Continuous time-domain analysis of cerebrovascular autoregulation using near-infrared spectroscopy.
OBJECTIVE
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.
Brady
Ken M
KM
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, USA. kbrady5@jhmi.edu
Lee
Jennifer K
JK
Kibler
Kathleen K
KK
Smielewski
Piotr
P
Czosnyka
Marek
M
Easley
R Blaine
RB
Koehler
Raymond C
RC
Shaffner
Donald H
DH
D000208:Acute Disease; D000367:Age Factors; D000818:Animals; D001930:Brain Injuries / Q000175:diagnosis / Q000503:physiopathology*; D002560:Cerebrovascular Circulation / Q000502:physiology*; D004195:Disease Models, Animal; D006706:Homeostasis / Q000502:physiology; D007022:Hypotension / Q000175:diagnosis / Q000503:physiopathology*; D017078:Laser-Doppler Flowmetry; D008991:Monitoring, Physiologic / Q000295:instrumentation* / Q000379:methods; D010092:Oximetry; D012680:Sensitivity and Specificity; D019265:Spectroscopy, Near-Infrared / Q000379:methods*; D013552:Swine