gms | German Medical Science

Objective: Monitoring of cerebrovascular pressure reactivity (PRx) has diagnostic and prognostic value in head injured patients but needs invasive monitoring of intracranial pressure (ICP). Near infrared spectroscopy (NIRS) is a non-invasive modality, suitable for the continuous detection of cerebral blood volume changes that are reflected by the Total Hemoglobin Index. To compare a NIRS-based index, total hemoglobin reactivity (THx), against standard measurements of PRx.

Methods: Forty patients with closed head injury were prospectively included in the study from June 2008 to June 2009. Patients were monitored daily with arterial blood pressure (ABP), ICP and Total Hemoglobin Index. PRx and THx were calculated as the moving correlation coefficients, using 5 minute time-windows, between 10-second averaged values of ICP and ABP, and Total Hemoglobin Index and ABP, respectively. By evaluation of the distribution of PRx and THx versus cerebral perfusion pressure (CPP) and ABP, so called ‘optimal' CPP and ‘optimal' ABP was calculated, indicating pressures levels where both indices demonstrated strongest reactivity (I.e. PRx and THx reached minimal values).

Results: 120 recordings on individual days were performed, with a median time of the first day after head injury (IQR 0.75–2), and stopped at day 4 (IQR 2–6), with a total duration of 1,760 hours. PRx and THx demonstrated significant association in averaged individual recordings (r=0.49 p<0.0001) and averaged for patients (r=0.56, p=0.0002). Assessment of optimal CPP and ABP using THx was possible in about 50% of recordings and showed a good agreement with the optimal CPP and ABP assessed with PRx.

Conclusions: THx, noninvasively assessed with NIRS, significantly correlated with PRx. THx may be of diagnostic value to optimize a cerebrovascular reactivity- oriented therapy, especially in patients for whom direct ICP monitoring is not feasible.