Smartphone-Mounted Infrared Thermography Camera to Assess Success of Open Infrainguinal Revascularisation

Abstract

Introduction - Early thrombosis occurs in around 7% of infrainguinal vein bypass grafts(1). Recognition of this complication and prompt reintervention may salvage the graft and the limb. Peri-operative monitoring of graft patency is often dependent on nursing and other non specialist staff. In the presence of calf artery disease and poor runoff peripheral pulses are often impalpable and assessment of graft patency may be difficult. Frequently graft thrombosis may remain unrecognised. The aim of this study was to assess the role of a smartphone-mounted infrared thermography (IRT) camera to monitor bypass graft patency in the early postoperative period. Methods - 10 consecutive patients undergoing infrainguinal vein bypass surgery for critical ischaemia at a tertiary referral vascular unit were recruited. Thermography images of the soles of both feet were taken using a smartphone-mounted IR camera on the morning before surgery and the morning after surgery. The images taken were immediately available on the smartphone and mean temperature of four different areas of the sole based on angiosome distribution (medial heel, lateral heel, medial forefoot, lateral forefoot) and the pulps of the hallux and the third toe (when present or adjacent toe when amputated) were measured using the smartphone application. The relative change in temperature differences between the two feet between the pre and postoperative images in the six areas was then calculated. All grafts underwent duplex scanning to assess for patency in the postoperative period. Results - n 9 out of 10 cases there was a significant increase in relative temperature difference between the two feet between the pre and post operative images in all areas with the revascularised foot being warmer (mean relative change in temperature +4.47 degrees celsius). The biggest positive shifts in relative temperature occurred in the lateral forefoot and the big toe (5.6; STD 3.02; 6.23 STD 3.46). In one case the temperature difference between the two feet showed a negative shift with the treated foot being cooler (mean relative change in temperature -6.66 degrees celsius). On duplex scanning the 9 cases with a positive shift in relative temperature difference had a patent graft while the case with a negative shift had an occluded graft. This was successfully thrombectomised and the distal anastomoses revised. Visualisation of the colour palette representation of the temperature pattern of the foot alone was sufficient to identify a positive shift in the 9 cases with a patent graft as well as a negative shift in the one occluded graft. (See image) Conclusion - A smartphone mounted infrared thermography camera provides a quick, simple and relatively cheap technique for effective monitoring of infrainguinal bypass graft patency in the early postoperative period. The colour pattern representation of the temperature pattern of the foot allows non specialist staff to easily identify significant negative shifts in temperature triggering specialist assessment of graft patency.