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A Wireless Intramuscular Near-infrared Spectroscopy Device Detects Muscle Oxygenation Changes In Porcine Model Of Lower Extremity Compartment Syndrome
Amanda Westman, PhD1, Hexia Guo, MS2, Yameng Xu, MS1, Wubin Bai, PhD3, Wei Ouyang, PhD2, William Moritz, MD1, Lauren Jacobson, MD1, Yang Weng, MS2, Hao Zang, MS2, Changsheng Wu, PhD2, Ziying Hu, PhD2, Shuo Li, PhD2, Di Lu, PhD2, Hany Arafa, MS2, Matthew MacEwan, MD PhD1, Lauren Tatman, MD1, John Rogers, PhD2, Mitchell Pet, MD1.
1Washington University in St. Louis, St. Louis, MO, USA, 2Northwestern University, Evanston, IL, USA, 3University of North Carolina Chapel Hill, Chapel Hill, NC, USA.

PURPOSE: Direct measurement of intracompartmental pressure (ICP) and serial examination are the primary strategies for the detection of CS; however, these strategies are operator dependent and yield information that only indirectly reflects intracompartmental muscle perfusion. As a result, instances of unnecessary fasciotomy and unrecognized compartment syndrome are relatively common. Recently, near-infrared spectroscopy (NIRS)-based systems for compartment monitoring have generated interest as an adjunct tool. NIRS directly measures the oxygenation of intracompartmental muscle (StO2), thereby obviating the challenges of interpreting equivocal clinical examination or ICP data. Despite these potential advantages, existing NIRS sensors are plagued by technical difficulties that limit clinical utility. Most of these limitations relate to their transcutaneous design that makes them susceptible to both interference from intervening skin/subcutaneous tissue and instability of the skin-sensor interface.
METHODS: We present a flexible, wireless, Bluetooth-enabled, percutaneously introducible intramuscular NIRS device that directly and continuously measures the StO2 of intracompartmental muscle (Figure 1A). Proof of concept for this device is demonstrated in a swine lower extremity balloon compression model of acute CS (Figure 1B), wherein we simultaneously track muscle oxygenation, ICP, and compartment perfusion pressure (PP). The balloon catheter was inserted between the anterior muscle compartment of the hind limb and the anterior face of the tibia to induce CS. The balloon was filled with saline until CS was achieved and maintained for 10 minutes. Experiments were conducted in 4 swine on separate days using different probes to demonstrate reproducibility.
RESULTS: The intramuscular NIRS device generated muscle oxygenation measurements that corresponded with the decreased tissue perfusion associated with acute CS. The observed StO2 decreased with increasing ICP and decreasing PP and then recovered following pressure reduction (Figure 2, representative results). The mean change in StO2 as the PP was decreased from baseline to 30 mmHg was -7.6%. The mean difference between baseline and nadir StO2 was -17.4%. Cross-correlations (absolute value) describing correspondence between StO2 and ICP were > 0.73.
CONCLUSION: This novel intramuscular NIRS device identifies decreased muscle perfusion in the setting of evolving CS. This device addresses the limitations of current cutaneous NIRS devices which are susceptible to interference by skin pigmentation, skin compromise, subcutaneous tissue, and ambient light. In this porcine CS study, the device successfully and continuously monitored muscle StO2, and provided proof of concept for a new diagnostic technology for CS. Future studies will include expanding this device to measure other metabolic products that may be useful in tracking the development of CS.


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