Introduction
Less invasive measurement of central venous O2 saturation(ScvO2) has shown to be a valuable alternative to the determination of mixed venous O2 saturation for monitoring of O2 supply/demand [1,2]. The aim of this study was to compare ScvO2 measured continuously by the new CeVOX (Pulsion Medical System, Munich, Germany) device (CScvO2) with ScvO2 determined by blood gas co-oximetry (BScvO2).
Methods
Ten ASA III patients undergoing elective off-pump coronary artery bypass grafting were studied during the operation (OP) and during their ICU stay. In addition to the standard hemodynamic monitoring according to institutional policy, a CeVOX fiber-optic probe was introduced into a standard central venous catheter placed via internal jugular vein access. OP and ICU measurement started after in-vivo calibration of CeVOX. BScvO2 and CScvO2 readings were recorded at intervals of 30 min during OP and of 120 min during ICU. Data were statistically analyzed using Bland-Altman analysis, Pearson correlation and t test for the periods during OP, ICU, a set of three consecutive measurements during OP immediately after calibration (OPcal) and 4 hours later (OP4h) as well as immediately after calibration on the ICU (ICUcal) and 14 hours later (ICU14h). Trend analysis was performed, calculating differences (Δ) between consecutive measurements. P < 0.05 was considered significant.
Results
One hundred and twenty-nine matched sets of data were obtained (OP:n = 78, ICU: n = 51) with a wide range of ScvO2 values (BScvO2 = 48.0–91.0%, CScvO2 = 49.0–94.0%). The OP observation time was 4.0–6.5 hours and the ICU measurement sequence was 14.0–20.0 hours. Bland-Altman analysis revealed an overall mean bias ± 2SD (limits of agreement) of-0.7 ± 7.8% for CScvO2 – BScvO2 during OP and -1.1± 11.6% during ICU (Fig. 1). There was no significant difference between CScvO2 and BScvO2 (OP: P = 0.120, ICU: P = 0.167). The correlation coefficient(r2) for CScvO2 vs BScvO2 was 0.885 (OP) and0.592 (ICU). Statistics for OPcal' OP4h and ICUcal were comparable, whereas for ICU14h the bias ± 2SD increased and r2 decreased (Table 1). Trend analysis showed no significant difference (OP: ΔBScvO2 = -1.3 ± 9.0%, ΔCScvO2 = -1.1 ± 8.6%, P = 0.663; ICU: ΔBScvO2 = -0.4 ± 6.8%, ΔBScvO2 = -0.4 ± 5.8%, P = 0.828).
Figure 1.
Table 1.
| OPcal | OP4h | ICUcal | ICU14h | |
|---|---|---|---|---|
| Mean bias ± 2SD (%) | -0.3 ± 7.2 | -0.1 ± 8.4 | -0.7 ± 8.6 | -1.9 ± 14.0 |
| r2 | 0.849 | 0.853 | 0.832 | 0.358 |
Conclusion
These preliminary results indicate that ScvO2 can be reliably assessed by CeVOX. Scheduled recalibration at intervals <14 hours may be mandatory.