Oxygen saturation determined from the mouth is an early indicator of central hypovolemia in humans

Introduction

Studies have suggested that tissue oxygenation (StO₂) measured on the thenar muscle is not sensitive to track acute changes in hemodynamics due to reductions in central blood volume. We aimed to investigate the feasibility of StO₂ measurements in the mouth as a quantitative indicator comparable with StO₂ measurements obtained from the thenar eminence during changes in central blood volume (CBV).

Methods

We performed a head-up tilt (HUT) test in 10 healthy volunteers as an experimental model to reduce CBV. StO₂ was continuously measured using two devices (InSpectra model 650): a multiple depth optical probe was placed over the thenar eminence (15 and 25 mm) and a 1-mm probe was placed in the mouth. Subjects were placed on an electrically driven tilt table with a footboard. After 5 minute baseline measurements in the supine position, the table was tilted up to 70° and returned to the supine position after 10 minutes. StO₂ readings were analyzed at the lowest stroke volume value.

Results

All subjects (mean age: 23 ± 6; six males) tolerated well the supine and head-up positions. Cardiac output significantly decreased in the HUT position; simultaneous decrease in StO₂ was observed in the mouth, but not in the thenar. The general results of the HUT test are shown in Tables 1 and 2.

Table 1 Hemodynamics in the baseline and in the head-up tilt (HUT)

Table 2 StO₂ in the baseline and in the head-up tilt (HUT)

Conclusions

Near-infrared spectroscopy can be used in the mouth to track changes in central blood volume. Our results showed that buccal StO₂ is an earlier indicator of acute hemodynamic responses to the HUT-induced central hypovolemia than thenar StO₂.