We describe a bedside arterial blood gas (ABG) monitoring system which uses fluorescent optical sensors in the measurement of blood pH, PCO2 and PO2. The Point-of-Care Arterial Blood Gas Monitoring System consists of the SensiCathTM optical sensor unit manufactured by Optical Sensors Incorporated and the TramTM Critical Care Monitoring System with ABG Module manufactured by Marquette Electronics Incorporated. Current blood gas measurement techniques require a blood sample to be removed from the patient and transported to an electrochemical analyzer for analysis. The ABG system does not require removal of blood from the patient or transport of the sample. The sensor is added to the patient's existing arterial line. ABG measurements are made by drawing a small blood sample from the arterial line in sufficient quantity to ensure an undiluted sample at the sensor. Measurements of pH, PCO2 and PO2 are made within 60 seconds. The blood is then returned to the patient, the line flushed and results appear on the bedside monitor. The ABG system offers several advantages over traditional electrochemical analyzers. Since the arterial line remains closed during the blood sampling procedure the patient's risk of infection is reduced and the caregiver's exposure to blood is eliminated. The single-use, disposable sensor can be measure 100 blood samples over 72 hours after a single two-point calibration. Quality Assurance checks are also available and provide the caregiver the ability to assess system performance even after the sensor is patient attached. The ABG module integrates with an existing bedside monitoring system. This allows ABG results to appear on the same display as ECG, respiration, blood pressure, cardiac output, SpO2, and other clinical information. The small module takes up little space in the crowded intensive care unit. Performance studies compare the ABG system with an electrochemical blood gas analyzer. Study results demonstrated accurate and precise blood gas measurement of 100 samples and 72 hour performance without need for re-calibration.