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(Stroke. 2007;38:2818.)
© 2007 American Heart Association, Inc.

Original Contributions

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

Ken M. Brady, MD; Jennifer K. Lee, MD; Kathleen K. Kibler, BS; Piotr Smielewski, PhD; Marek Czosnyka, PhD; R. Blaine Easley, MD; Raymond C. Koehler, PhD Donald H. Shaffner, MD

From the Department of Anesthesiology and Critical Care Medicine (K.M.B., J.K.L., K.K.K., R.B.E., R.C.K., D.H.S.), Johns Hopkins University School of Medicine, Baltimore, Md; and the Department of Academic Neurosurgery (P.S., M.C.), Addenbrooke’s Hospital, Cambridge, UK.

Correspondence to Ken Brady, MD, Johns Hopkins University School of Medicine, Department of Anesthesiology, Division of Pediatric Anesthesiology and Critical Care Medicine, 600 North Wolfe Street, Blalock 904, Baltimore, MD 21287. E-mail kbrady5{at}jhmi.edu

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 (r=0.67).

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.

Key Words: autoregulation • cerebral blood flow • hypotension • neonate • oxygenation • piglet

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