Monitoring of central venous oxygen saturation versus mixed venous oxygen saturation in critically ill patients

Abstract

Continous monitoring of mixed venous (SvO2) and central venous (ScO2) oxygen saturation was compared in 7 critically-ill patients (Apache II score: 19±2.1) to determine whether or not information derived from ScO2 were reliable in clinical practice. Patients were catheterized with both a pulmonary artery (PA) and a central venous (CV) catheter, each of them mounted with fiberoptic sensors (Opticath PA Catheter P7110 and Opticath CV Catheter U440, Abbott). A total of 580 comparative measurements were obtained during periods without and with therapeutic interventions (drug-titration, bronchial suction, use of PEEP, changes in FiO2...). The systematic error between the 2 measurement techniques was 0.6% and 0.3% in periods with and without therapeutic interventions, respectively. The variability between the 2 techniques was 10% for both periods. Differences between the values were ≧5% in 49% of values during periods of stability and in 50% of values during periods with therapeutic interventions. There were poor correlations between the values during periods without (r=0.48) and with therapeutic interventions (r=0.62). Better, but still less than ideal, correlations were obtained with changes in SvO2 and ScO2 during periods without (r=0.70) and with therapeutic interventions (r=0.77). Although there is a need to develop a simple technique to monitor mixed venous oxygen saturation, the present study indicates that ScO2 monitoring was not reliable in the study patients. © 1992 Springer-Verlag.