Accuracy and precision of ScvO2 measured with the CeVOX-device: A prospective study in patients with a wide variation of ScvO2-values

Abstract

Introduction: Central-venous oxygen saturation (ScvO2) 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 ScvO2.

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 ScvO2-values, 12 patients were equipped with a femoral CVC.

Methods: During the 8h study period ScvO2_CeVOX was documented immediately before withdrawal of blood to measure ScvO2 by blood gas analysis (ScvO2_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 ScvO2 (ScvO2_CeVOX_jug) were acceptable with 0.45%, -13.0%, 13.9% and 16.6%, respectively. As supposed, ScvO2 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 ScvO2 by the CeVOX (ScvO2_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 ScvO2_CeVOX-ScvO2_BGA. The amount of the bias |ScvO2_CeVOX-ScvO2_BGA| was independently associated with the amount of the change of ScvO2_CeVOX compared to the initial calibration to ScvO2_BGA_baseline (|ScvO2_CeVOX-ScvO2_BGA_baseline|) as well as with low values of ScvO2_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 |ScvO2_CeVOX-ScvO2_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 |ScvO2_CeVOX-ScvO2_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 ScvO2_BGA. ScvO2_CeVOX accurately estimates ScvO2_BGA in case of stable values. However, intermittent measurement of ScvO2_BGA and re-calibration should be performed in case of substantial changes in ScvO2_CeVOX compared to baseline. Therefore, continuous measurement of ScvO2 with the CeVOX cannot replace ScvO2_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 ScvO2_CeVOX.

Fig 1. Bland Altman plot comparing S_cvO₂_CeVOX_jug to S_cvO₂_BGA derived from measurements with jugular CVC.

S_cvO₂_CeVOX_jug: Central venous oxygen saturation derived from the CeVOX-device. S_cvO₂_BGA: Central venous oxygen saturation derived from blood gas analysis. CVC: Central venous catheter.

Fig 2. Bland Altman plot comparing S_cvO₂_CeVOX_fem to S_cvO₂_BGA derived from measurements with femoral CVC.

S_cvO₂_CeVOX_fem: Central venous oxygen saturation derived from the CeVOX-device. S_cvO₂_BGA: Central venous oxygen saturation derived from blood gas analysis. CVC: Central venous catheter.

Fig 3. Bland Altman plot comparing S_cvO₂_CeVOX to S_cvO₂_BGA derived from all measurements (jugular or femoral CVC).

S_cvO₂_CeVOX: Central venous oxygen saturation derived from the CeVOX-device. S_cvO₂_BGA: Central venous oxygen saturation derived from blood gas analysis. CVC: Central venous catheter.

Fig 4. Correlation of the amount of the bias |S_cvO₂_CeVOX–ScvO2_BGA| with a prediction formula derived from the total datset (n = 120).

S_cvO₂_CeVOX: Central venous oxygen saturation derived from the CeVOX-device. S_cvO₂_BGA: Central venous oxygen saturation derived from blood gas analysis.

Fig 5. ROC curve comparing different predictors of |S_cvO₂_CeVOX–S_cvO₂_BGA| ≥5% in the evaluation group (n = 80).

“Prediction of |bias|”: model predicting |S_cvO₂_CeVOX–S_cvO₂_BGA| which was derived from multiple regression analysis within the evaluation group. ROC: receiver operating characteristic. AUC: area under the curve. S_cvO₂_CeVOX: Central venous oxygen saturation derived from the CeVOX-device. S_cvO₂_BGA: Central venous oxygen saturation derived from blood gas analysis.

Fig 6. ROC curve comparing different predictors of |S_cvO₂_CeVOX–S_cvO₂_BGA| ≥5% in the independent validation group (n = 40).

Prediction of |bias|: model predicting |S_cvO₂_CeVOX–S_cvO₂_BGA| which was derived from multiple regression analysis within the evaluation group. ROC: receiver operating characteristic. AUC: area under the curve. S_cvO₂_CeVOX: Central venous oxygen saturation derived from the CeVOX-device. S_cvO₂_BGA: Central venous oxygen saturation derived from blood gas analysis.