Comparative assessment of Subclavian vein versus Inferior Vena Cava diameter and collapsibility index for predicting post induction hypotension in obese patients undergoing elective surgeries under general anaesthesia: a prospective observational study.

After Institutional Ethics Committee approval, written informed consent will be obtained from patients. Demographic data, diagnosis, fasting hours, BMI, and comorbidities will be recorded in a patient proforma.In the preoperative area, ultrasound guided measurements of maximum and minimum diameters of the subclavian vein (SCV) and inferior vena cava (IVC) will be taken three times each in supine patients during spontaneous normal breathing. These will be performed by a qualified anesthesiologist using a portable color Doppler ultrasound machine (Model Edge II, FUJIFILM Sonosite Inc, USA).For SCV, a high frequency linear transducer will be placed perpendicular to the clavicles long axis in the supine position, scanning the lateral third of the clavicle for a short axis view. Patients breathe normally, and minimum (dSCVmin) and maximum (dSCVmax) diameters at end expiration and inspiration will be measured in M mode during the same cycle.For IVC, a curved transducer will be placed subxiphoid with the pointer cephalad, moved right and cranial for a long axis view entering the right atrium. Pulse wave Doppler differentiates IVC from aorta. Minimum (dIVCmin) and maximum (dIVCmax) diameters at end inspiration and expiration will be measured in M mode. Mean values from three readings calculate collapsibility index (CI) as (Maximum diameter minus minimum diameter times 100 divided by maximum diameter).Time from probe placement to measurement and feasibility (ability to visualize and measure) will be noted. Data collected via case record form.In the operating theater, standard ASA monitors (ECG, pulse oximetry, NIBP) record baseline heart rate, NIBP, and SpO2. General anesthesia induction uses midazolam 005 mg/kg IV, fentanyl 2 mcg/kg IV, propofol 2 mg/kg IV, vecuronium 01 mg/kg IV; doses noted. The inducing anesthesiologist is blinded to preoperative findings. Loss of consciousness confirmed by vocal response/jaw thrust/eyelash reflex.Vitals monitored continuously; NIBP every 1 minute for 5 minutes, then every 2 minutes for 20 minutes, then every 5 minutes. Postinduction hypotension defined as MAP below 65 mmHg or over 20 percent drop from baseline. Hypotensive episodes treated with fluids/vasopressors at discretion; number and duration noted.Primary objective: Compare diagnostic accuracies of SCV/IVC diameters and CI for predicting postinduction hypotension in obese patients undergoing elective surgery.