The sacral cavity is a continuation of the epidural space in the spine, with its upper end located at the junction of 1-2 sacrum and its lower end ending at the sacral fissure. The lumen is rich in vascular plexus, lymphatic vessels and loose connective tissue. The volume of normal adult sacral cavity is about 25ml. Since the sacral cavity is farther away and the epidural cavity in other parts is wide, the distance from the sacral fissure to the terminal of subarachnoid space is farther (19-75mm, average 47mm), with a 50 mm long puncture needle, generally there is no danger of accidentally entering the subarachnoid space and causing total spinal anesthesia, so it is safer and very suitable for general surgery in the anus, and it is more often used clinically. It is very suitable for general anal surgery and is more commonly used in clinical practice. How to anesthetize mixed hemorrhoids? The patient is placed in a lateral position with the back arched backwards and the knees drawn close to the abdominal wall. After routine disinfection of the perineum, anus and sacrococcygeal area, a sterile towel is laid. The tip of the coccyx is first felt, and the two sacral angles can be felt about 4-125px upward, and a bony elevation can be felt as the fourth middle sacral spine in the middle part further upward. Between the two sacral horns and the fourth middle sacral spine is a soft tissue depression, namely the sacral fissure, and the bony edge can be felt at the depth. With a 20 ml syringe, the drug is inhaled and a 6 or 61/2 gauge needle is attached. A mound is first injected at the sacral fissure, then the needle is advanced in a perpendicular direction to the skin, and a small amount of anesthetic is injected as the needle is advanced to infiltrate the deeper tissues and sacrococcygeal ligament. Continue to enter the needle, when the needle tip penetrates the sacral fissure, the sacrococcygeal ligament and other fibrous connective tissue, the resistance abruptly decreases and there is an obvious feeling of falling, indicating that the needle tip has entered the sacral canal lumen. Re-enter the needle a little and draw back the syringe, if there is no blood and cerebrospinal fluid, it means that the needle tip has not entered the blood vessel or subarachnoid cavity by mistake, at this time, 20-30ml of medicine can be injected, during the injection process, it should be drawn back twice, and if there is no blood and cerebrospinal fluid, continue to inject medicine. Because the injected drugs are different, so their effects, latency period and anesthesia maintenance time are also different. Commonly used local anesthetic drugs are: 1, 1% lidocaine and 2% procaine equivalent mixture; 2, 2% lidocaine and 0.5% bupivacaine equivalent mixture, etc.