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Peripartum: Utilizing the Compensatory Reserve Index to predict changes in blood pressure with regional anesthesia
Abstract Number: S4A-4
Abstract Type: Original Research
Introduction: Complete neuraxial sympathetic blockade decreases vascular tone at and below the level of the block by 30-40%, which reduces systemic vascular resistance and often times results in a drop in blood pressure . The Compensatory Reserve Index (CRI) is a new adjunctive cardiovascular status indicator that reflects changes in intravascular volume relative to the individual’s response to hypovolemia . We hypothesized that low CRI values prior to regional anesthesia would be associated with the percent decrease in mean arterial blood pressure (MAP) post-regional anesthesia in parturients.
Methods: An investigational, noninvasive CipherOX CRI™ M1 monitor (Flashback Technologies, Louisville CO) was applied to enrolled parturients undergoing fetal interventions or operative delivery. CRI values, medications, vital signs, and fluid administration were recorded. A multivariable linear regression model was fit with the percent change in MAP immediately preceding regional anesthesia to minimum post-regional anesthesia MAP as the outcome. Minimum CRI pre-regional was the primary predictor and the model was adjusted for procedure type and total phenylephrine dosing (mcg/kg) prior to minimum MAP.
Results: Seventy-nine subjects, including thirty-four operative deliveries and forty-five fetal interventions, were included for analysis. Median minimum CRI and MAP prior to regional anesthesia were 0.26 (Interquartile range (IQR): 0.11, 0.42) and 89.7 (IQR: 84.0, 101.3), respectively. Median percent change in MAP after sympathetic blockade was 24.3% (IQR: 15.0, 35.1). After adjusting for procedure type and total phenylephrine administered prior to minimum MAP, minimum CRI between sitting and regional was significantly associated with the percent change in MAP from before to after placement of a regional neuraxial block (p=0.009). For every 0.10 decrease in minimum CRI, the percent MAP change increased by 2.4% (95% Confidence Interval (CI): 0.64%, 4.1%). Patients who presented for a cesarean delivery had a 6% (95% CI: -0.4, 12.3) higher change in MAP compared to those who presented for a fetal intervention (p=0.07).
Conclusion: The Compensatory Reserve Index provides real-time, noninvasive insight into hemodynamic and central volume changes that occur with regional anesthesia in parturients. CRI may dramatically change how central volume status is assessed and monitored during the peripartum period and allow for optimization prior to regional anesthesia, including fluid resuscitation and early administration of pressors.
 Langesaeter E, Dyer RA. Maternal hemodynamic changes during spinal anesthesia for cesarean section. Curr Opin Anaesthesiol 2011; 24:242-8
 Moulton S, Mulligan J, Santoro MA, Bui K, Grudic G, MacLeod D: Validation of a non-invasive monitor to continuously trend individual responses to hypovolemia. J Trauma Acute Care Surg 2017; 83(1 Suppl 1):104-111