Microcirculatory Assessment of Arterial Below-Knee Stumps: Near-Infrared Spectroscopy Versus Transcutaneous Oxygen Tension—A Preliminary Study in Prosthesis Users

The Role of Near Infrared Spectroscopy in Diagnosing Stump Ischaemia in Patients with Below Knee Amputation: Case Reports

Introduction

Functional near infrared spectroscopy (fNIRS) can be used to quantify stump oxygen saturation (SaO₂) as one of many possible causes of pain following major amputation. Although commonly used for cerebral perfusion monitoring during carotid or cardiac surgery, it can also be used to monitor tissue perfusion in the lower limb and predict healing following below knee amputation (BKA). The aim of this study was to measure the SaO₂ trend as there is no validated oxygen threshold to diagnose insufficient flow into the arterial collateral network currently.

Report

NIRS was used to measure SaO₂ while performing treadmill exercise. Two BKA patients with chronic stump pain were asked to perform treadmill exercise while using their prosthesis and NIRS optode applied to the posterior stump to monitor SaO₂. Cases 1 and 2 showed a decline in SaO₂ of 25% and 18%, respectively, while walking on the prosthesis. After superficial femoral artery (SFA) recanalisation and stenting, Case 1 showed improvement by maintaining SaO₂ between 54% and 60% throughout treadmill exercise. In Case 2, perfusion could not be further improved, and the patient underwent through knee amputation.

Discussion

fNIRS detected compressive ischaemia and exercise induced ischaemia as mechanisms of stump pain. Findings provided the multidisciplinary team with objective information, aiding decision making to treat stump pain.

A paintable phosphorescent bandage for postoperative tissue oxygen assessment in DIEP flap reconstruction

Flaps are common in plastic surgery to reconstruct large tissue defects in cases such as trauma or cancer. However, most tissue oximeters used for monitoring ischemia in postoperative flaps are bulky, wired devices, which hinder direct flap observation. Here, we present the results of a clinical trial using a previously untried paintable transparent phosphorescent bandage to assess the tissue's partial pressure of oxygen (pO2). Statistical analysis revealed a strong relationship (P < 0.0001) between the rates of change of tissue oxygenation measured by the bandage and blood oxygen saturation (%stO2) readings from a standard-of-care ViOptix near-infrared spectroscopy oximeter. In addition, the oxygen-sensing bandage showed no adverse effects, proved easy handling, and yielded bright images across all skin tones with a digital single-lens reflex (DSLR) camera. This demonstrates the feasibility of using phosphorescent materials to monitor flaps postoperatively and lays the groundwork for future exploration in other tissue oxygen sensing applications.

Comparing near infrared spectroscopy and transcutaneous oxygen measurement in hard-to-heal wounds: a pilot study

Objective:

Oxygen plays an integral role in all phases of the wound healing process and tissue oxygenation is a key determinant of wound healing. A comprehensive evaluation of patients with hard-to-heal wounds must include measurement of oxygenation in and around the area of skin breakdown. The current gold standard, transcutaneous oxygen measurement (TCOM), has numerous drawbacks and as a result has fallen into disuse.

Method:

This study compared measurement of tissue oxygenation of near infrared spectroscopy (NIRS) with TCOM in patients with acute and hard-to-heal wounds. The Shapiro-Wilk test was used to evaluate the normality of the data. The level of agreement between NIRS and TCOM was determined using Bland-Altman analysis. The relationship between TCOM and NIRS was examined using Pearson correlation.

Results:

A total of 24 observations were obtained from 10 patients using TCOM and NIRS. The weighted mean partial pressure of oxygen (pO2) in the study population was 39.54mmHg (8.96 standard deviation). Bland–Altman analysis showed that mean difference was positive (18.75), suggesting an overestimation of oxygen measurements using TCOM compared with NIRS. The oxygen levels measured by TCOM and NIRS showed a strong correlation (r=0.74).

Conclusion:

The wound and hyperbaric community would benefit from a simplified procedure for measuring tissue oxygenation. These findings suggest a strong trend toward correlation between NIRS and TCOM. A further study in a larger population is recommended. NIRS offers several advantages over TCOM. Clinicians have immediate point-of-care visualisation of tissue oxygenation using a handheld device. The procedure takes minutes to perform and is less operator-dependent than TCOM. Finally, NIRS allows measurement of oxygenation in the wound bed, while TCOM does not.

Duplex Ultrasound May Predict the Best Level of Lower Limb Amputation in Patients with Chronic Limb-Threatening Ischemia: A Retrospective Observational Cohort Study

BACKGROUND

Despite improved revascularization options, many patients with chronic limb-threatening ischemia (CLI) require lower limb amputation. Duplex ultrasound (DUS) is recommended as first-choice imaging technique in CLI. However, the prognostic utility of DUS for planning lower limb amputations has never been described before. This study aims to evaluate if DUS and findings from physical examination could be used to help predict the best level of lower limb amputation in patients with CLI.

METHODS

A retrospective cohort of 124 patients with CLI and a lower limb amputation was analyzed. Outcome measurements were reoperation, revision, and conversion rates, which were related to findings from physical examination and DUS examinations.

RESULTS

Thirty-nine reoperations were performed, of which 17 stump revisions and 22 conversions were from below- to above-knee amputation. There was a discrepancy in findings of physical examination and DUS of 25% and 64% of femoral and popliteal pulsations respectively. Conversion rates increased with a more proximal occlusion on DUS. All patients with a vascular occlusion in the aortoiliac trajectory or deep femoral artery required a higher amputation level.

CONCLUSIONS

Physical examination seems to be unreliable, and therefore should not be used to assess the optimal level of lower extremity amputation. Performing a primary above-knee amputation in patients with vascular occlusion in the aortoiliac trajectory or deep femoral artery could significantly reduce reoperation rates.

Peripheral arterial disease screening and diagnostic practice: A scoping review

Early reliable, valid screening, diagnosis, and treatment improve peripheral arterial disease outcomes, yet screening and diagnostic practices vary across settings and specialties. A scoping literature review described reliability and validity of peripheral ischaemia diagnosis or screening tools. Clinical studies in the PUBMED database January 1, 1970, to August 13, 2018, were reviewed summarising ranges of reliability and validity of peripheral ischaemia diagnostic and screening tools for patients with non-neuropathic lower leg ischaemia. Peripheral ischaemia screening and diagnostic practices varied in parameters measured such as timing, frequency, setting, ordering clinicians, degree of invasiveness, costs, definitions, and cut-off points informing clinical and referral decisions. Traditional ankle/brachial systolic blood pressure index <0.9 was a reliable, valid lower leg ischaemia screening test to trigger specialist referral for detailed diagnosis. For patients with advanced peripheral ischaemia or calcified arteries, toe-brachial index, claudication, or invasive angiographic imaging techniques that can have complications were reliable, valid screening, and diagnostic tools to inform management decisions. Ankle/brachial index testing is sufficiently reliable and valid for use during routine examinations to improve timing and consistency of peripheral ischaemia screening, triggering prompt specialist referral for more reliable, accurate Doppler, or other diagnosis to inform treatment decisions.