Anesthesia; Adverse Effect, Spinal and Epidural

The objective here is to quantify the number of punctures and redirections during routine practice in the anesthesiology department, verify the final angle of incidence and the sac-skin distance by ultrasound, and determine the optimal, maximum, and minimum angles that would have allowed successful punctures. The objective is also to correlate ultrasound and plain X-ray distances, if available. These angles would then be inferred in advance in patients who must undergo spinal anesthesia, assessing whether this prior estimate reduces the number of punctures and redirections.