BACKGROUND: the benefits of monitoring cerebral blood flow (CBF) in stroke patients are apparent. New techniques combining near infrared spectroscopy (NIRS) and indocyanine green (ICG) dye dilution to estimate cerebral hemodynamics are available. However, with transcutaneous NIRS and optodes applied over the skin, the signal is contaminated by extracerebral tissues. The objective is to develop a new brain tissue probe for combined monitoring of intracranial pressure (ICP), CBF and cerebral blood volume (CBV).
METHODS: conventional intraparenchymal probes for ICP monitoring are supplied with optical fibers. The light is coupled into the brain tissue and collected after absorption and scattering with a light detector. Venous injections of 0.2 mg/kgbw ICG are performed. The mean transit time of ICG (mttICG), CBF and CBV are calculated.
RESULTS: with a prototype of the probe in a first patient with subarachnoid hemorrhage 6 pairs of repetitive measurements were performed. Mean values were for mttICG 5.6 ± 0.2 s, CBF 22.3 ± 2.8 ml/100 g/min and CBV 2.1 ± 0.3 ml/100 g.
CONCLUSIONS: NIR spectroscopy allows the synchronous determination of multiple parameters with one single device. By measurements in parallel with the NeMo Probe and NIRS optodes placed over the skin, new algorithms can be developed to subtract the extracerebral contamination from the NIRS signal.