Abstract SNACC-31

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Effect of Extracranial Blood Flow on Cerebral Oximetry: A Comparison of Three Cerebral Oximetry devices, NIRO-200NX, INVOS 5100S and TRS

Morishima K, Yoshitani K, Ohnishi Y
National Cerebral and Cardiovascular Center, Suita, Osaka, Japan

Cerebral oximetry using near-infrared spectroscopy (NIRS) is a noninvasive technique used to estimate regional cerebral oxygen saturation (rSO2). But, the quality of the measurements are uneven among the commercially available cerebral oximetry devices.
The absolute values of NIRS were unreliable. NIRS measurement could only report a change from baseline. NIRS values were affected by factors related to optical path length, such as hemoglobin concentration, the differential path length factor, skull thickness, and the area of cerebrospinal fluid layer (1). Recently, it is suggested that rSO2 measured by the three devices (INVOS 5100C [Covidien; Boulder, USA], FORE-SIGHT [CAS medical system Inc; Brand-ford, CT] and EQUANOX Classic 7600, [Nonin Medical Inc; Plymouth, MN]) is affected by the extracranial blood flow (2). However, other NIRS devices (NIRO-200NX and TRS-30 [Hamamatsu Photonix; Hamatsu, Japan]) have not been examined. The purpose of this study was to determine if NIRS guided rSO2 measurements from these cerebral oximeters, NIRO-200NX and TRS-30 are able to accurately account for extracranial contamination compared to INVOS-5100.
Fourteen healthy volunteers had three NIRS devices (INVOS 5100C, NIRO-200NX and TRS30) randomly applied to the forehead. After this, a circumferential pneumatic head cuff was positioned such that when inflated by MIZUHO MT880 Digital tourniquet (Mizuho Medical Innovation, Tokyo, Japan), hypoxia-ischemia would be produced in the extracranial scalp tissue beneath the NIRS cerebral oximeters. Cessation of blood flow to the extracranial tissue, and therefore induction of local scalp tissue hypoxia-ischemia was confirmed by a loss of forehead SpO2 (MAX FAST, Covidien, Boulder, USA) signal (fig1). Extracranial hypoxia was established, the head cuff remained inflated for 5 min, following this, the head cuff was deflated, allowing the superficial tissues to be re-perfused for 5 min. rSO2 and other physiologic measurements recorded every 1 min during 5 min of inflation and 5 min of deflation.

The induction of extracranial hypoxia-ischemia resulted in a significant reduction in rSO2 measurements by INVOS(66.1±9.1→56.3±9.5, p<0.001). But other two devices did not show significant changes, [NIRO200 (TOI: 64.9 ± 9.4→60.8 ± 9.5, p = 0.20), TRS30 (ScO2: 61.8 ± 8.1 → 58.9 ± 6.9, p = 0.12)] (fig2).

rSO2 measured by INVOS was influenced by extracranial contamination. This study indicated that the measurements of rSO2 by INVOS included the extracranial cerebral blood flow.

(1) Yoshitani K, Kawaguchi M, Miura N, et al. Anesthesiology. 2007 Mar;106(3):458-62
(2) Davie SN, Grocott HP. Anesthesiology. 2012 Apr;116(4):834-40.

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