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A Noninvasive Computational Method for Monitoring Compensatory Changes in Obstetrical Patients: The Compensatory Reserve Index
Abstract Number: SA-15
Abstract Type: Original Research
Background: The mother and fetus experience a wide variety of compensatory changes during the peripartum period, as a result of sympathetic blockade, the administration of vasoactive drugs and/or hemorrhage. These physiological changes are being elucidated by recent developments in machine learning, advanced statistical methods and fast computing technology. The Compensatory Reserve Index (CRI) is a computational algorithm that accurately tracks the compensatory phase of central volume loss for high and low tolerant human subjects. CRI requires no reference measurement to normovolemia and is measured on a scale of 1 to 0, where 1 equates to normovolemia and 0 is the point at which hemodynamic decompensation occurs. Values between 1 and 0 indicate the compensatory reserve of the subject.
Hypothesis: CRI accurately measures and trends compensatory changes during the peripartum period.
Methods: Pregnant women undergoing a fetal intervention and/or an operative/vaginal delivery, ages 15-44 years old were enrolled over a 4 month time period. A custom-made pulse oximeter was used to collect continuous photoplethysmographic (PPG) waveforms, which were retrospectively processed by the CRI algorithm to produce beat-to-beat CRI values. Changes in CRI were compared to changes in traditional vital signs during key procedural events, including sympathetic blockade (SB), induction of general anesthesia (GA), hysterotomy, and delivery. Results: 15 patients were enrolled in the study; 3 were excluded for technical reasons. The 8 patients who underwent SB had a pre-SB CRI of 0.86 + 0.1, which decreased to an average nadir CRI of 0.45 + 0.17. Six patients had GA, of which 2 underwent initial SB. Their pre-GA CRI was 0.84 + 0.12, which decreased to 0.51 + 0.23. For all 12 patients, the average CRI just prior to delivery improved to 0.91 + 0.12. Immediately following delivery, however, CRI decreased to 0.66 + 0.19, and then rebounded to > 0.80 during the recovery phase. In comparison, traditional vital signs showed minimal change during these events (Table 1).
Conclusion: The compensatory reserve index algorithm, unlike traditional vital signs, provides real-time, moment-to-moment insight into the physiology of compensation during labor and delivery. Importantly, the underlying technology is based on a learning platform. As a result, the CRI algorithm will become more accurate and more broadly applicable as it is exposed to greater amounts of modeling data.