The SensiCathTM arterial blood gas (ABG) monitoring system allows rapid blood gas and pH measurements using fiber optic sensors in a paracorporeal device. The paracorporeal device location allows blood to be withdrawn from a vascular access, measured and returned to a patient, without direct handling and blood loss associated with traditional sampling techniques. The disposable device contains three fiber optic sensors and one temperature sensor. The sensors are monitored using a three-channel, solid-state instrument of minimal size and weight. Measurements of pH, pCO2, and pO2 are made at the point of care, on demand, with results available in 60 seconds. Calibration is performed using two prepackaged, sterile, nontoxic, nonpyrogenic solutions. The paracorporeal location allows access for calibration before or during patient utilization, and for quality assurance checks at any time during use. Laboratory data are presented which assess precision and accuracy of the SensiCath system by comparing its performance measured against tonometered gases and a calibrated pH glass electrode. In vivo animal data using a rabbit model indicate the SensiCath system performance is compared against two independent standard blood gas analyzers. The clinical utility of the SensiCath system incorporated into standard arterial lines is discussed.