Intensive Care Med (1992) 18:101 - 104 IntensiveCare Medicine 9 Springer-Verlag 1992 Monitoring of central venous oxygen saturation versus mixed venous oxygen saturation in critically ill patients C. Martin, J.-P. Auffray, C. Badetti, G. Perrin, L. Papazian and F. Gouin Department of Anesthesia and Intensive Care, H6pital Sainte Marguerite, Marseille, France Received: 15 April 1991; accepted: 31 December 1991 Abstract. Continuous 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 P 7110 and Op- ticath CV Catheter U440, Abbott). A total of 580 com- parative measurements were obtained during periods without and with therapeutic interventions (drug-titra- tion, bronchial suction, use of PEEP, changes in FiO2...). The systematic error between the 2 measure- ment 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 interven- tions (r = 0.62). Better, but still less than ideal, correla- tions were obtained with changes in SvO 2 and ScO2 dur- ing periods without (r = 0.70) and with therapeutic in- terventions (r = 0.77). Although there is a need to develop a simple technique to monitor mixed venous oxygen saturation, the present study indicates that ScO 2 monitoring was not reliable in the study patients. Key words: Central venous catheter - Central venous ox- ygen saturation - Mixed venous oxygen saturation - Pulmonary artery catheter Continuous monitoring of mixed venous oxygen satura- tion SvO2 has recently been made possible with the use of PA catheters mounted with fiberoptic sensors [1- 5]. Modifications in SvO z are dependent on the effec- tiveness of air-blood gas exchange in the lung, cardiac output, tissue oxygen uptake and oxyhemoglobin dis- sociation. In critically ill patients there has been a con- siderable interest in the relationship of SvOz to car- diorespiratory function [6, 7]. However the risk/benefit ratio of PA catheters is still a matter for vigorous con- troversies [8, 9]. On the other hand CV catheters are routinely inserted in intensive care patients for monitor- ing of CV pressure and for administration of artificial parenteral nutrition. Monitoring of central venous ox- ygen saturation (SCO2) would be an interesting alter- native for SvOz monitoring as far as similar information is given by both methods. The aim of this study was to compare simultaneous measurements of SvOa and ScO2 obtained from PA and CV catheters inserted in critically ill patients. A special attention was paid to periods of instable clinical condi- tions (bronchial suctions, modifications in inspired ox- ygen fraction (FiO2), treatment of septic shock...). A difference < 5~ saturation was chosen to decide that the 2 methods of measurements were interchangeable. Materials and methods In a prospective study, 7 consecutive patients requiring monitoring of PA pressure and parenteral nutrition were catheterized with an Op- ticath | PA Catheter P 7110, 7.5 F (Abbott) and an Opticath CV Cathe- ter U440, 4 F (Abbott). The protocol was approved by the Human In- vestigation Committee of our institution. Prior to insertion, both cathe- ters were calibrated in vitro following the manufacturer's instructions. The central venous catheters were inserted in the right internal jugular vein and the pulmonary artery catheters in the right axillary vein follow- ing standard aseptic technique. All these patients were receiving con- trolled mechanical ventilation, sedated with phenoperidine and paralyz- ed with vecuronium bromide and no local anesthesia was used. The PA catheter was positioned following standard procedures and advanced until a typical wedge pressure was obtained with the balloon inflated with 1.5 ml air. Obtaining a typical PA tracing with the balloon deflated was carefully checked in each patient. Central venous catheters were positioned in the lower part of the Superior Vena Cava, Correct posi- tions of catheter tips were confirmed in each patient by a chest X-ray. Each catheter was connected to a venous oxygen saturation monitor (Oximetric 3 | Abbott) that had the capacity to continuously and simul- taneously display SvO 2 and ScO 2 values. Monitors were recalibrated every morning using a Co-oximeter (Instrumentation Laboratory).