Muscle Oxygenation as an Early Predictor of Shock Severity in Trauma Patients

We evaluated the potential utility of a new prototype noninvasive muscle oxygenation (MOx) measurement for the identification of shock severity in a population of patients admitted to the trauma resuscitation rooms of a Level I regional trauma center. The goal of this project was to correlate MOx with shock severity as defined by standard measures of shock: systolic blood pressure, heart rate, and lactate.

Optical spectra were collected from subjects by placement of a custom-designed optical probe over the first dorsal interosseous muscles on the back of the hand. Spectra were acquired from trauma patients as soon as possible upon admission to the trauma resuscitation room. Patients with any injury were eligible for study. MOx was determined from the collected optical spectra with a multiwavelength analysis that used both visible and near-infrared regions of light. Shock severity was determined in each patient by a scoring system based on combined degrees of hypotension, tachycardia, and lactate. MOx values of patients in each shock severity group (mild, moderate, and severe) were compared using two-sample t tests.

In 17 healthy control patients, the mean MOx value was 91.0 ± 5.5%. A total of 69 trauma patients were studied. Patients classified as having mild shock had a mean MOx of 62.5 ± 26.2% (n = 33), those classified as in moderate shock had a mean MOx of 56.9 ± 26.9% (n = 25) and those classified as in severe shock had a MOx of 31.0 ± 17.1% (n = 11). Mean MOx for each of these groups was statistically different from the healthy control group (P < 0.05).Receiver operating characteristic analyses show that MOx and shock index (heart rate/systolic blood pressure) identified shock similarly well (area under the curves [AUC] = 0.857 and 0.828, respectively). However, MOx identified mild shock better than shock index in the same group of patients (AUC = 0.782 and 0.671, respectively).

The results obtained from this pilot study indicate that MOx correlates with shock severity in a population of trauma patients. Noninvasive and continuous MOx holds promise to aid in patient triage and to evaluate patient condition throughout the course of resuscitation.