Continuous monitoring of pO2 and pCO2 by microdialysis indicates physiologic status of the critically ill patients

The monitoring of dissolved oxygen and carbon dioxide in blood or organic tissues is extremely useful for respiratory studies and can be valuable in determining the physiologic status of the critically ill patients. The measurement quantity for both O2 and CO2 sensors is the luminescence lifetime by phase modulation fluorometry. The properties and accuracy of both types of sensors have been firstly characterised in vitro using physiological solutions to demonstrate the fulfilment of the defined requirements for clinical applications. The presented sensors enable the measurement of pO2 in the range 0–300 mmHg and of pCO2 in the range 0–150 mmHg, respectively, with a resolution better than 1 mmHg and accuracy better than 1 mmHg. To verified the operating function of developed sensors in in vivo and to analyse the changes of interstitial pO2 and pCO2 in adipose tissue as indicators of critical ill conditions, several in vivo tests on animal and healthy volunteer have been successfully carried out using a microdialysis catheter CMA 60 for the extraction of interstitial fluid (ISF) from the subcutaneous adipose tissue. Critical conditions similar to intensive care patients have been provoked using two different models: an animal model of haemorrhagic shock and subministration of adrenaline, which causes a local vasoconstriction in the case of experiment with human subjects, respectively. Our results proved that changes in the interstitial pCO2 and pO2 are informative metabolic parameters for critical condition of the patients.