Inferior vena cava ultrasound versus passive leg raising test in guiding fluid administration in surgical patients prior to spinal anaesthesia: a post-hoc analysis of the ProCRHYSA randomized trial. PROtocolized Care to Reduce HYpotension after Spinal Anaesthesia https://www.medrxiv.org/content/10.1101/2023.05.22.23290367