Stroke-Volume Response to a Standardized Fluid Challenge in Healthy Term Parturients: A Prospective Pilot Study

Background: Hemodynamic adaptation to pregnancy is characterized by substantial interindividual variability, which may influence the cardiovascular response to fluid administration. However, the distribution of stroke-volume responses to a standardized fluid challenge in healthy term pregnancy remains poorly characterized. Objectives: This study aimed to characterize the magnitude and distribution of the stroke-volume response to a standardized crystalloid fluid challenge in healthy term parturients and to determine the proportion exceeding the protocol-defined 10% response threshold. Methods: This prospective interventional pilot study reports the hemodynamic response to the fluid-challenge component of a broader Ethics Committee-approved prospective interventional protocol involving a medical device. Participants were recruited by convenience sampling when an anesthesiologist involved in the study protocol was available. Healthy women with singleton term pregnancies scheduled for elective cesarean delivery were studied before spinal anesthesia in a 30° dorsal head-up supine position. After placement of an 18-G peripheral intravenous cannula and 5 min of ClearSight™ stabilization, a 250-mL crystalloid fluid challenge was administered under continuous non-invasive hemodynamic monitoring. Stroke volume (SV) was recorded every 20 s. Baseline SV was defined as the mean of the last three valid pre-challenge measurements, and the response was quantified as the maximum mean of three consecutive valid SV measurements during the first 10 min after challenge initiation. The percentage change in SV (ΔSV) was analyzed as a continuous variable; the protocol-defined 10% threshold was used to describe the proportion of participants exhibiting a response above this level. Results: Thirty-five participants had complete hemodynamic recordings suitable for the standardized analysis. The median ΔSV was 6.48% (IQR 1.21–13.91%). Thirteen of 35 participants exceeded the protocol-defined 10% threshold, corresponding to a proportion of 37.1% (95% CI 21.5–55.1%). Conclusions: Healthy term parturients exhibited substantial interindividual variability in SV response to a 250-mL crystalloid fluid challenge under the standardized study conditions. The continuous distribution of ΔSV and the uncertainty surrounding the proportion exceeding the protocol-defined threshold do not support interpretation of fluid responsiveness as a discrete physiological phenotype. These exploratory findings require confirmation in larger, prospectively powered studies before their potential relevance to individualized perioperative fluid management can be established. These findings provide exploratory physiological evidence of interindividual variability in maternal preload response and support further investigation of whether individualized hemodynamic assessment may contribute to personalized perioperative management in obstetric anesthesia.