Measuring Flap Oxygen Using Electron Paramagnetic Resonance Oximetry

Abstract

Objectives/Hypothesis To determine if electron paramagnetic resonance (EPR) oximetry is a viable technology to aid in flap monitoring. Study Design Prospective cohort. Methods This was a cohort study assessing accuracy and speed of EPR oximetry in detecting ischemia of a saphenous artery–based flap in a rat model, using transcutaneous oximetry as a control. Measurements were obtained under both resting and ischemic conditions for nine Sprague Dawley rats (18 flaps), for 3 postoperative days following flap elevation. Results The mean partial pressure of oxygen prior to tourniquet application was 66.9 ± 8.9 mm Hg with EPR oximetry and 64.7 ± 5.2 mm Hg with transcutaneous oximetry (P = .45). Mean partial pressures of oxygen during tourniquet application were 8.9 ± 3.2 mm Hg and 8.5 ± 2.9 mm Hg for EPR oximetry and transcutaneous oximetry, respectively (P = .48), and 67.2 ± 6.9 mm Hg and 65.3 ± 6.1 mm Hg after tourniquet release for EPR oximetry and transcutaneous oximetry, respectively (P = .44). The mean ischemia detection time of EPR oximetry was 49 ± 21 seconds. Conclusions Offering timely, accurate, and noninvasive tissue oxygen measurements, EPR oximetry is a promising adjunct in flap monitoring. Level of Evidence NA Laryngoscope, 129:E415–E419, 2019

OxyChip embedded with radio‐opaque gold nanoparticles for anatomic registration and oximetry in tissues

“…The probe is being evaluated for permanent implantation under an US Food and Drug Administration investigational device exemption and can be removed via surgical resection, for example, during standard‐of‐care en bloc tumor resection 11 . We have shown, in preclinical models and human subjects, that EPR oximetry using the OxyChip is a practical method for measuring tissue pO 2 directly and repeatedly 3,6,12–23 . A phase I clinical study at Dartmouth‐Hitchcock Medical Center (Lebanon, NH) has confirmed that this technique can be applied to human subjects successfully, thus meeting a currently important but unmet need—the ability to make direct, repeated measurements of oxygen in tissue at specific anatomical sites 11,24 .…”

“…11 We have shown, in preclinical models and human subjects, that EPR oximetry using the OxyChip is a practical method for measuring tissue pO 2 directly and repeatedly. 3,6,[12][13][14][15][16][17][18][19][20][21][22][23] A phase I clinical study at Dartmouth-Hitchcock Medical Center (Lebanon, NH) has confirmed that this technique can be applied to human subjects successfully, thus meeting a currently important but unmet need-the ability to make direct, repeated measurements of oxygen in tissue at specific anatomical sites. 11,24 These studies also have provided useful information on some present limitations of EPR oximetry for clinical applications.…”

First-In-Human Study in Cancer Patients Establishing the Feasibility of Oxygen Measurements in Tumors Using Electron Paramagnetic Resonance With the OxyChip

“…This process is sensitive to the partial pressure of oxygen (pO 2 ) at the probe location, with the relaxation rate of the probe increasing as a function of pO 2 in the tissue adjacent to the probe (37,48). The OxyChip is an oxygen-sensing probe containing paramagnetic LiNc-BuO crystals embedded in PDMS for clinical applications (43)(44)(45)(46)(47). The OxyChips used in this study were of a cylindrical shape, 5 mm in length and 0.6 mm in diameter (Figure 1B).…”

“…One such oxygen-sensing paramagnetic material is lithium octa-butoxynaphthalocyanine (LiNc-BuO) crystals (40,42). An implantable oxygen probe, called the OxyChip, has been developed by embedding LiNc-BuO crystals in the oxygenpermeable polymer polydimethylsiloxane (PDMS) for pO 2 measurements (43)(44)(45)(46)(47). Embedding the LiNc-BuO in PDMS shields the crystals from interaction with the biological microenvironment, thereby preventing biochemical degradation and breakdown, as well as local and/or systemic interactions.…”