Validation and Feasibility of Noninvasive Oxygen Delivery Index Monitoring in Cardiac Surgery Patients

Bias and 95% limits of agreement between monitor-derived DO₂i (calculated from continuous SpHb and FloTrac cardiac index) and pulmonary artery catheter DO₂i (calculated from arterial blood gas hemoglobin and Swan-Ganz cardiac index), analyzed using Bland-Altman method with mixed-effects modeling to account for repeated measures. Agreement is considered acceptable if percentage error is <30%.

Four-quadrant concordance rate (with 15% exclusion zone) for directional changes in DO₂i between consecutive timepoints. Concordance is defined as agreement in direction of change (increase vs decrease) between monitor-derived and gold-standard DO₂i measurements. Scores range from 0- 100%, with higher percentages indicating better directional agreement.

Pearson or Spearman correlation coefficient between DO₂i (both monitor-derived and gold- standard) and simultaneously measured arterial lactate concentration. Correlation coefficients range from -1 to +1, with negative values indicating inverse relationship between DO₂i and lactate.

Percentage error between FloTrac arterial pressure-based cardiac index and Swan-Ganz thermodilution continuous cardiac index. Percentage error is calculated as (1.96 × SD of differences) / mean cardiac index × 100%. Agreement is considered acceptable if percentage error is <30%.

Comparison of limits of agreement before and after in vivo SpHb calibration (baseline- adjusted SpHb using first arterial blood gas hemoglobin value as reference). Measured as change in bias and 95% limits of agreement between uncalibrated and baseline-calibrated SpHb-based DO₂i compared to gold standard.

Percentage of planned timepoints with valid SpHb signal defined by perfusion index (PI) ≥ 0.5. Scores range from 0-100%, with 100% indicating valid signal at all timepoints.

Minimum perfusion index value associated with acceptable SpHb accuracy, defined as SpHb bias within ±1 g/dL of arterial blood gas hemoglobin. Perfusion index values range from 0-20%, with higher values indicating better peripheral perfusion.

Composite endpoint including all-cause mortality, myocardial infarction (elevated troponin with ECG changes or clinical symptoms), stroke (new neurologic deficit with imaging confirmation), or urgent revascularization.

AKI defined and staged using KDIGO criteria based on postoperative serum creatinine changes: Stage 1 (1.5-1.9× baseline or ≥0.3 mg/dL increase), Stage 2 (2.0-2.9× baseline), Stage 3 (≥3× baseline or ≥4.0 mg/dL or initiation of renal replacement therapy).