Accuracy and precision of S(cv)O(2) measured with the CeVOX-device: A prospective study in patients with a wide variation of S(cv)O(2)-values

INTRODUCTION: Central-venous oxygen saturation (S(cv)O(2)) is a key parameter of hemodynamic monitoring and has been suggested as therapeutic goal for resuscitation. Several devices offer continuous monitoring features. The CeVOX-device (Pulsion Medical Systems) uses a fibre-optic probe inserted through a conventional central-venous catheter (CVC) to obtain continuous S(cv)O(2). OBJECTIVES: Since there is a lack of studies validating the CeVOX, we prospectively analyzed data from 24 patients with CeVOX-monitoring. To increase the yield of lower S(cv)O(2)-values, 12 patients were equipped with a femoral CVC. METHODS: During the 8h study period S(cv)O(2)_CeVOX was documented immediately before withdrawal of blood to measure S(cv)O(2) by blood gas analysis (S(cv)O(2)_BGA) 6min, 1h, 4h, 5h and 8h after the initial calibration. No further calibrations were performed. RESULTS: In patients with jugular CVC (primary endpoint; 60 measurements), bias, lower and upper limits of agreement (LLOA; ULOA) and percentage error (PE) of the estimate of S(cv)O(2) (S(cv)O(2)_CeVOX_jug) were acceptable with 0.45%, -13.0%, 13.9% and 16.6%, respectively. As supposed, S(cv)O(2) was lower in the femoral compared to the jugular measurements (69.5±10.7 vs. 79.4±5.8%; p<0.001). While the bias (0.64%) was still acceptable, LLOA (-23.8%), ULOA (25.0%) and PE (34.5%) were substantially higher for femoral assessment of S(cv)O(2) by the CeVOX (S(cv)O(2)_CeVOX_fem). Analysis of the entire data-pool with jugular as well as femoral CVCs allowed for a multivariate analysis which demonstrated that the position of the CVC per se was not independently associated with the bias S(cv)O(2)_CeVOX—S(cv)O(2)_BGA. The amount of the bias |S(cv)O(2)_CeVOX–S(cv)O(2)_BGA| was independently associated with the amount of the change of S(cv)O(2)_CeVOX compared to the initial calibration to S(cv)O(2)_BGA_baseline (|S(cv)O(2)_CeVOX—S(cv)O(2)_BGA_baseline|) as well as with low values of S(cv)O(2)_BGA_baseline. Furthermore, increasing time to the initial calibration was associated to the amount of the bias with borderline significance. A statistical model based on |S(cv)O(2)_CeVOX—S(cv)O(2)_BGA_baseline| and “time to last calibration” derived from an evaluation dataset (80 of 120 datasets, 16 of 24) provided a ROC-AUC of 0.903 to predict an amount of the bias |S(cv)O(2)_CeVOX–S(cv)O(2)_BGA| ≥5% in an independent validation group (40 datasets of 8 patients). CONCLUSION: These findings suggest that the CeVOX device is capable to detect stability or instability of S(cv)O(2)_BGA. S(cv)O(2)_CeVOX accurately estimates S(cv)O(2)_BGA in case of stable values. However, intermittent measurement of S(cv)O(2)_BGA and re-calibration should be performed in case of substantial changes in S(cv)O(2)_CeVOX compared to baseline. Therefore, continuous measurement of S(cv)O(2) with the CeVOX cannot replace S(cv)O(2)_BGA in instable patients. On the other hand, CeVOX might be useful for the monitoring of stable patients as a pre-test tool for more differentiated monitoring in case of changes in S(cv)O(2)_CeVOX.