This study will establish the feasibility and preliminary validity of real-time oxygen delivery index (DO₂i) monitoring using noninvasive hemoglobin (SpHb, Masimo) and minimally invasive cardiac output (FloTrac, Edwards) in cardiac surgery patients.
Adults ≥ 18 years undergoing cardiac surgery
Placement of pulmonary artery catheter with continuous cardiac output (CCO) as part of routine clinical care
Placement of arterial line with FloTrac as part of routine clinical care
Availability of ≥ 3 arterial blood gas samples at specified timepoints
Mechanical circulatory support planned or in use (IABP, Impella, ECMO)
Patients without BOTH pulmonary artery catheter with CCO and arterial line with FloTrac
Patients who are Research Opt-Out
Adults undergoing cardiac surgery
Case-control
Prospective
SpHb monitor
DeviceThe SpHb monitor is an FDA approved device being used according to its approved indications. No additional invasive procedures, blood draws, or interventions are performed for research purposes.
Agreement Between SpHb-Based and Pulmonary Artery Catheter Oxygen Delivery Index
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%.
Directional Agreement for Changes in Oxygen Delivery Index
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.
Correlation Between Oxygen Delivery Index and Arterial Lactate
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.
Agreement Between FloTrac and Swan-Ganz Cardiac Index
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%.
Impact of Baseline SpHb Calibration on Agreement
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.
Major Adverse Cardiac Events (Exploratory)
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.
Acute Kidney Injury (Exploratory)
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).
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