Evaluation of patient volemia arriving at a medical service today still represents a challenge for specialists, especially in those who need surgical and anesthetic intervention. One of the most common systemic side effect to anesthesia is hypotension. Spinal Anesthesia-Induced Hypotension (SAIH) because of sympathetic blockade is most frequently cited as a complication of subarachnoid anesthesia, its severity being influenced by the patient's volemic state. The aim of this literature review is to analyze if „routine” preanesthetic preloading reduces the incidence of SAIH in patients undergoing spinal anesthesia, also to emphasize the efficacy of preanesthetic assessment of the IVC/Ao (Inferior Vena Cava/Abdominal Aorta) Index measured by ultrasound in determination of patients’ volemia.