Spinal anaesthesia is frequently used in daily clinical practice. Post spinal anaesthesia  hypotension (PSAH) is a common side effect with an incidence of 15.3% to 33% that may result in organ hypoperfusion and ischaemic events^1,2.The two fundamental factors in the pathogenesis of PSAH are sensory block level at or above T5 and age more than 40 years³.Patients’ susceptibility to intra-operative hypotension can also be influenced by the pre-operative volume status that may differ according to comorbidities, physical status, pre-operative medications and fasting⁴.

PSAH due to spinal blockade is principally a consequence of diminished systemic vascular resistance after blockade of preganglionic sympathetic fibers. Many attempts have been tried to prevent PSAH, such as intravenous  volume  preload  or  prophylactic vasopressors. However, fluid co-load has been proved to lower the incidence of PSAH and significantly decrease the vasopressor requirements. At the same time, empirical volume loading carries the potential of volume overload, particularly in patients with cardiac disease. Consequently, the search for predictors of PSAH is becoming mandatory to avoid blind volume loading and reserve it only for patients who are expected to develop PSAH.

Several methodologies have been tried with a specific goal to predict PSAH, including heart rate variability (HRV), passive leg raise test and perfusion index^5,6,7.Although some studies found a positive predictive value of HRV with high sensitivity and specificity for PSAH, others concluded that it was not a reliable predictor as it can be influenced by numerous factors such as diabetes mellitus, ischaemic heart disease, antihypertensive medications, anxiety and spontaneous respiration⁵.

Various parameters have been investigated recently to estimate the pre-operative intravascular volume status. Sonographic determination of inferior vena cava collapsibility index (IVCCI) and IVC to aorta diameter index (IVC : Ao index) has been introduced into clinical practice for the assessment of intravascular volume in many studies and reported to be easy reliable and noninvasive  for evaluating the volume status. So, the aim of this study is to evaluate the efficacy of both pre-operative IVCCI and IVC : Ao index for predicting the occurrence of PSAH.