TBI patient monitoring
In collaboration with Kings College Hospital, a microdialysis probe is used to collect dialysate samples from 'at-risk' tissue in traumatic brain injury (TBI) patients. Levels of glucose, lactate and potassium are monitored continuously and in real-time using electrochemical sensors at the patient bed-side. Pyruvate sensors are under development. Potentially debilitating events, known as spreading depolarisations (SDs), are characterised by an increase in potassium, glutamate and lactate levels and a fall in glucose levels. The occurrence of SDs independently predicts poor patient outcome, and is a better indicator than any of the currently used factors. A wireless monitoring system is being deployed that will alert clinicians of the real-time local brain levels of these molecules, indicating SD or ischemic events.
Development of sensors and microfluidic platforms
Miniaturization of the equipment used to monitor chemicals in the intensive care ward is crucial. Flow cells are fabricated using 3D printed techniques to create microfluidic chips for on-chip analysis. Sensors are housed within 3D printed holders for correct placement of sensor within the flow channel. The development of sensors to detect small changes in microdialysate potassium, sodium, glutamate, pyruvate, glucose and lactate levels is on-going. Use of segmented flows (digital microfluidics) can reduce the smearing of chemical changes that is induced by the tubing used to transfer the sample to the analysis equipment. Another option is to use wireless technology to remove the need for the connection tubing altogether. This work is pushing towards wearable technologies.
At the Max-Plank Institute in Cologne, the microfluidic devices and biosensors were fully tested in an animal model before employment onto an intensive care ward. Tissue sensors, on-line microfluidic sensors, rsMD and laser speckle techniques were used in these animal studies to monitor the tissue during needle-prick induced SD events. Results validate the use of microfluidic sensors and show in depth anlaysis of the tissue response.
Continuous measurements of brain glucose and lactate in a porcine model have been conducted in Rigshospitalet in Copenhagen. The wireless system was deployed and used successfully to monitor the ischemic insults on the brain during cardiac arrest and resuscitation.
Tissue monitoring during free-flap reconstructive surgery
Glucose and lactate levels were monitored during free-flap surgery at Queen Alexandra Hospital in Portsmouth. Here a microdialysis probe was implanted in the donor tissue. Glucose and lacate were monitored using rsMD throughout the surgery. When the tissue was disconnected from the body's blood supply and was transferred to the recipient site, the level of glucose fell and lactate increased, indicating that the tissue was at ischaemic risk. When reconnection of the blood supply occurred during the reconstruction phase, successful reperfusion to the microvasculature was indicated by a reversal of the trends. The ratio of lactate to glucose is a clear indicator of the onset of ischeamia and the subsequent tissue recovery. The flap was also monitored overnight in the intensive care ward.
Another cohort of patients will be monitored using the updated microfluidic technology in the near future.
Assessing transplant kidney health
Porcine kidneys were collected by trained personnel who mimicked the conditions of human kidney retrieval. The kidneys were assessed for levels of creatinine within the vein, urine and artery. Both injured and uninjured kidneys were assessed and the ability of the kidney to clear an injected bolus of creatinine was assessed. The aim of this work was to create an online monitoring system to assess marginal kidneys for transplantation.
Acute compartment syndrome
A wireless system for measuring glucose, lactate and potassium has been devised to assess the potential risk of a patient developing ACS. Work is on-going to monitor patients in a pilot study.