Effects of Phenylephrine Administration on the Circulatory Dynamics of Patients with Hypotension Due to Bleeding During Surgery, Specifically Left Ventricular End-Diastolic Volume, Effective Arterial Elastance, and Left Ventricular End-Systolic Elast

<b>Background/Objectives</b>: Under general anesthesia, maintaining patients' blood pressure (BP) is important to prevent organ ischemia. When bleeding occurs, it is sometimes difficult to increase BP with boluses of fluids or transfusions, and vasoconstrictors must be administered. This study investigated circulatory dynamic changes in patients who bled during surgery and were administered phenylephrine, particularly left ventricular end-diastolic volume (EDV), effective arterial elastance (Ea), and left ventricular end-systolic elastance (Ees), calculating each value from the left ventricular-arterial coupling (Ees/Ea). <b>Methods</b>: We calculated Ees/Ea using electrocardiograms, arterial pressure waveforms, and phonocardiograms using an esophageal stethoscope. We investigated the changes in patients' EDV, Ea, and Ees during two periods: phenylephrine administration and after BP elevation. <b>Results</b>: The seven participants comprised three men and four women. Between the two periods, linear mixed-model analysis revealed that mean arterial pressure (MAP), Ea, and Ees significantly increased over time (MAP; β = 8.7, <i>p</i> < 0.01, Ea; β = 0.22, <i>p</i> < 0.05, Ees; β = 0.73, <i>p</i> < 0.05), while no significant changes were observed in other parameters such as heart rate and EDV. Conventional parameters demonstrated that stroke volume variation significantly decreased (β = -2.0, <i>p</i> = 0.01), systemic vascular resistance index significantly increased (β = 200, <i>p</i> < 0.01), while no significant change was observed in cardiac index (β = -0.03, <i>p</i> = 0.7). In patients administered phenylephrine due to BP decrease from bleeding, significant changes in afterload and cardiac contractility occurred without changes in preload. <b>Conclusions</b>: Our noninvasive method for calculating EDV, Ea, and Ees can be valuable for monitoring hemodynamics under anesthesia.