After local anesthetics are injected into the subarachnoid space, it takes some time to fully exert their blocking effect on the nerve roots. This period is called the spinal anesthesia induction time. The length of the induction time is related to the type of drug, the specific gravity of the solution, and the method of preparation. The duration of spinal anesthesia is related to the type and dose of the drug, mainly depending on the concentration of the drug, which is positively correlated. However, excessively high concentrations can damage nerves and cause permanent paralysis, so the appropriate concentrations of different drugs for subarachnoid block are limited in clinical practice.