Hemodynamic monitoring and fluid protocols
subclavian vein collapsibility
Pre-operative fasting was initiated 8 h before surgery, and water intake was permitted until 2 h before surgery. Due to insufficient time for subclavian vein ultrasonography (SCVUS) during spinal anesthesia (the co-loading protocol), we conducted a SCVUS-based preloading protocol (SCVUS group) and compared it with the empirical fixed-volume fluid preload approach (control group).Upon arrival in the operating room, standard non-invasive anesthesia monitoring, including continuous ECG, non-invasive blood pressure measurements, and oxygen saturation of the pulse (Infinity C500; Dräger Medical, Lübeck, Germany) was started and an 18-G intravenous line was placed. Before implementation of the fluid protocol, patients lay supine in a calm atmosphere for at least 5 min to achieve the proper hemodynamic condition. Treatment allocation was performed by a nurse. Anesthesiologists, researchers, and study participants were blinded to allocation. Subsequently, either the fixed-volume preloading or SCVUS-directed procedure was started before spinal anesthesia by another anesthesiologist who did not take part in anesthetic care.A single anesthesiologist who was properly trained in ultrasonography performed all SCV measurements with patients in the supine position using GE ultrasonography equipment (GE Medical Systems Ultrasound & Primary Care Diagnostics LLC) before proceeding to spinal anesthesia.Right SCV diameters were measured using an M-mode high-frequency (6–13 MHz) linear array probe. In order to get the best cross-sectional picture of the vein, the probe was positioned beneath the proximal region of the midpoint of the clavicle perpendicular to the long axis of the SCV [
B-mode and M-mode ultrasonography to evaluate SCV with the subcostal view. The SCVCI was calculated as follows: SCVCI=(dSCVmax–dSCVmin)/dSCVmax×100%. The result therefore is expressed as percentages. SCV, subclavian vein; SCVCI, subclavian vein collapsibility index; dSCVmax and dSCVmin, the maximum and minimum antero-posterior diameters of the subclavian veinA quick infusion of Ringer’s solution (10 mL/kg) was administered to women in the control group within 15 min. Women in the SCVUS group with SCVCI > 38% were considered to have a positive fluid response [