An observational study to identify the intervertebral space for the ease of spinal anaesthesia in four different sitting positions

Spinal anesthesia is a neuraxial anesthesia technique in which local anesthetic is placed directly in the intrathecal space (subarachnoid space). The subarachnoid space houses sterile cerebrospinal fluid (CSF), the clear fluid that bathes the brain and spinal cord. There are roughly about 130 to 140 mL of CSF in an adult human which continually cycles throughout the day. Approximately 500 mL of CSF gets produced daily. Spinal anaesthesia is the most commonly used  anaesthetic technique for patients undergoing surgical procedure like infra-umbilical, perineum, pelvicgirdle. Spinal anaesthesia is useful in patients where severe respiratory disease or a difficult airway increases the risk of general anaesthesia.

Patient positioning during administration of spinal anesthesia is very important. Poor positioning may cause repeated spinal needle insertions and increase the risk of back pain, post-dural puncture headache (PDPH), epidural hematoma, and neural trauma. The sitting position is frequently used for patients undergoing spinal anesthesia, especially when low lumbar and sacral levels of sensory anesthesia are needed for the surgical procedure. The most important point for performing a neuroaxial block in a sitting position is reducing lumbar lordosis, resulting in easier access to the intervertebral space; on the other hand, lumbar flexion pushes the theca sac into a more superficial position

It is sometimes difficult for some patients to optimally flex their hips and knees making traditional position for induction of spinal anaesthesia difficult to achieve.Hence, there are a few  different modified sitting positions for this purpose like forward bending position(hamstring stretch position),squatting position and crossed-leg sitting position.

The traditional sitting position (TSP) is the most common position for spinal or epidural anesthesia where the patient sits on the operating table, with both feet placed on a stool, and both hips and knees maximally flexed . Four decades ago, a new sitting position was introduced to reduce lumbar lordosis for “easier” spinal puncture; this position involved maximum extension of the knees, adduction of the hips, and forward bending. Based on this idea, modified sitting positions have been introduced for spinal or epidural anesthesia. In these positions, the patients are sat up on the operating table, but the legs remain on the table, which is different from the TSP. In the hamstring stretch position (HSP), the knees are maximally extended , whereas in the squatting position (SP), both the hips and knees are maximally flexed .Similar success rates have been reported in studies comparing TSP with modified sitting positions for epidural or spinal anesthesia.