on August 30, 2007
Published online before print August 30, 2007, doi: 10.1161/STROKEAHA.107.485706
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Submitted on March 8, 2007
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. * To whom correspondence should be addressed. 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.
Revised on April 2, 2007
Accepted on April 5, 2007
Continuous Time-Domain Analysis of Cerebrovascular Autoregulation Using Near-Infrared Spectroscopy
Ken M. Brady MD*;
Key words: autoregulation • cerebral blood flow • hypotension • neonate • oxygenation • piglet
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