Using Near Infrared Spectroscopy Imaging to Manage Critical Limb Ischemia

Near infrared spectroscopy (NIRS) has the potential to monitor tissue oxygenation to manage critical limb ischemia (CLI). These authors demonstrate the technique in a 54-year-old woman who experienced significant incisional and digit tissue ischemia following treatment for left foot deformities and bunions.

Critical limb ischemia (CLI) is considered a clinical syndrome characterized by prolonged (≥2 weeks) ischemic rest pain, and nonhealing wounds/ulcers/gangrene in one or both legs due to clinically established arterial occlusive disease.¹ The clinical characteristics of CLI are determined by the degree of ischemia and coexisting infections, and are associated with higher risks of limb loss, quality of life impairment, cardiovascular events, and death, with a mortality rate of 20% within 6 months after the diagnosis.² The poor prognosis demands a multidisciplinary, coordinated approach involving specialists from various clinical disciplines for rapid assessment, revascularization, and wound care management to enhance patient outcomes.

The preliminary clinical assessment to diagnose CLI includes physical examination and ankle-brachial index (ABI) evaluation, which can measure macroscopic blood flow to the limb. Unfortunately, ABI fails to detect early phases of atherosclerotic progression and is unreliable in patients with vascular calcification and provides little information regarding perfusion of the skin. Another measure, the toe-brachial index (TBI) evaluation, remains ambiguous for the diagnosis of CLI.³ Other techniques, such as duplex ultrasound, computerized tomography or magnetic resonance angiography, and formal invasive angiography, are useful to diagnose the anatomic location and severity of disease as well as to identify lesions that can be treated by revascularization. Continuous monitoring of the hemodynamic characteristics (perfusion of oxygenated blood) after revascularization is clinically relevant in monitoring and managing patients with CLI. Noninvasive transcutaneous oxygen (TcO₂) perfusion offers clinicians an opportunity to monitor tissue oxygenation at a specific location, but the lack of reproducibility due to patient and tissue characteristics makes routine utilization of TcO₂ challenging.

Once the perfusion is reestablished, wound management in CLI may require various therapies including debridement, infection management, appropriate topicals, offloading, negative pressure therapy, and hyperbaric oxygen therapy (HBOT) to promote wound healing. Many of the above-mentioned diagnostic methods are technically challenging, costly, and time consuming and provide no specific information on perfusion or oxygenation of tissues. More recently, a noncontact, noninvasive technique based on near infrared spectroscopy (NIRS; Snapshot_NIR; Kent Imaging, Calgary, AB, Canada) using multiple wavelengths, capable of determining oxygen saturation (StO₂), relative oxyhemoglobin level (HbO₂), and relative deoxyhemoglobin (Hb) level in superficial tissues, is extensively used to continuously monitor and measure perfusion of tissues.

The authors of this article present a case study and demonstrate the clinical utility of noncontact, noninvasive NIRS imaging in the management of CLI.

Case Report

A 54-year-old woman, a nondiabetic and nonsmoker with no history of taking medication, had podiatric surgical intervention for left foot deformities and bunions. The postoperative visit a week later demonstrated significant incisional and digit tissue ischemia. Two days later a second postoperative visit demonstrated continued advancement of tissue ischemia and the patient was referred to a wound care specialist for evaluation and consideration of hyperbaric oxygen therapy.

The initial wound clinic findings revealed necrosis of the distal aspect of digit D3, incisional necrosis, and diffuse tissue ischemia with cyanosis and mottling of the dorsum of the foot (Figure 1a). NIRS imaging (Snapshot_NIR) revealed poorly perfused tissues in the distal aspect of digit D3 along incisions and diffusely across the foot (Figure 1b).

The left foot was cold with diminished pulses. No Doppler signal was observed in the dorsalis pedis (DP) artery. There was a weak Doppler signal in the posterior tibial (PT) artery. The presentation met the criteria for CLI. The patient's surgical history was significant for 2-hour tourniquet time. The patient was seen in urgent vascular consultation and underwent angiography and endovascular arterial intervention the next morning. The angiographic findings demonstrated acute arterial embolization with significant compromise of the anterior tibial artery, PT artery, and digital arch (Figure 2a). Angioplasty was performed on the anterior tibial artery, PT artery, and digital arch (Figure 2b) followed by administration of intra-arterial nitroglycerin. Recanalization of the DP arch was accomplished (Figure 2c).

The angiographic evaluation confirmed the clinical suspicion that distal embolization was caused by intraoperative tourniquet injury and intra-arterial clotting that showered distally after deflation of the tourniquet. Post-angiogram (Figure 3c and Figure 3d) and endovascular intervention shows improvement of tissue ischemia from pre-angiogram (Figure 3a and Figure 3b). NIRS imaging pre-op and post-op confirmed the clinical findings and demonstrated significant improvement in tissue oxygenation. Immediately following angiogram and endovascular intervention, HBOT was administered (2.0 ATA x 90 min) and NIRS imaging was performed, which demonstrated intense improvement of tissue hemoglobin oxygenation saturation (Figure 4).  

Conflicting evidence exists on the beneficial effects of HBOT in treating CLI. However, studies have shown that HBOT increases the amount of dissolved oxygen in arterial blood, leading to hyperoxia even in poorly perfused tissues, augmented circulating levels of endothelial progenitor cells (EPCs) and soluble angiogenesis factors.⁴ HBOT is considered as a good adjunct therapy that can increase hemodynamic parameters in CLI.⁵

HBOT was continued and the patient continued to demonstrate improved clinical appearance, with no return of tissue ischemia. Progress was longitudinally monitored via NIRS imaging, which correlated well with clinical findings. Wound care initially consisted of betadine to necrotic tissues and the patient maintained strict non-weightbearing. Based on improvement in the clinical appearance and enhanced NIRS values, HBOT was suspended after a total of 22 sessions. The stabilization of hemodynamic parameters was monitored using NIRS imaging. Topical therapy was changed to REDOX Gel (RxOS Medical Inc, Morton Grove, IL) mixed with Iodoflex (Smith & Nephew, Andover, MA). Comparison of 7-week (Figure 5a) and 18-week follow-up (Figure 5b) demonstrated significant clinical improvement and D3 was completely healed at 18 weeks with salvage of the entire digit. Radiographic imaging revealed an excellent surgical outcome.

In Conclusion

NIRS is a noncontact, noninvasive, rapidly emerging imaging technology that can measure tissue oxygenation that correlates with perfusion. NIRS provides rapid results and eliminates many of the limitations associated with other labor-intensive and invasive imaging modalities such as hazardous intravenous dyes. The authors of this article utilize handheld Snapshot_NIR for longitudinal monitoring of tissue perfusion to predict healing outcomes in patients with CLI and have found that NIRS is highly cost effective, time efficient, and safe. The faster sampling time and ability of Snapshot_NIR to save data in various formats allow clinicians to integrate the data with existing electronic health records. The hemodynamic changes measured using Snapshot_NIR after endovascular revascularization and HBOT allow clinicians to use this technology to determine treatment protocols and understand healing characteristics in CLI.

Sandeep Gopalakrishnan, MS, PhD, DAPWCA, is an Assistant Professor in the College of Nursing, University of Wisconsin Milwaukee.

Jonathan A. Niezgoda, MA, is a Hyperbaric Technician at Advancing the Zenith of Healthcare (AZH) Wound and Vascular Center, Milwaukee, WI.

Brandon C. Hoffman, BS, is a Medical Assistant at Advancing the Zenith of Healthcare (AZH) Wound and Vascular Center, Milwaukee, WI.

Awais Siddique, MD, is an Endovascular Radiology Medical Director at Advancing the Zenith of Healthcare (AZH) Wound and Vascular Center, Milwaukee, WI.

Jeffrey A. Niezgoda, MD, FACHM, MAPWCA, CHWS, is the President, Chief Executive Officer and Corporate Medical Director of Advancing the Zenith of Healthcare (AZH) Wound and Vascular Center in Milwaukee, WI.

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