Is mean blood saturation a useful marker of tissue oxygenation?

Abstract

Thorn CE, Matcher SJ, Meglinski IV, Shore AC. Is mean blood saturation a useful marker of tissue oxygenation?. Am J Physiol Heart Circ Physiol 296: H1289 -H1295, 2009. First published March 13, 2009 doi:10.1152/ajpheart.01192.2008.-Increasingly we are monitoring the distribution of oxygen through the microcirculation using optical techniques such as optical reflectance spectroscopy (ORS) and near-infrared spectroscopy. Mean blood oxygen saturation (SmbO2) and tissue oxygenation index measured by these two techniques, respectively, evoke a concept of the measurement of oxygen delivery to tissue. This study aims to establish whether SmbO2 is an appropriate indicator of tissue oxygenation. Spontaneous fluctuations in SmbO2 observed as changes in concentration of oxyhemoglobin ([HbO2]) and deoxyhemoglobin ([Hb]) were measured by ORS in the skin microcirculation of 30 healthy subjects (15 men, age 21-42 yr). Fourier analysis identified two distinctly different spontaneous falls in SmbO2. The first type of swing, thought to be induced by fluctuations in arterial blood volume, resulted from the effects of respiration, endothelial, sympathetic, and myogenic activity. There was no apparent change in [Hb]. In contrast, a second type of swing resulted from a fall in [HbO2] accompanied by a rise in [Hb] and was only induced by endothelial and sympathetic activity. Thus the same fall in SmbO2 can be induced by two distinct responses. A "type I" swing does not suggest an inadequacy in oxygen delivery whereas a "type II" swing may indicate a change in oxygen delivery from blood to tissue. SmbO2 alone cannot therefore be accepted as a definitive marker of tissue oxygenation.optical reflectance spectroscopy; microcirculation THE EXQUISITE STRUCTURE OF the microcirculation is designed to deliver nutrients to every cell in the human body. The development over the last 30 years of noninvasive optical techniques such as optical reflectance spectroscopy (ORS) (2,18,22,33) and near-infrared spectroscopy (NIRS) (7, 23) has significantly advanced our understanding of the hemodynamics of the cutaneous (1, 20), muscle (36), cerebral (11,13,29,48), and gastrointestinal (15, 38) microcirculation. Furthermore, mean blood saturation (S mb O 2 ) and tissue oxygen index (TOI) derived by ORS and NIRS, respectively, evoke a concept that we can also measure the oxygen delivery to the tissue. These parameters are increasingly being identified as indicators of tissue hypoxia (1,3,8,15,21,28,34,47), which is a common end product of circulatory shock and a primary target for resuscitation efforts (5, 37).The primary goal of this study was to establish whether cutaneous tissue oxygen saturation (i.e., S mb O 2 ) derived by ORS is an appropriate indicator of tissue oxygenation. A further goal was to explore differences in S mb O 2 across cuta- [Hb] across all the vessels of the microcirculation of the skin. Therefore the derived S mb O 2 is a mean blood oxygen saturation across arterioles, capillaries, and venules. METHODS ORS.The ORS instrumentatio...

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