Comparative evaluation of 2 fiber optic catheters for the continuous measurement of Svo2]

Nineteen intensive care patients with shock and acute respiratory failure were studied using two different fiber-optic catheters used for the continuous measurement of mixed venous blood oxygen saturation (SVO2). In groupe I patients (n = 11), a Swan-Ganz catheter with optic fibres emitting light characterized by three different wavelengths was used (Opticath Oximetrix). In groupe II patients (n = 8), a Sat-one Edwards catheter was used instead (only two different wavelengths). All the patients were studied in the early stages of shock, once all the calibration procedures had been carried out. An increase in FIO2, using PEEP, fluid replacement therapy and vasoactive drugs or diuretics all improved the cardio-respiratory status of each patient. After each new therapeutic procedure, SVO2 was measured in blood samples obtained from these catheters, and from the pulmonary artery (to give the reference value, using an OSM3 Hemoximeter). Over a period of 1.5 to 6 h, 119 measurements were carried out in Group I, and 91 in Group II. The correlation coefficient was higher with the Oximetrix catheter than with the Edwards one (r = 0.970 and 0.855 respectively; p less than 0.001). Moreover, the 24 h spontaneous drift of the former catheter was less than that of the latter (+3.3 +/- 3.1% vs. +9.3 +/- 7%, p less than 0.05). This study showed that a catheter with optic fibres emitting a light with three wavelengths is more accurate than one emitting only two for the measurement of changes in SVO2 in critically ill patients.