Near-infrared spectroscopy: A potential method for continuous, transcutaneous monitoring for compartmental syndrome in critically injured patients

Background: Near-infrared spectroscopy (NIRS) noninvasively measures tissue O-2 saturation (Sto(2)), and has been proposed as a means of monitoring fo r compartmental syndrome (CS). However, its specificity in hypoxemic, hypot ensive patients with severely reduced systemic oxygen delivery has not been tested. We hypothesized that NIRS can differentiate muscle ischemia caused by shock from ischemia caused by CS, Methods: Nine swine were anesthetized and an NIRS probe placed over the ant erolateral compartment of the hind leg, Compartment pressure was also measu red. A nerve stimulator was placed over the peroneal nerve, and CS was defi ned as loss of dorsiflexion twitch. At 30-minute sequential intervals, mean arterial blood pressure was reduced to 60% of baseline (phlebotomy), fract ion of inspired oxygen was reduced to 0.15, and compartment pressure was in creased in one limb by interstitial albumin infusion until CS occurred. Results: Hypotension combined with hypoxemia reduced Sto(2) from 82 +/- 4% to 66 +/- 10%, CS further reduced Sto(2) to 16 +/- 12% (p < 0.0001). During hypotension + hypoxemia + CS, control limb Sto(2) was 70 +/- 15% (p = 0.00 02 vs. experimental limb). Conclusion: NIRS detects muscle ischemia caused by CS despite severe hypote nsion and hypoxemia, making it potentially useful in critically injured, un stable patients.