Noninvasive autoregulation monitoring with and without intracranial pressure in the naive piglet brain.
BACKGROUND
Cerebrovascular autoregulation monitoring is often desirable for critically ill patients in whom intracranial pressure (ICP) is not measured directly. Without ICP, arterial blood pressure (ABP) is a substitute for cerebral perfusion pressure (CPP) to gauge the constraint of cerebral blood flow across pressure changes. We compared the use of ABP versus CPP to measure autoregulation in a piglet model of arterial hypotension.


METHODS
Our database of neonatal piglet (5-7 days old) experiments was queried for animals with naïve ICP that were made lethally hypotensive to determine the lower limit of autoregulation (LLA). Twenty-five piglets were identified, each with continuous recordings of ICP, regional cerebral oximetry (rSo2), and cortical red cell flux (laser Doppler). Autoregulation was assessed with the cerebral oximetry index (COx) in 2 ways: linear correlation between ABP and rSo2 (COx(ABP)) and between CPP and rSo2 (COx(CPP)). The lower limits of autoregulation were determined from plots of red cell flux versus ABP. Averaged values of COx(ABP) and COx(CPP) from 5 mm Hg ABP bins were used to show receiver operating characteristics for the 2 methods.


RESULTS
COx(ABP) and COx(CPP) yielded identical receiver operating characteristic curve areas of 0.91 (95% confidence interval [CI], 0.88-0.95) for determining the LLA. However, the thresholds for the 2 methods differed: a threshold COx(ABP) of 0.5 was 89% sensitive (95% CI, 81%-94%) and 81% specific (95% CI, 73%-88%) for detecting ABP below the LLA. A threshold COx(CPP) of 0.42 gave the same 89% sensitivity (95% CI, 81%-94%) with 77% specificity (95% CI, 69%-84%).


CONCLUSIONS
The use of ABP instead of CPP for autoregulation monitoring in the naïve brain with COx results in a higher threshold value to discriminate ABP above from ABP below the LLA. However, accuracy was similar with the 2 methods. These findings support and refine the use of near-infrared spectroscopy to monitor autoregulation in patients without ICP monitors.
Department of Anesthesiology, Division of Pediatric Anesthesiology and Critical Care Medicine, The Johns Hopkins University School of Medicine, 600 North Wolfe St., Blalock 943, Baltimore, MD 21287, USA. Kbrady5@jhmi.edu
Ken M
KM
Brady
Jennifer O
JO
Mytar
Kathleen K
KK
Kibler
Charles W
CW
Hogue
Jennifer K
JK
Lee
Marek
M
Czosnyka
Peter
P
Smielewski
R Blaine
RB
Easley
D000818:Animals; D001794:Blood Pressure / Q000502:physiology; D001921:Brain / Q000502:physiology*; D002404:Catheterization; D002560:Cerebrovascular Circulation / Q000502:physiology; D003627:Data Interpretation, Statistical; D006706:Homeostasis / Q000502:physiology*; D007427:Intracranial Pressure / Q000502:physiology*; D016013:Likelihood Functions; D016014:Linear Models; D008991:Monitoring, Physiologic / Q000379:methods*; D010092:Oximetry; D010100:Oxygen / Q000097:blood; D012372:ROC Curve; D013552:Swine
D010100:Oxygen