Assessment of Tissue Perfusion in the Lower Limb

Abstract

Downloaded from Bajwa et al Assessment of Lower Limb Perfusion 837when compared with normal limbs and cannot quantify the severity of perfusion deficit. 12 More recent studies show that LDF is a good discriminator of skin flap perfusion and can predict the likelihood of healing after limb amputation.13 LDI is used in preclinical animal models of limb ischemia (eg, the murine hindlimb ischemia model) for high throughput testing of interventions, including angiogenic therapies. The technique allows longitudinal acquisition of data but is limited by motion artifact, ambient temperature variations, and perfusion measurements, which are weighted toward the larger vessels that are shallow and reside on the surface of the limb musculature. 14 Transcutaneous Oxygen PressureThe measurement of transcutaneous oxygen pressure (TcPo 2 ) is a noninvasive technique that allows longitudinal assessment of local oxygen diffusion from the capillary bed through the skin epidermis and provides an indication of the amount of oxygen delivered to the tissue. TcPo 2 measurements can reflect the severity of PAD, 15 assess ulcer healing potential, 16 and determine the optimal level for limb amputation. 17 A TcPo 2 <20 to 30 mm Hg is consistent with CLI, 2,15,18 and levels <40 mm Hg are associated with poor healing after amputation. 18 Inhalation of 100% oxygen would normally result in TcPo 2 >100 mm Hg, but in patients with CLI the TcPo 2 does not rise >30 mm Hg. 18 Oxygen therapy resulting in <10 mm Hg rise in limb TcPo 2 is associated with an >60% chance of an amputation at that level not healing. 18 A rise of >40 mm Hg in TcPo 2 after limb revascularization is considered significant and increases the chances of tissue healing. 15,18 TcPo 2 measurements vary in different tissues and under different physiological conditions. Barriers to diffusion, such as edema, increased oxygen consumption secondary to inflammation, and vasoconstriction, may lead to falsely low TcPo 2 readings falsely. Readings are also affected by temperature, with a 1°C reduction in the thermistor temperature resulting in a 2% to 3% lower TcPo 2 reading. 18 Indocyanine Green Fluorescence AngiographyThis technique has been used for many years to image retinal vessels, 19 and more recently in the assessment of microanastomoses in surgical flap reconstruction surgery, detection of arteriovenous malformations, and measurement of hepatic blood flow. 20 Indocyanine green is a fluorescent dye that is activated by near-infrared laser light at ≈780 nm. 21 This allows a penetrance of 3 mm from the surface of the skin to assess the subdermal microcirculation. 20,22 A semiquantitative measure of perfusion is obtained by measuring pixel fluorescence intensity in different areas of the image from the limb. Perfusion measured by indocyanine green fluorescence angiography correlates with LDI in the hindlimb ischemia model 23 and predicts the likelihood of amputation healing in man. 21 This technique can identify patients with peripheral arterial occlusions who have extensive collater...

Encouraging effects of a short-term, adapted Nordic diet intervention on skin microvascular function and skin oxygen tension in younger and older adults

“…Oxygen Monitoring was used to assess tissue oxygen supply (Bajwa et al 2014). To measure LDF and TcP02 pre and post-intervention, we required participants to attend the laboratory on two occasions, separated by a four-week intervention period, and instructed them to abstain from caffeine prior to attending, to eliminate acute vasoconstriction (Umemura et al 2006).…”

Perfusion Assessment in Critical Limb Ischemia: Principles for Understanding and the Development of Evidence and Evaluation of Devices: A Scientific Statement From the American Heart Association

“…Similar to LSI, ICG fluorescence angiography began as a technique for imaging retinal vessels before use in other applications, including detection of arteriovenous malformation and anastomotic perfusion monitoring after colorectal surgery. 80,81 Fluorescent ICG dye is injected intravenously. The dye is then activated with CLINICAL STATEMENTS AND GUIDELINES near-infrared laser light, producing fluorescence, which can be detected and measured.…”

Nanoparticles for Detection and Treatment of Peripheral Arterial Disease

“…PAD affects around 12 million people in the United States, especially elderly males 65 years and older, and it is linked to high morbidity and mortality rates . Conventional modes of detection (Ankle Brachial Index or ABI, Toe Brachial Index or TBI, and angiography) and treatment (medicine, surgical bypass, endovascular techniques, and cell‐based therapies) of PAD are limited by expensive associated costs, inability for early detection, fibrotic complications, adverse drug side effects, and insignificant changes in ABI reading and/or total oxygen pressure after cell‐based therapies …”

“…Lastly, images produced by angiography have also been reported, but they are limited with the risks of renal toxicity and catheter trauma, and systemic complications from the use of contrast agents . Lastly, elastography and dynamic contrast‐enhanced MRI are deemed very beneficial for detailed information, however, this tool often causes system fibrosis in patients with kidney diseases due to its use of exogenous gadolinium–based contrast agents …”