ONLINE ARTERIAL BLOOD-GAS ANALYSIS WITH OPTODES - CURRENT STATUS

Objectives: To summarize the rationale for and the principles of blood gas and pH measurement with photochemical sensors (optodes) placed in the arterial line-either intravascularly (in vivo) or extravascularly (ex vivo). To review the specific problems that occur with in vive me asurement; the clinical data that have been obtained with continuous i ntravascular and on-demand extravascular systems; and, the role of thi s technology in the intensive care unit. Methods and results: The prin ciples of absorbance and fluorescent optical sensors are described. Th e accuracy of intravascular PO2 optodes can be affected by thrombosis, the wall effect (if the sensor touches the arterial wall it may read tissue values) and reduced blood flow past the sensor. Current optical pH, PCO2 and PO2 probe/cannula designs, including hybrid probes with electrochemical PO2 sensors, have not yet fully overcome these problem s of the intravascular milieu. On-demand blood gas monitors that locat e the optodes extravascularly, within the radial artery line, avoid th ese intravascular measurement problems. On-demand systems can have acc uracy comparable to conventional laboratory blood gas analyzers. With either intravascular or extravascular measurement large patient studie s are lacking and the relevant cost benefit ratios are not known. Conc lusion: Before intravascular monitors can be used routinely for clinic al care, reliability, consistency and accuracy will have to be demonst rated in large and widely divergent patient groups. Extravascular on-d emand blood gas analysis is accurate, allows trend monitoring of blood gases and decreases the risk of infection, the therapeutic decision t ime and patient blood loss. As large patient studies are lacking the c linical role of on-line blood gas analysis cannot be clearly delineate d. Copyright (C) 1998 The Canadian Society of Clinical Chemists.