Functional Near-infrared Spectroscopy in Unconscious Patients (fNIRS)

Severe ischemic and hemorrhagic stroke, as well cardiac arrest even after successful cardiopulmonary reanimation are great causes of morbidity and mortality in Europe and worldwide. Although prevention and therapy strategies, have been successfully improved during the past decades, the global stroke burden - measured in disability adjusted life years (DALY) - is still great.

Specifically, the improvements of intensive care treatments and neurosurgical procedures have lowered mortality rates, but simultaneously have increased survivors with severe disorder of consciousness (DoC) or persistent disabilities. As a result, an early prognosis in unconscious patients suffering from severe stroke in the intensive care unit (ICU) becomes more important for the clinician. An early reliable prognosis enables the clinician to empower the surrogates of an unconscious patient to make choices consistent with his preferences. It improves also overall patient management in the NICU and helps to identify an appropriate rehabilitation care. Since clinical assessment of comatose Patients is limited, other examinations are needed to enhance the reliability of a prognosis.

Evoked potentials, especially somatosensory and auditory evoked potentials (SSEP and AEP) are well established prognostic tools in unconscious ICU patients.

The advantage of evoked potentials over clinical assessments such as the Glasgow coma score (GCS) or laboratory values are that they are not influenced by intensive care interventions, and have a higher interrater reliability. They are also resistant to metabolic changes or sedation.

Electroencephalography (EEG) is another established prognostic tool in comatose patients. However, both, evoked potential and EEG are highly vulnerable to artefacts and expensive due to high workforce requirements.

Functional near-infrared spectroscopy (fNIRS) is a promising strictly non-invasive, bedside examination. It is based on the finding that infrared light is absorbed by oxygenated and deoxygenated haemoglobin. Brain activation can be measured with fNIRS due to an increase of oxygenated haemoglobin and decrease of deoxygenated haemoglobin. Different studies show that brain activation as a response to peripheral somatosensory and auditory stimulation as it is conducted in SSEP and AEP can be detected by fNIRS. Recent studies investigated also the use of fNIRS in unconscious patients. However, it is unknown whether and how the brain activation measured by fNIRS due to sensory stimulation correlates to the measurements of evoked potentials in unconscious patients and if it has any prognostic value in unconscious patients.

Therefore, the investigator aims to compare fNIRS with SSEP and AEP in unconscious neuro-intensive care patients suffering from severe hemorrhagic or ischemic stroke and in a control group with healthy conscious subjects. Hence, making it a potential prognostic tool for unconscious ICU patients.