Interstitial pH, pO2 and pCO2 controlled by optical sensors

The continuous monitoring of interstitial pH, pO2 and pCO2 contained in the adipose tissue of intensive care patients, is one of the objective of the four year European project CLINICIP (Closed Loop Insulin Infusion in Critically Ill Patients). A glass capillary on line with the microfluidic system, is the solid support onto which the appropriate chemistry is immobilised. The optical working principle applied for the detection of oxygen and carbon dioxide is the modulation of the fluorescence lifetime, whereas absorption modulation is the approach followed for the pH detection. On this basis, two different optoelectronic units were developed for the interrogation of the glass capillary, one for life-time measurements and the other for absorption measurements. Preliminary tests demonstrated a resolution of 0.03 pH units for pH; < 0.55 mmHg for oxygen and < 0.6 mmHg for carbon dioxide; and an accuracy of 0.07 pH units for pH; < 1 mmHg for oxygen and < 1.5 mmHg for carbon dioxide.