Brain metabolic changes during awake and asleep craniotomy measured by cortical microdialysis

Patients undergoing brain surgery are anaesthetized by general anesthetics that
induce hypnosis and analgesia. During anesthesia the metabolism of the brain
alters, thereby contributing to the unconscious state of the patient. In
particular, lowering of brain metabolism during anesthesia may support
perioperative brain protection against stimuli such as ischemia and the
production of reactive oxygen species. Currently, there are only limited
reports available regarding the direct effects of anesthetics on brain
metabolism. Such brain metabolic alterations have never been associated with
patient level of consciousness. The present project focuses on the direct
measurement of metabolic alterations in the subcortex of the brain during an
awake state and under anesthesia in patients undergoing craniotomy during a
so-called asleep-awake-asleep procedure. These direct measurements will be
performed by microdialysis of interstitial brain fluids during surgery. We
expect to confirm that anesthesia leads to alterations in brain metabolism
compared to an awake state. In particular, metabolites as glutamate, glucose
and lactate will increase due to reduced brain perfusion. In contrast, we
expect lower levels of pyruvate and glycerol during anesthesia.

Does anesthesia itself or transition of anesthesia to an awake state and vice
versa lead to changes in the lactate/pyruvate ratio, glucose, glycerol and
glutamate concentration as measured in the brain interstitial fluid?
Are the metabolic alterations during anesthesia and full consciousness
different in healthy or diseased brain areas (e.g. tumor tissue)?

Open, prospective, observational trial

The present study has a scientific merit and will not result in patient
benefits. In general, the burden and risks associated with the present study
are minimal. The catheters, needed for the measurements will be placed in
tissue that will be subsequently removed during the operation. Therefore, there
is no additional risk for brain tissue damage. With microdialysis, 144 µl of
interstitial brain fluid metabolites will be sampled in the region surrounding
the catheter. This will not disrupt the metabolic state in surrounding healthy
tissue. Sampling can take place simultaneously during the normal operative
procedure. It will therefore not delay or interrupt the treatment. All
measurements will be stopped before the end of the operation.
Furthermore, blood sampling will be drawn from an arterial line that is placed
preoperatively on a routine basis. Blood sampling will therefore not add up to
patient discomfort. The total volume of blood that will be drawn is 10 x 10=
100 ml. Blood samples will be drawn from an existing arterial line, and will
therefore not add up to patient discomfort.