value (RR 120/80). Therefore, all
these values are within the normal physiological range. To correct for
different anaesthesia regimens, we randomise patients to receive either
inhalational or intravenous anaesthesia. Both techniques are accepted ways of
administering general anaesthesia and are both employed on a daily basis in our
hospital (depending on the preference of the anaesthesiologist).

Establish relationship between static and dynamic CA during general intravenous
or inhalational anaesthesia.

We propose a single centre, open label trial in ASA-I or II intraoperative
patients. Patients will be recruited from the elective operating schedule.
After induction of anaesthesia, we perform measurements on cerebral perfusion.
After data collection, the study is terminated intraoperatively. There will be
no follow-up postoperatively.

Test subjects will be investigated while undergoing planned surgery. The entire
investigation will take place while under anaesthesia. This means the test
subjects will not experience significant extra burden from the test
measurements. Conversely, they will not have additional benefits from the
investigation.