Tissue oxygenation monitoring in the field: a new EMS vital sign

A tissue hemoglobin oxygen saturation (STO2) monitor was created to assess the perfusion status of a peripheral muscle bed using near infrared light to directly measure oxygen saturation in the microcirculation. Hypoperfusion has been noted when the STO2 is <75%. The use of this technology has not been tested in the prehospital setting. This pilot study was performed to assess the technology's ease of use in the field and to correlate STO2 readings with patient outcomes.

Hospital-based transport vehicles were equipped with STO2 monitors and personnel were asked to evaluate the functionality of the technology. Initial, average, and minimal STO2 values were collected and compared with data of the trauma registry.

Forty five of 55 surveys were returned with 100% reporting ease of use and no reports of interference with monitors or avionics. Monitoring length averaged 16.9 minutes +/- 6.9 minutes. Forty-one patients had complete data sets and five deaths were reported for a mortality rate of 12%. STO2 endpoints revealed and increased risk of death for every 10% decrease in STO2.

The STO2 monitor can easily be used in the prehospital environment. In addition, initial recordings were significantly different between survivors and nonsurvivors with every 10% decrease in STO2 increasing mortality threefold. This monitor seems to give the prehospital provider a noninvasive tool for assessment of hypoperfusion in the field and may allow for earlier resuscitative efforts to commence.