Spinal anesthesia is the abbreviation of subarachnoid anesthesia, that is, local anesthetic is injected into subarachnoid space through lumbar intervertebral space to block nerve roots in this area. (a) the puncture step is often taken in the lateral position, with the back flush with the edge of the operating table, knees bent with both hands, and the spine bent as much as possible to widen the spinous process of the lumbar spine. In order to avoid damaging the spinal cord, the puncture point should be selected in the 3-4 or 4-5 space of the lumbar spine (Figure 1-28). The connecting line of bilateral iliac crest passes through the spinous process of the fourth lumbar vertebra or the 3-4 space of lumbar vertebra, which is used as the positioning standard. Disinfect the skin, cover it with a sterile towel, use 0.5- 1% procaine as infiltration anesthesia at the puncture point, and select a thin lumbar puncture needle (22-26g). In the middle puncture, the lumbar puncture needle should puncture in the direction parallel to the spinous process, and the needle tip will enter the epidural space through the skin, subcutaneous, supraspinous ligament, interspinous ligament and ligamentum flavum, and then push forward to puncture the dura mater and arachnoid membrane. There is often a clear sense of breakthrough when crossing the ligamentum flavum and dura mater. When cerebrospinal fluid flows out of the needle core, local anesthetic can be injected (Figure 1-29). There are the following kinds of commonly used local anesthetics, and solutions with high specific gravity are generally used (table 1- 13). Such as: ① 6% procaine sugar solution (procaine powder 150mg+0. 1% epinephrine 0.2ml+5% glucose 2.3ml). ② mixture of1%tetracaine, 10% glucose and 3% ephedrine, each 1 ml. ③ 0.75% bupivacaine (containing sugar). (II) Physiological changes Cerebrospinal fluid is colorless and transparent, with a pH of 7.40 and a specific gravity of 1.003 ~ 1.008. Local anesthetics diffuse through cerebrospinal fluid and directly act on spinal nerve roots entering part of spinal cord. Anterior root anesthesia can block motor nerves (muscle relaxation) and sympathetic efferent fibers (vasodilation, bradycardia, etc. ); After posterior root anesthesia, sensory nerve (sensory disappearance) and sympathetic afferent fibers can be blocked. The thickness of various nerve fibers varies. The larger the diameter, the higher the drug concentration and the longer the induction time. When local anesthetics spread to the head in cerebrospinal fluid, the smallest sympathetic nerve fiber was blocked first, followed by sensory nerve, and the thickest motor nerve fiber was finally blocked. After sympathetic nerve block, the resistance blood vessels and volume blood vessels in the dominant area are expanded, the volume of vascular bed is rapidly expanded, and the effective circulating blood volume is relatively insufficient. According to the degree of anesthesia, blood pressure has decreased in different degrees, and the extent of the decrease depends on the range of block, which can be compensated by vasoconstriction in the anesthesia area. High block is more likely to cause hypotension. Most parasympathetic nerve fibers are not blocked except sacral segment, so there are bradycardia, intestinal contraction and peristalsis, nausea and vomiting caused by pulling internal organs. After the sensory nerve fibers are blocked, the pain in the same area disappears. After the motor nerve fiber is blocked, the skeletal muscle dominated by it relaxes. Diaphragm is innervated by cervical nerve 3 ~ 4, and intercostal muscle is innervated by thoracic nerve 1 ~ 2. When the diaphragm and intercostal muscle are completely paralyzed, spontaneous breathing disappears, but only when intercostal muscle is completely paralyzed, respiratory depression occurs. 1. Blood pressure drop mostly occurs in patients with high degree of anesthesia, insufficient preoperative preparation or poor general condition. After anesthesia begins, venous access should be maintained and blood volume should be appropriately expanded. Mild blood pressure drop, intramuscular injection of ephedrine 30mg (adult), rapid intravenous drip 15mg, serious cases of accelerated infusion. For blood pressure drop and bradycardia caused by visceral traction, surgical stimulation should be suspended, atropine 0.5mg should be injected intravenously, and vasoconstrictor should be used if necessary. 2. Respiratory inhibition after thoracic spinal nerve block, intercostal muscle paralysis, the body relies on diaphragm compensation. At this time, patients can be encouraged to take a deep breath, take oxygen or help breathing to keep adequate lung ventilation. If the diaphragm is paralyzed and breathing stops, artificial respiration should be given immediately for first aid. At the same time, we should pay attention to circulation and corresponding treatment. 3. headache after lumbar puncture, cerebrospinal fluid constantly leaks into epidural space from puncture hole, causing intracranial pressure to drop and intracranial blood vessels to dilate, thus causing vascular headache. Most of them occur in 1 ~ 3 days after anesthesia, which is aggravated when looking up or sitting up, and relieved or disappeared after lying down. In order to prevent headache after spinal anesthesia, 26G thin waist needle should be used to avoid repeated puncture, and fluid replacement should be paid attention to during and after operation to prevent dehydration. The main measures after headache are bed rest, intravenous infusion and symptomatic treatment. When necessary, the epidural space is filled with normal saline (or dextran). 4. Urinary retention is mainly due to the late recovery of bladder function after sacral nerve anesthesia, which is more common after anal or perineal surgery. Premature bladder filling caused by rapid infusion during operation or postoperative wound pain can affect urination. After urinary retention occurs, it should be treated by hot compress, physical therapy, acupuncture and catheterization. Conclusion: For patients with intraoperative hypotension under subarachnoid anesthesia, vasopressor is faster than rapid fluid replacement, with satisfactory effect, which is worthy of clinical promotion.