Background and Objectives: Cerebral autoregulation (CA) may be assessed with the cerebral oximetry index (COx) correlating a surrogate marker of the cerebral blood flow (regional saturation of oxygen, rSO2) with either cerebral perfusion pressure (CPP) or arterial blood pressure (ABP) 1. An automated curve fitting method with specific software (ICM+®) calculates the “optimal ABP” (ABPOPT), defined as the ABP level where COx reaches its lowest value in an individual patient2.

Besides the technical challenges, we hypothesized that on-line monitoring of the COx index  in patients undergoing long neurosurgical procedures allows a retrospective definition of their intraoperative ABPOPT.

Measurements and Main Results: Retrospective analysis of prospectively collected data in the neurosurgical theatre at Hospital Clinic de Barcelona. 66 patients with continuous (> 2 hours) intraoperative monitoring of invasive ABP and rSO2  with ICM+® software were included.

COx was calculated online as the correlation between 10-second averaged values of rSO2  and mABP over a 300 s period (30 values). CA was considered intact for COx <0.3 and impaired for COx ≥ 0.3. ABPOPTcould be calculated in 49 (74%) of the 66 patients analyzed.  The relationship between the baseline ABP value at admission (ABPBV), ABPOPT and the average “real” intraoperative ABP (ABPR) in these patients was also studied.

Ten patients (20.41%) kept their average ABPR below 20% of their ABPBV. In 30 patients (61.22%) the average ABPR was lower than the ABPOPT.

Conclusion: On-line CA monitoring with non-invasive COx index is feasible and allows a retrospective calculation of the ABPOPT values in most of the patients of the study. The fact that ABPR was below calculated ABPOPT in a significant number of patients deserves further analysis.

References:

1.- Zweifel, C et al. Continuous assessment of cerebral autoregulation with near-infrared spectroscopy in adults after subarachnoid hemorrhage. Stroke, 2010; 41:1963-8

2.- Aries, MJH et al. Continuous determination of optimal cerebral perfusion pressure in traumatic brain injury. Critical Care Medicine, 2012; 40:2456-63



08 / Non-invasive intraoperative cerebral autoregulation: Monitoring and retrospective calculation of optimal arterial blood pressure in neurosurgical patients