University of Twente Student Theses


A combined BIS/NIRS sensor for detecting cerebrocortical oxygenation and activity in the ICU

Boers, T.G.W. and Durmus, N. and Lievestro, H.J. and Mulder, M.P. (2015) A combined BIS/NIRS sensor for detecting cerebrocortical oxygenation and activity in the ICU.

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Abstract:PROBLEM: Currently, the state of the brain is usually not measured in the Intensive Care Unit (ICU). Especially in dying patients, it is interesting to know when irreversible brain damage has occurred. Also, the progress of ischemia in the brain, the occurrence of irreversible damage and assurance about loss of consciousness are important to know. A small sensor is needed to provide a natural looking death of the patient to prevent the discomfort of relatives. BACKGROUND: Normally, the blood flow through the brain is kept constant using sophisticated autoregulatory mechanisms. When the cerebral perfusion pressure (CPP) becomes to low and therefore out of range for the autoregulation, ischemia will develop if the ability of increasing oxygen extraction is not enough to meet metabolic needs. If the ischemia persists, a cascade of events will ultimately lead to irreversible damage of the brain. DESIGN: The frontal cortex plays a crucial role in maintaining consciousness and is thus the preferred place to measure combined function and perfusion. The NIRS should measure the cerebral perfusion, at a depth of 20 mm. The spacing between light source and the detector should therefore be 40 mm. The BIS electrodes are all placed on positions of the international 10/20 sensor position system for EEG. Normally, the electrodes are placed at FPz, FP1, FT9 and AF7, but these positions may vary within the different designs during this study. EXPERIMENTS: The NIRS and BIS are combined into various designs, from which a top 4 is tested. A comparison is made besteen the different locations. Also they are tested for interdependent disturbances. The chosen designs are then further tested while performing interventions like the Valsalva maneuver and crash position. RESULTS: The lateral design has a lower average for both BIS and NIRS signals, than the frontal. Both the lateral designs has more fluctuating BIS data and show more signs of distortion. The NIRS signals of design A clearly increase or decline during the interventions, but no pattern is seen within the BIS data. CONCLUSION: The frontal design A, which is very similar to the original of the BIS and NIRS design, is chosen to be the best design. This model showed the least distortion, while delivering the best results during the intervention trials in which the oxygenation seems to be measured. Within this research, a combination of BIS and NIRS measurements did not show any correlations. RECOMMENDATIONS: With design A as a starting point, further research should primarily focus on the quality of the signal as captured by the sensor, eventually followed by the validation of the final design. A NIRS sensor with optical fibers is recommended to make smaller and more integrated designs. Also, it may be useful to consider using electrocardiography (ECG) electrodes instead of the BIS sensor. The disturbance should be measured on a phantom or dummy, to be certain that the two signals do not interfere with each other. In the future, other technique and applications may be studied as well.
Item Type:Essay (Bachelor)
Faculty:TNW: Science and Technology
Subject:44 medicine
Programme:Technical Medicine BSc (50033)
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