Continuous Time-Domain Analysis of Cerebrovascular Autoregulation Using Near-Infrared Spectroscopy

Abstract

Background and Purpose-Assessment of autoregulation in the time domain is a promising monitoring method for actively optimizating cerebral perfusion pressure (CPP) in critically ill patients. The ability to detect loss of autoregulatory vasoreactivity to spontaneous fluctuations in CPP was tested with a new time-domain method that used near-infrared spectroscopic measurements of tissue oxyhemoglobin saturation in an infant animal model. Methods-Piglets were made progressively hypotensive over 4 to 5 hours by inflation of a balloon catheter in the inferior vena cava, and the breakpoint of autoregulation was determined using laser-Doppler flowmetry. The cerebral oximetry index (COx) was determined as a moving linear correlation coefficient between CPP and INVOS cerebral oximeter waveforms during 300-second periods. A laser-Doppler derived time-domain analysis of spontaneous autoregulation with the same parameters (LDx) was also determined. Results-An increase in the correlation coefficient between cerebral oximetry values and dynamic CPP fluctuations, indicative of a pressure-passive relationship, occurred when CPP was below the steady state autoregulatory breakpoint. This COx had 92% sensitivity (73% to 99%) and 63% specificity (48% to 76%) for detecting loss of autoregulation attributable to hypotension when COx was above a threshold of 0.36. The area under the receiver-operator characteristics curve for the COx was 0.89. COx correlated with LDx when values were sorted and averaged according to the CPP at which they were obtained (rϭ0.67). Conclusions-The COx is sensitive for loss of autoregulation attributable to hypotension and is a promising monitoring tool for determining optimal CPP for patients with acute brain injury.

Near-Infrared Spectroscopy can Monitor Dynamic Cerebral Autoregulation in Adults

“…With hemodynamic impairment, as in unilateral carotid obstruction, these phases were significantly changed reflecting disturbed autoregulation. The correlation between changes in cerebral perfusion pressure and a cerebral tissue oxygenation index over time was demonstrated to correlate with cerebral autoregulation assessed using laser Doppler cortical blood flow during experimental intracranial hypotension in piglets [7]. A similar technique proved to be promising in neonates [8].…”

“…Using the same principle, a moving correlation coefficient between 10 s averages of ABP and TOI signals (Tox) was calculated. A similar index, using the INVOS TM cerebral oxymeter, was validated in piglets using laser Doppler flowmetry and cerebral perfusion pressure measurements during graded hypotension experiments [7]. Values from the right and left hemisphere from TCD and NIRS were averaged for analysis.…”

Cerebral Autoregulation after Subarachnoid Hemorrhage: Comparison of Three Methods

“…Furthermore, THRT in prospective observational studies was shown to be useful in predicting clinical deterioration after SAH. 2,6 However, while clinical and experimental data exist supporting the validity of Sxa and TOxa, 13,23,25,31,32,34 neither index has been evaluated for its power to predict DCI. The mean flow index, Mx, which is derived from mean FV and CPP and its noninvasive version, Mxa, where ABP is used instead of CPP, have been previously investigated in patients with SAH.…”

“…(3) Near-infrared spectroscopy-based autoregulation, TOxa, was calculated as a moving, linear correlation coefficient between values of tissue oxygenation index and ABP from a 300-second window with an update every 10 seconds. [23][24][25] The minimum monitoring time required for results to be considered meaningful was 30 minutes.…”

“…Both TCD and near-infrared spectroscopy (NIRS) are modalities where the correlation coefficient method has been experimentally and clinically verified. [23][24][25] We have previously described in a prospective study that continuous indices of autoregulation (TCD and NIRS derived) are predictive of DCI. 9 However, the interrelationship between the two continuous indices as well as THRT has not been fully elucidated.…”