: Multiple attempts during subarachnoid block can result in complications like post dural puncture headache, lower back pain and cause discomfort to the patient, apart from being time consuming. Although, anatomical knowledge and technical skills are important, presumed prearrangement of the skin to subarachnoid space depth (SSD) may lead to the correct placement of the spinal needle. This allows for less traumatic and fewer repetitive attempts for spinal anesthesia. The palpation of bony landmarks required to successfully perform lumbar punctures (LPs) can be masked in 33% of overweight patients and 68% of patients with obesity, due to overlying soft tissue and can lead to LP failure rate of 19%. In a patient, the SSD varies considerably at different levels of the spinal cord. It also varies from patient to patient at the same vertebral level as per age, sex and body mass index (BMI). 

The rationale behind doing this study is to assess which method is more accurate to determine the SSD so as to minimize repeated attempts for spinal anaesthesia especially in overweight patients.

 The study is going to assess the SSD in a population with BMI>25kg/m2 with anthropometric measurements, ultrasonography and actual depth by needle insertion.