Near Infrared Spectroscopy as Possible Non-invasive Monitor of Slow Vasogenic ICP Waves
We aimed to study synchronisation between ICP and near infrared spectroscopy (NIRS) variables induced by vasogenic waves of ICP during an infusion study in hydrocephalic patients and after TBI. Nineteen patients presenting with hydrocephalus underwent a diagnostic intraventricular constant-flow infusion test. The original concept of the methodology, presented in the current paper, was derived from this material. Then the method was applied in 40 TBI patients, with results reported in an observational manner. During monitoring, NIRS deoxygenated and oxygenated haemoglobin (Hb, HbO2) were recorded simultaneously with ICP. Moving correlation coefficient (6 min) between Hb and HbO2 was tested as a marker of the slow vasogenic waves of ICP.
During infusion studies ICP increased from 10.7 (5.1) mmHg to a plateau of 18.9 (7.6) mmHg, which was associated with an increase in the power of slow ICP waves (p = 0.000017). Fluctuations of Hb and HbO2 at baseline negatively correlated with each other, but switched to high positive values during periods of increased ICP slow-wave activity during infusion (p < 0.001). Similar behaviour was observed in TBI patients: baseline negative Hb/HbO2 correlation changed to positive values during peaks of ICP of vasogenic nature.
Correlating changes in Hb and HbO2 may be of use as a method of non-invasive detection of vasogenic ICP waves.
KeywordsNear infrared spectroscopy Intracranial pressure Infusion test Traumatic brain injury
The project was supported by the National Institute of Health Research, Biomedical Research Centre, Cambridge University Hospital Foundation Trust – Neurosciences Theme plus Senior Investigator Award (JDP) and Foundation for Polish Science (MK).
Conflict of interest statement
ICM + software (www.neurosurg.cam.ac.uk/icmplus) is licensed by the University of Cambridge, Cambridge Enterprise Ltd. PS and MC have a financial interest in a part of the licensing fee. CZ received a travel grant from Hamamatsu Photonics, Welwyn Garden City, Hertfordshire, UK.