Detection of Flap Ischemia Using Interstitial Glucose Monitor

Background: Breast reconstruction involving microvascular free tissue transfer is a major, labour-intensive operation that provides numerous benefits for patients' psychosocial function and well-being. Flap failure, though rare, is a devastating complication and leads to serious morbidities. It can occur in the first 24-72 hours after the operation. However, if ischemia is detected earlier, the chances for operative salvage are better. Unfortunately, the current monitoring process remains mostly subjective. A simple device that objectively assesses flap perfusion - either as a stand-alone tool or an adjunct to the current monitoring method - would be a tremendous improvement in detection of early postoperative flap ischemia and, in turn, increase flap salvage and survival. Purpose: The overall objective of this clinical pilot study is to examine the accuracy and reliability of measuring interstitial glucose levels using Continuous Glucose Monitoring (CGM) technology as an objective method of detecting postoperative flap tissue ischemia in patients undergoing free flap-based reconstructive surgery. Methods: In this pilot cohort study, the investigators aim to prospectively include 30 free flaps in total from 10-20 patients undergoing DIEP-based breast reconstruction by one surgeon at Juravinski Hospital. Patients will be recruited at the pre-operative consultation. The transcutaneous sensor of the CGM device will be inserted into the subcutaneous layer of the flap upon completion of surgery, while an additional sensor will be placed on the patient's thigh as control. These devices are blinded and will start recording the flap's interstitial glucose levels. The patient will be admitted and the flap will be assessed clinically as per protocol. On-call residents will be given a data collection sheet to document the exact time they were alerted about a flap, the clinical finding, and the subsequent decision made. Once an endpoint has been reached for a flap, the CGM sensor will be removed and its data extracted. Data Analysis: The timing of occurrence of low interstitial glucose levels and rapid glucose level decline will be analyzed with the timing of clinical concerns raised about the flap. The systemic glucose level will be used as a control for the flap glucose level. The investigators aim to analyze the temporal correlation between interstitial glucose measurements and clinical findings of the flap's vascular status (eg. vessel occlusion, ischemia). Statistical analysis will be done with assistance by a biostatistician.