[AmadKamali]

The reasons are related to anatomy of spinal column. In adults the spinal cord ends at lower level of second lumbar vertebra. The sheaths/coverings of spinal cord extend all the way down to cocyx. This creates a hollow tube filled only with cerebrospinal fluid from second lumbar vertebra down to end of spinal column. Most of the epidural anesthesia techniques and all of spinal anesthesia techniques use this space because there is no risk of damage to spinal cord. In epidural anesthesia, the catheter can only be advanced a few vertebra up and down from point of insertion. The regions on which surgery can be performed depend on reach of epidural catheter. So, with an epidural catheter in lumbar region, only lower limbs and lower abdomen can be anesthetized. With epidural cathetr in lower thoracic vertebra , approx. lower 2/3 of abdomen can be anesthetized. For chest surgeries you will need epidural catheter in mid thoracic vertebras. And so on. But the problem with thoracic epidural is risk of puncture of dural sheath and damage to spinal cord which will result in permanent paralysis of that area. Epidural anesthesia can be used for upper abdominal and chest surgeries but the risk will be more. Moreover, for extensive surgeries a lot more is needed just simple loss of sensation. for example, more granular control of heart rate, blood pressure, oxygenation etc ; all these manoeuvres are a lot easier in general anesthesia. So for lower limbs to lower abdomen , spinal and epidural anesthesia are fine, even better compared to general anesthesia (especially in obstetrics). For the rest, depends on specific circumstances.