Can near-infrared spectroscopy identify the severity of shock in trauma patients?

Background: Our recent experimental study showed that peripheral muscle tissue oxygen saturation (StO₂), determined noninvasively by near-infrared spectroscopy (NAS), was more reliable than systemic hemodynamics or invasive oxygenation variables as an index of traumatic shock. The purpose of this study was to establish the normal range of thenar muscle StO₂ in humans and the relationship between shock state and StO₂ in trauma patients. Methods: This was a prospective, nonrandomized, observational, descriptive study in normal human volunteers (n = 707) and patients admitted to the resuscitation area of our Level I trauma center (n = 150). To establish a normal StO₂ range, an NIRS probe was applied to the thenar eminence of volunteers (normals). Subsequently, in a group of trauma patients, an NIRS probe was applied to UK thenar eminence and data were collected and stored for offline analysis. StO₂ monitoring was performed continuously and noninvasively, and values were recorded at 2-minuie intervals. Five moribund trauma patients were excluded. Members of our trauma faculty, blinded to StO₂ values, classified each patient into one of four groups (no shock, mild shock, moderate shock, and severe shock) using conventional physiologic parameters. Results: Mean ± SD thenar StO₂ values for each group were as follows: normals, 87 ± 6% (n = 707); no shock, 83 ± 10% (n = 85); mild shock, 83 ± 10% (n = 19); moderate shock, 80 ± 12% (n = 14); and severe shock, 45 ± 26% (n = 14). The thenar StO₂ values clearly discriminated the normals or no shock patients and the patients with severe shock (p < 0.05). Conclusion: Decreased thenar muscle tissue oxygen saturation reflects the presence of severe hypoperfusion and near-infrared spectroscopy may be a novel method for rapidly and noninvasively assessing changes in tissue dysoxia.