The use of online rapid sampling microdialysis in the clinical detection of tissue ischaemia

Tissue ischaemia has a varied aetiology and presentation, with the potential to affect multiple organ systems and lead to significant morbidity and mortality. The detection of clinical ischaemia with microdialysis sampling forms the primary focus of this work. Microdialysis (MD) allows the extracellular composition of tissue to be characterised in vivo and is incorporated into a new class of analyser. Rapid sampling on-line microdialysis (rsMD), analyses the dialysis liquid stream from a patient on-line, at high time resolution. The device has been validated in ex-vivo bench work and animal studies, however I aimed to utilise this technology to create a tool that reliably detects tissue ischaemia in the following clinical settings: 1. Detection of colonic ischaemia following abdominal aortic aneurysm (AAA) repair 2. Detection of an anastomotic leak following formation of a gastrointestinal (GI) anastomosis 3. Renal transplant allograft viability assessment in the preservation period In a prospective observational study of 10 patients undergoing AAA repair, a MD catheter was tunnelled into the mesentery of the sigmoid colon. Each patient underwent monitoring for incremental changes in the concentration of the metabolic markers of ischaemia. I identified transient subclinical ischaemic events that have not been previously described and demonstrated that MD may act as an effective tool in the early diagnosis of colonic ischaemia. In my second study, I aimed to assess the feasibility of using rsMD in the early detection of anastomotic leaks following formation of a GI anastomosis. I developed an ex-vivo MD protocol for intraperitoneal lactate measurement and sampled drain fluid from 20 patients having undergone GI surgery. In a confirmed anastomotic leak, I identified a rise in intraperitoneal lactate concentrations 3 days prior to the development of symptoms and 7 days prior to the confirmation of the diagnosis. In my final study, I aimed to assess the feasibility of utilising rsMD for organ viability assessment in a DCD porcine model. 7 un-perfused and 8 perfused kidneys were monitored at room temperature in the control group with 5 kidneys monitored in the preservation group. These kidneys underwent SCS after retrieval, followed by tissue monitoring. This preliminary study provided a baseline ischaemic profile for porcine kidneys whilst validating the technique, allowing appropriate comparison when examining the effect of organ preservation via SCS or HMP. 14 porcine kidneys were subjected to 15 minutes warm ischaemia, then placed upon models of SCS or HMP. I demonstrated that HMP appears superior to SCS at attenuating injury accumulated during warm ischaemia and that rsMD is feasible for the assessment of lactate concentration during organ preservation.Open Acces