The Near Infra-red Spectroscopy Plantar-Palmer Index is a Viable Alternative to the Ankle-Brachial Index for Peripheral Arterial Disease Screening

Introduction:  The Ankle Brachial Index (ABI) is a widely used diagnostic technique for peripheral artery disease (PAD), which involves measuring the ratio of blood pressure in the ankle to the blood pressure in the arm. The ABI procedure can be time-consuming, labor intensive, technically challenging, and uncomfortable for patients.  As a screening technique the ABI has been shown to have poor sensitivity and unreliable in diabetic patients.  These limitations have spurred the development of novel imaging techniques for PAD screening.Methods:  Near infrared spectroscopy (NIRS) (SnapshotNIR, Kent Imaging LLC, Calgary, Canada) is an imaging device that can measure the levels of oxygenated and de-oxygenated hemoglobin in tissues to calculate and create an image of tissue oxygen saturation. NIRS is non-invasive and has demonstrated efficacy to assess tissue perfusion quickly at the bedside in patients with PAD.  The Planter-Palmer Index (PPI) is performed with a series of 3 NIRS images – the palm or upper arm as a reference and two images of the plantar surface of the foot. The first image of the planter foot is taken with the patent lying supine. The 2nd image of the planter foot is captured after elevating the limb to 45 degrees for 1 minute. Once the images are collected, a similar calculation to the ABI occurs using STO2 data points of the metatarsals and metacarpals. The STO2 Delta between the supine and elevated planar images is also calculated.Results:  A series of 75 patients were studied.  The cohort include both healthy subjects as well as patients with various degrees of PAD. Both ABI and PPI assessment was accomplished.  The PPI compared favorably to the ABI but was shown to be more efficient from a procedural time requirement standpoint.  Patients tolerated both procedures well.   It was noted that in patients with elevated ABIs due to noncompressible vessels, the STO2 Delta was useful to help determine severity of PAD, as larger Deltas correlated with more severe disease.Discussion:  While the ABI remains deeply entrenched in clinical assessment of PAD, the NIRS-PPI is provocative as an alternative.  The NIRS-PPI could replace the ABI as the method for assessing both the presence and severity of PAD in patients by providing more comprehensive and accurate evaluation. Further research and clinical trials will be essential to validate these methods and establish standardized protocols for their implementation in routine clinical practice.References:Tehan PE, Santos D, Chuter VH. A systematic review of the sensitivity and specificity of the toe–brachial index for detecting peripheral artery disease. Vascular Medicine. 2016;21(4):382-389. doi:10.1177/1358863X16645854 Crowell A, Meyr AJ. Accuracy of the Ankle-brachial Index in the Assessment of Arterial Perfusion of Heel Pressure Injuries. Wounds. 2017 Feb;29(2):51-55. PMID: 28272012. Wang Z, Hasan R, Firwana B, Elraiyah T, Tsapas A, Prokop L, Mills JL Sr, Murad MH. A systematic review and meta-analysis of tests to predict wound healing in diabetic foot. J Vasc Surg. 2016 Feb;63(2 Suppl):29S-36S.e1-2. doi: 10.1016/j.jvs.2015.10.004. PMID: 26804365. Chuter V, Schaper N, Hinchliffe R, Mills J, Azuma N, Behrendt CA, Boyko EJ, Conte MS, Humphries M, Kirksey L, McGinigle KC, Nikol S, Nordanstig J, Rowe V, David R, van den Berg JC, Venermo M, Fitridge R. Performance of non-invasive bedside vascular testing in the prediction of wound healing or amputation among people with foot ulcers in diabetes: A systematic review. Diabetes Metab Res Rev. 2024 Mar;40(3):e3701. doi: 10.1002/dmrr.3701. Epub 2023 Jul 26. PMID: 37493206. Chuter V, Schaper N, Mills J, Hinchliffe R, Russell D, Azuma N, Behrendt CA, Boyko EJ, Conte MS, Humphries M, Kirksey L, McGinigle KC, Nikol S, Nordanstig J, Rowe V, van den Berg JC, Venermo M, Fitridge R. Effectiveness of bedside investigations to diagnose peripheral artery disease among people with diabetes mellitus: A systematic review. Diabetes Metab Res Rev. 2024 Mar;40(3):e3683. doi: 10.1002/dmrr.3683. Epub 2023 Jul 21. PMID: 37477087.