Intravascular carbon dioxide monitoring using micro-flow colorimetry

Continuous oxygen monitoring in subcutaneous adipose tissue using microdialysis

A measurement system, consisting of an optochemical glass capillary oxygen sensor, an optoelectronic measuring unit and a microdialysis catheter (CMA 60) for the extraction of the biological fluid from the subcutaneous adipose tissue of critically ill patients is reported. The capillary sensor is based on the oxygen sensitive dye platinum (II) meso-tetra(pentafluorophenyl) porphyrin (Pt-TFPP) incorporated in a polystyrene matrix. The measuring system has been tested in vitro and in vivo. In particular in vitro long-term stability of the sensor has been investigated in different measurement media (elomel, 5% mannitol, Ringer, dialysed blood). The influence of different flow rates from 0.1 up to 7.0 microl min(-1) on the sensor response as well as the oxygen recovery rate are discussed. The presented measurement system allows the measurement of oxygen in biological fluid in the range from 0 to 300 mmHg, with a resolution better than 1 mmHg and high accuracy (better than +/-1 mmHg absolute). Finally, the suitability of the described measurement system for the continuous oxygen monitoring in subcutaneous adipose tissue has been proved in in vivo investigations performed on test animals.

Evaluation of microfluidic blood gas sensors that combine microdialysis and optical monitoring

It is shown that microdialysis-based blood gas (pH, pCO2 and pO2) optical sensors are stable for durations of several hours in blood. This performance is uncommon with many types of membrane sensor. Microdialysis techniques can be designed to ensure that the sweep microflow samples are in biochemical equilibrium with the bulk media, even after hours of exposure to the complex composition of blood. The rate of diffusion through the membrane is not the determining factor in sensor reading, as it is with other sensor techniques that consume the analyte. The sweep fluid 95% equilibration times for microdialysis fibres were approximately double in blood compared with buffer, reflecting slower diffusion of ions. This is in contrast to the equilibration of gases through silicone hollow-fibre membranes in blood, which showed unchanged equilibration times between blood and buffer. Sensor measurements correlate well with a blood gas analyser for up to 9 h in blood, with correlation coefficients of 0.973 for the pO2 sensor 0.974 for the pCO2 sensor and 0.947 for the pH sensor. In blood, the sensors have precisions of 1.7 mmHg, 3.7 mmHg and 0.019 pH units and bias levels of -0.7 mmHg, 1.2 mmHg and 0.002 pH units, for pO2, pCO2 and pH, respectively.

Implantable chemical sensors for real-time clinical monitoring: progress and challenges

Recently, progress has been made in the development of implantable chemical sensors capable of real-time monitoring of clinically important species such as PO(2), PCO(2), pH, glucose and lactate. The need for developing truly biocompatible materials for sensor fabrication remains the most significant challenge for achieving robust and reliable sensors capable of monitoring the real-time physiological status of patients.