An evaluation of the normal range of StO2 measurements at rest and following a mixed exercise protocol

Key messages Normal StO₂ values at rest have a wide range, falling typically between 46-95%.

StO₂ measurements recorded from different anatomical sites have a broad overlap, but have significantly different distributions and mean values.

Exercise is associated with a statistically significant increase in StO₂ values which persists for at least 10 minutes into the recovery period.

Introduction

Near infrared spectroscopy (NIRS) is an emerging technique in medical practice which allows real time, non-invasive determination of local tissue oxygenation (StO₂ , expressed as a percentage). Although sharing similarities with pulse oximetry used to measure arterial oxygen saturation (SpO₂ ), SpO₂ and StO₂ are fundamentally different physiological measurements. SpO₂ is a global measurement, which under most circumstances should be broadly similar in all arterial circulations in the body. StO₂ is a local measurement of tissue arterial and venous oxygenation and will demonstrate regional variations based upon local physiology.

NIRS has several applications relevant to military clinical practice: the diagnosis of acute or chronic exertional compartment syndrome, 1 2 assessment of tissue viability and early recognition of free/regional reconstructive flap failure 3-5 and guiding resuscitation in trauma or sepsis management. 6-8

To interpret the results of NIRS measurements from experimental studies and in clinical practice, it is necessary to have a working knowledge of the normal range of StO₂ . Unfortunately, despite a large body of ongoing work in the field, to date there has only been one published description of the range of normal StO₂ values. Crookes et al 6 described StO₂ measurements recorded from the thenar eminence, using an InSpectra Tissue Spectrometer (Hutchinson Technology, Hutchinson, Minnesota, USA) in an unselected population found on a university campus. Their study demonstrated a wide range of normal values, with a skew left distribution ( Figure 1 ) and statistically significant differences in the mean StO ₂ between men and women, smokers and non-smokers, and different ethnic groups. Although these data have often been cited as a reference range by other researchers studying different anatomical locations, there is no evidence to support the assumption that StO ₂ values are identical between sites. Furthermore, these data may not be applicable to a military population.

In military and civilian...