Lidocaine for injection can act on the central nervous system and cause symptoms related to the central nervous system, such as drowsiness, abnormal sensation, muscle tremors, convulsions, coma, and respiratory depression, and other very bad adverse reactions. It can also cause slowing of atrial conduction velocity, ventricular conduction block, and suppression of myocardial contractility and decreased cardiac output when the blood oxygen concentration is too high. It should not be used in patients with allergies to lidocaine and other local anesthetic drugs, and is contraindicated in patients with pre-excitation syndrome, severe heart block, and uncontrolled epilepsy. This drug has a high diffusion capacity and is generally not used for subarachnoid block, but only for local infiltration anesthesia. This drug should also be used with caution in patients with hepatic or renal dysfunction, reduced hepatic blood flow, congestive heart failure, severe myocardial damage, and hypovolemic shock.