At present, the most common application of spinal anesthesia is lumbar epidural combined anesthesia or single lumbar anesthesia. Every detail of puncture and administration will affect the quality of anesthesia, and the selection of intervertebral space for puncture is theoretically related to neurological complications. Therefore, in order to achieve satisfactory anesthesia results, it is necessary to start with positioning and puncture.
In modern anesthesiology, when performing lumbar anesthesia puncture, L2-3 or L3-4 spinous process spaces can be selected. However, many colleagues still recommend using the L3-4 spinous process gap and abandoning the L2-3 gap when discussing the implementation and complications of spinal anesthesia. The reason is simple: there are still a small number of adults with spinal cord terminals that exceed the L2 gap. Choosing L3-4 can avoid accidental injury to the spinal cord by puncture.
According to magnetic resonance imaging examination statistics, the end of the spinal cord cone is approximately 1.19% located in the L2-3 gap or the upper end of the L3 vertebral body. However, in daily puncture positions, when the head is in a low flexion position, the end of the spinal cord will move up about 1.5cm to the head side. In addition, the end of the spinal cord is suspended in the cerebrospinal fluid, and the puncture diameter does not deviate. When breaking through the dura mater, the possibility of accidental injury to the spinal cord nerves is not significantly different between L3-4 and L2-3. Miller's Anesthesiology Eighth Edition pointed out that there is no difference in the risk of puncture between the two in large sample statistics.
The incidence of nerve injury in all spinal canal punctures is 3.5-8.3/10000 for lumbar anesthesia and 0.4-3.6/10000 for epidural anesthesia, according to data. Careful analysis of nerve injury data in spinal anesthesia reveals that there are not many reports of direct damage to the spinal cord. Most of the causes reported are incorrect positioning, anatomical abnormalities in the spinal canal itself, and rough puncture techniques. Adequate preoperative preparation and attention to surgical techniques are more important than choosing L3-4 rather than L2-3 for the puncture site.
The most common and important nerve damage in clinical practice is actually the damage to the spinal nerve roots that should be paid more attention to. The ganglia of the spinal nerve root and dorsal root are the main sites of spinal anesthesia, and the spinal nerve root is also a common vulnerable area. One is that the position of the spinal nerve root is fixed, and during puncture, it deviates from the midline. The most easily touched part is the spinal nerve root. Slowly insert the needle during puncture, and adjust it promptly if there is any discomfort, which can avoid damaging the spinal nerve root.
The second vulnerable area of the nerve is the cauda equina. Although there are not many reports of direct puncture injury to the cauda equina, physical damage is rare, and chemical damage caused by anesthetic drugs should be given more attention. The occurrence of TNS in spinal anesthesia is related to the type of spinal anesthesia drug, but the incidence rate is not linearly proportional to the concentration and dosage of the injected drug. The important reason is that spinal anesthesia drugs are injected into cerebrospinal fluid and then spread with it. The dilution effect of cerebrospinal fluid protects and weakens the toxicity and degree of damage of spinal anesthesia drugs.
During spinal anesthesia, the cauda equina nerve is hidden in the sacral curvature and is thin without sheath protection. For example, in L3-4 puncture, the anesthetic is used with a heavy density and slowly pushed towards the tail. After puncture, the patient quickly places the lithotomy position, which can exacerbate the curvature of the sacral curvature. If the overlapping factors affect the flow of cerebrospinal fluid, it can cause the accumulation and poor diffusion of spinal anesthesia drugs in the sacral curvature. At this time, the toxicity of local anesthesia drugs will be significantly enhanced, which can cause TNS or more serious cauda equina syndrome in the cauda equina nerve. The probability of this occurrence is still high. If the recovery of movement and sensation in the perineum, legs, and ankles is strictly evaluated 24 hours after surgery, as well as the recovery of urination sensation, the safety is very high. Ropivacaine spinal anesthesia can cause reflex and sensation of movement, urination, and defecation. If not fully recovered, the incidence can exceed 40%. Two to three days after a spinal anesthesia cesarean section, more than half of the patients still experience abnormal sensations during urination, discomfort such as abnormal sensations in the perineum and difficulty urinating. Most of these symptoms gradually disappear within about a week, and there are still a few cases that take more than a month to fully recover. It should be noted that if the above-mentioned factors of spinal anesthesia drug aggregation are combined with other factors, such as the injection site is inclined to the corner of the subarachnoid space, the patient's spinal canal is narrow, and diabetes is complicated, etc. The degree of nerve damage may worsen. At this time, lumbar puncture L3-4 is more prone to cauda equina nerve damage than L2-3.
The closer the ratio of spinal anesthesia drugs is to the physical and chemical properties of cerebrospinal fluid, the safer it is. When diluting spinal anesthesia drugs with cerebrospinal fluid or similar physiological saline, 5% glucose can be used instead of higher concentrations when selecting heavy density drugs. High capacity and low concentration spinal anesthesia drugs should be used as much as possible. When the volume of the medication is large, diffusion is easier to distribute evenly. When injecting spinal anesthesia drugs, do not be too slow. You can also use the wheel injection method to inject the drugs, or after injecting the spinal epidural combined with spinal anesthesia drugs, inject a certain amount of saline or spinal epidural anesthesia drugs into the hard outer cavity, which can help the diffusion of spinal anesthesia drugs. After injecting spinal anesthesia medication, wait for at least five minutes before placing the lithotomy position. Both may reduce the chances of poor drug diffusion and corresponding nerve damage. The occurrence of nerve damage caused by spinal anesthesia should be comprehensively considered, not only by evaluating the preoperative patient's physical condition, the anatomical condition of the puncture site, the details of the puncture operation, drug ratio and injection, but also by considering the influencing factors during surgery. Strictly controlling all aspects of spinal anesthesia and comprehensively treating them can better prevent and reduce corresponding complications.