Is There Adequate Perfusion for Healing? What Routine Noninvasive Vascular Studies are Missing?

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Adequate vascular supply, eradication of infection, and transition out of the inflammatory phase of wound healing are key to expediting limb salvage in the face of lower extremity ulceration.¹ Proper vascular assessment begins with pulse palpation and Doppler evaluation of the foot; absent or weak palpable pulses in conjunction with weak or non-Dopplerable signal prompts providers to obtain routine noninvasive vascular studies to determine if formal vascular evaluation is required. Current routine noninvasive vascular studies include ankle and toe pressure measurements (AP and TP, respectively), ankle-brachial index (ABI) and toe-brachial index (TBI) measurements, pulse waveform recordings, transcutaneous oxygen pressure measurements (TCOM), skin perfusion pressure, and duplex scanning.² However, results of these studies are often unreliable in patients with lower extremity ulcerations due to medial calcinosis, scarring, wounds, prior amputations, infection, and/or edema.^2-6 Certain methods also are technically challenging, costly, and time consuming, and none provide site-specific information on adequate perfusion or oxygenation for healing.^7,8  Providers must often rely on clinical judgement, which may prolong wound healing times and increase the risk for further complications.⁸

Near-infrared imaging (NIRI) assessment has been utilized for decades to assess tissue oxygen saturation levels in the diagnosis of peripheral arterial disease (PAD), breast cancer, gastrointestinal pathology, optical detection of cancer, and diabetic foot ulceration assessment.^9-24 One modality of NIRI assessment provides rapid, real-time objective assessment of site-specific tissue oxygen saturation due to differing optical signals received based on the oxygen carrying status of hemoglobin simply by taking a photograph of the area of concern.

Presented herein is a case highlighting the ability of the aforementioned device to detect factors that would contribute to delayed wound healing in a patient in which routine noninvasive vascular studies were unreliable.

An 80-year-old Caucasian man, with a history of diabetes mellitus, PAD with previous intervention, and right below-knee amputation, presented with chronic ulceration of the left lateral malleolus (Figure 1A) and fifth metatarsal base with concurrent metatarsal osteomyelitis. Noninvasive vascular studies were consistent with adequate perfusion for healing at initial assessment (AP, 110 mm Hg; ABI, 0.75 mm Hg; TP, 45 mm Hg; TBI, 0.31 mm Hg). Use of a handheld NIRI device (KD203; Kent Imaging Inc, Calgary, Alberta, Canada) revealed increased tissue oxygen saturation in the immediate periwound tissues about the lateral malleolar ulceration and fifth metatarsal area. The area was about 1 cm to 2 cm from the periphery of the wound edge and had reduced tissue oxygenation signal of mottled appearance (Figure 1B). The patient progressed with advanced local wound care consisting of serial debridement, offloading, toptical antibiotics, and foam dressings given the results of the noninvasive vascular studies.

Two months later, deterioration of the lateral malleolar wound led to obtaining repeat noninvasive vascular studies. Results at that time were consistent with improved perfusion (AP, 118 mm Hg; ABI, 0.89 mm Hg; TP, 80.2 mm Hg; TBI, 0.61 mm Hg), prompting rearfoot TCOM to be obtained. The result from the TCOM probe placed anteriorly to the wound was 52 mm Hg, while the probe placed proximally to the wound was 17 mm Hg (Figure 1B). Discrepancies and inconsistencies in these results prompted formal vascular evaluation. A computed tomography angiogram revealed a popliteal aneurysm and 2-vessel runoff to the left foot with high-grade stenosis of the proximal posterior tibial artery. The patient subsequently underwent femoral to popliteal artery bypass with reverse saphenous vein graft with repair of the popliteal aneurysm. A more distal bypass was not possible for this patient. Repeat assessment with the handheld device revealed a reversal in the signal pattern with reduced periwound signal and increased signal within the wound base of the lateral malleolar ulceration (Figure 2).

Routine noninvasive vascular studies only provide information on pressure to the ankle and toes and single-point assessment of peripheral wound tissue perfusion. Treating providers must extrapolate if adequate perfusion to the wound exists for healing, utilizing the results of these routine noninvasive studies and clinical judgement.⁸ Results of these studies also can be adversely affected by a variety of factors, particularly in patients with diabetes, end-stage renal disease, and critical limb ischemia, as well as being time consuming and counterproductive to clinic flow.^2-7 Use of a handheld, noncontact, noninvasive NIRI device in this case was able to provide objective information on site-specific tissue oxygenation by simply taking a photograph of the wound. Baseline images were consistent with local ischemia, chronic inflammation, and infection while repeat assessment following vascular intervention revealed transition to the proliferative phase of wound healing.

Near-infrared imaging of chronic wounds in patients with diabetes has been shown to be able to assess changes in microcirculation and predict healing outcomes better than serial wound assessment.^19-21 Its use may enable physicians to begin earlier aggressive treatment for expeditious wound resolution. The main limitation of its use is learning how to correctly interpret the NIRI images obtained. Tissue oxygen saturation levels can be affected by the capacity for pulmonic gas exchange; hemoglobin levels; the peripheral perfusion rate, which can vary with the severity of PAD present; chronic inflammation; and infection.^25-27

Although increased signal with this modality in the surgical setting signifies adequate tissue perfusion and oxygenation, the images obtained when imaging chronic wounds is quite different. One must first understand the current state of the wound. Wound beds can be hypoxic even when global tissue oxygen saturation levels are normal due to local pathologic changes in the vascular bed, periwound fibrosis, and edema, which increases the distance between capillaries. The inflammatory phase of wound healing, in which chronic ulcers are stalled, appears as increased periwound signal and reduced signal at the wound base, signifying a hypoxic wound bed.²⁵ In this phase of healing, peripheral collaterals will dilate in attempts to supply the wound with required nutrients for healing, yet the base of the wound is lacking, particularly in oxygen. This may explain the discrepancy seen in the TCOM readings obtained 2 months later, as the anterior probe was placed in the location of dilated collaterals while the proximal probe provided a more realistic reading in regards to the local ischemia present about the wound.

Peripheral arterial disease with this type of imaging most often has a mottled pattern of signal appearance,^25,28 as shown in Figure 1B. Transition to the proliferative phase of healing results in reduced periwound signal and increased signal within the wound bed. This signifies increased oxygen within the wound bed, a crucial component of angiogenesis and granulation tissue formation, the tenants of the proliferative phase of healing.^8,29,30 This transition was evident in the case presented here with the image assessment obtained following vascular intervention (Figure 2B). Infection related to osteomyelitis of the fifth metatarsal was seen as an increased signal on baseline assessment in the present case (Figure 2B), consistent with previous reports.^25,28 Reduced tissue oxygenation signal levels within the fifth metatarsal following vascular intervention most likely occurred due to increased distal blood flow enhancing antibiotic therapy delivery to this area.

Understanding characteristic patterns of local ischemia, ulcers stalled in the chronic inflammatory phase, transition to the proliferative phase of healing, and infection seen with NIRI in chronic wounds is crucial. Without knowledge of these signal patterns, the baseline images obtained in this case may have been misinterpreted as signifying adequate perfusion and oxygenation and worsening of the condition following vascular intervention.

Rapid assessment with a handheld NIRI device was able to detect tissue oxygenation deficiency to the lateral malleolar wound bed when routine noninvasive vascular study results indicating adequate perfusion for healing were inconsistent. The NIRI with this device is simple and quick to obtain. Tissue oxygen saturation levels can be determined anywhere on the image, obtained either at the time the image is captured or when reviewing the image at a later date, which is particularly helpful when performing serial assessment of the wound. The addition of this assessment modality may enhance clinical decision making, help expedite vascular evaluation and intervention, and reduce healing times, complications, and associated wound care costs.

Affiliation: Mercy Hospital, Cedar Rapids, IA

Correspondence: Jonathan F. Arnold, MD, ABPM-UHM, CWS-P, Medical Director, Mercy Healing Center, Mercy Hospital, 701 10th Street SE, Ground Floor, Cedar Rapids, IA; jlarnold@mchsi.com

Disclosure: Dr. Arnold received the study device from the manufacturer for research purposes. Manuscript preparation was provided by www.scriptummedica.com. Results of this paper were presented as a poster at the Spring Symposium on Advanced Wound Care (SAWC), Charlotte, NC, April 25–29, 2018.