Prediction of post spinal anesthesia hypotension by femoral vein - femoral artery diameter ratio vs inferior vena cava - aorta diameter ratio.

Post spinal anaesthesia hypotension (PSAH) is seen in 15.3 to 33% of patients. In elderly (aged above 50 years), increased resting sympathetic tone and age related alteration in systolic function and diastolic relaxation might exacerbate the decline in cardiac output, increasing the risk of PSAH in these patients. The degree of hypotension and bradycardia induced by spinal anesthesia (SA) is determined by pre operative volume status. Therefore, there is need for assessing pre operative volume status and timely intervention accordingly. Both invasive and non-invasive methods have been explored. Invasive methods include measuring central venous pressure and mean pulmonary artery pressure. Non-invasive approaches involve ultrasonographic measurements of inferior vena cava (IVC), aorta diameter, IVC collapsibility index. This observational, prospective, double blind study will be conducted on a total of 105 patients of either sex, aged 50 years and above, belonging to ASA (American Society of Anesthesiologists) grade I, II & III scheduled for elective surgery under SA. Before giving SA, transverse diameters of femoral vein and femoral artery and anteroposterior diameters of IVC and aorta will be measured using ultrasound. A 2 ml (10 mg) of 0.5% bupivacaine HCl (heavy) and 0.5 ml fentanyl citrate (25 mcg), [total drug volume- 2.5 ml] will be given into subarachnoid space at the level of L3-L4 or L4-L5 intervertebral space in sitting position. After administration of SA, vitals including heart rate, systolic blood pressure(SBP), diastolic blood pressure, mean arterial pressure, respiratory rate, oxygen saturation will be monitored every 2 minutes till 30 minutes. The primary outcome will be measured as the sensitivity and specificity of femoral vein – femoral artery diameter ratio and inferior vena cava – aorta diameter ratio in predicting hypotension in patients aged 50 years and above. The secondary outcome will be measured as correlation between vessel diameter ratios and severity of hypotension episodes and the potential clinical implications of using vessel diameter ratios as predictors of post spinal anesthesia hypotension, including their role in risk stratification.