Spinal anaesthesia is commonly used for surgeries but carries a risk of post spinal anaesthesia hypotension (PSAH) due to decreased systemic vascular resistance and cardiac output. Patients with preexisting hypovolemia and old age are at higher risk due to inherent physiological changes with age. Pre-anaesthetic assessments of preload and afterload can help predict and prevent PSAH. Traditional methods like the passive leg raising test and ultrasonography of the inferior vena cava (IVC) have been used to assess fluid responsiveness. However, these methods are preload dependent and at times not feasible. Newer methods, such as corrected carotid flow time (cCFT), carotid artery peak systolic velocity variation (CAPVV) and internal jugular vein collapsibility index (IJVCI) may offer better predictions of PSAH as they consider both preload and afterload and are less affected by respiration. PSAH can be harmful to patients with limited cardiopulmonary reserve and considering that the elderly heart is very sensitive to preload to maintain cardiac output because of stiff ventricles and blunted reflex tachycardia, it is easy to understand why elderly patients undergoing spinal anesthesia are at increased risk of hypotension, with reported incidences of 25% to 80%. Various preoperative measures have been investigated by researchers to predict PSAH but the evidence is not enough to formulate a conclusive opinion. The intended observational study will be executed in the main operation theatre complex of All India Institute of Medical Sciences, Kalyani after obtaining informed consent from adult patients undergoing surgeries under Spinal Anaesthesia. Overall, 152 patients who are aged more than 60 years undergoing surgeries on lower limb under spinal anaesthesia will be included in the study after applying inclusion and exclusion criteria. All patients will undergo pre anaesthesic ultrasound of neck vessels to determine Carotid blood flow (CBF), cCFT, CAPVV and IJVCI on the right side of the neck using doppler functions. Subsequently, heart rate (HR) and Mean Arterial Pressure (MAP) will be recorded immediately before spinal anaesthesia and defined as baseline readings. The patient will be coloaded with RL infusion of 10ml/kg over 10 minutes. Spinal anaesthesia will be performed at the level of the L3 to 4 or L4 to 5 intervertebral spaces as per standard protocol. MAP will be recorded every 2 minutes for the first 20 minutes immediately after spinal anaesthesia. HR and Oxygen saturation (SpO₂) shall also be recorded at same time intervals. Patients will be given RL infusion of 5 ml/kg/hour as maintenance fluid throughout the intraoperative period. PSAH will be defined as an absolute value of MAP less than 65 mm-Hg or a decrease in MAP by more than 20% from the baseline value. The incidence of hypotension and number of such episodes will be recorded in the first 20 mins after spinal anaesthesia in each patient and accordingly they will be divided into respective groups. First hypotensive episode will be treated with 250 ml of RL bolus and in cases of unresponsiveness or subsequent such episodes, PSAH will be treated with incremental bolus of Phenylephrine 25 mcg as per standard protocol. Atropine 0.5 mg IV will be given if HR falls <50 BPM along with hypotension.