Slow vasogenic fluctuations of intracranial pressure and cerebral near infrared spectroscopy-an observational study

Increased slow-wave activity in intracranial pressure (ICP) signifies an exhausted cerebrospinal compensatory reserve across a range of conditions. In this study, we attempted to describe synchronisation between slow waves of ICP and of near-infrared spectroscopy (NIRS) variables during controlled elevation of ICP. Nineteen patients presenting with symptomatic hydrocephalus underwent a Computerised Infusion Test. NIRS-derived indices, ICP and arterial blood pressure (ABP) were recorded simultaneously. ICP increased from 9.3 (6.0) mmHg to a 17.1 (8.9) mmHg during infusion. Slow waves in ICP were accompanied by concurrent waves in each NIRS variable (including deoxygenated haemoglobin (Hb) and oxygenated haemoglobin (HbO2)) with a mean coherence of > 0.7 and no significant phase shift. In the same bandwidth (0.3-1.8 min(-1)), ABP fluctuations occurred with a coherence of 0.77 and phase lead of 40A degrees with respect to ICP. The power of ICP slow waves increased significantly during infusion plateau with a corresponding increase in power of Hb waves. Slow fluctuations in cerebral oximetry as detected by NIRS coincide with and are implicated in the origin of ICP slow waves and increases during periods of exhausted cerebrospinal compensatory reserve. NIRS may be used as a non-invasive marker of increased ICP slow waves (and therefore reduced CSF compensatory reserve).