Background: Since its first introduction in 1898 by Bier, Spinal anesthesia has been performed using the anatomical landmark guided approach. Despite being useful, the landmark technique doesn't take into account anatomical variations, spine abnormalities or age-related changes in the lumbar spine as seen in elderly, obese or pregnant patients and thus can lead to incorrect identification of a certain interspace. Neuraxial ultrasonography has been introduced as a technique to allow the operator to preview spinal anatomy, identify the midline, determine the interspace and guide the needle insertion site and trajectory. It was found to be a feasible and promising technique that can result in successful cerebrospinal fluid acquisition where other methods have failed. While pre-procedural Ultrasound has been used by many studies to identify the right epidural or subarachnoid spaces and have an idea about the angle of needle insertion, it remains a blind technique. Real-time ultrasound guided technique was found to improve the limitations of the pre-puncture ultrasound guided techniques by direct, real-time visualization of the needle trajectory. In spinal anesthesia, a midline approach has been the most common technique used for needle insertion. However, this approach is often technically difficult in the geriatric population because of poorly palpable surface landmarks, lumbar scoliosis, marked thoracic kyphosis, degenerative changes and inability to flex the lumbar spine in the sitting position. While the parasagittal oblique approach tends to provide a better sonographic window into the vertebral canal than the midline approach, it is still not evident whether it will lead to an easier paramedian needle insertion. In the literature, there are no studies directly comparing the paramedian transverse and parasagittal oblique approaches in the performance of real time ultrasound guided spinal anesthesia.

Specific Aim: The aim of this study is to find out the optimal approach to perform spinal anesthesia under real time ultrasound guidance in the elderly population. Thus, investigators will compare real time ultrasound-guided paramedian approach using parasagittal oblique view with real time ultrasound guided paramedian approach using the paramedian transverse median view. The aim is thus to adopt a real time ultrasound guided technique that will result in an easier access to the subarachnoid space in patients with difficult anatomy and results in better patient satisfaction and less discomfort.

Methodology and analysis: In a prospective randomized observational study, 84 patients scheduled for surgery amenable to spinal anesthesia, aged more than 65 years, with American Society of Anesthesiologists physical status 1 to 3 will be assigned to receive spinal anesthesia to one of two treatment groups: real time ultrasound-guided parasagittal oblique technique (group RTU-PO) or Real time ultrasound-guided paramedian transverse technique (group RTU-T). Ultrasonography of the lumbar spine and Real time spinal blockade will be performed by the experienced anesthesiologist. Patients in both groups will have an ultrasound scan of the lumbar spine to measure the depth of the dura, to specify and guide the needle insertion site and trajectory. The primary outcome is the rate of successful dural puncture on the first needle insertion attempt under real time ultrasound guidance. Normally distributed data will be summarized as mean ± SD and nonnormally distributed data will be summarized as median \[interquartile range\].

Significance: Investigators believe that real time US-guided technique is a superior modality of performance of spinal anesthesia. However, investigators would like to evaluate which approach will be better for the acquisition of cerebrospinal fluid in elderly patients. Investigators think that this study would have an impact on current practice in term of introducing real time ultrasound guided technique into everyday practice and determining the best approach to perform a successful neuraxial block in a patient with a suspected difficult back.