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Back| Local Anesthetic | Concentration (%) | Maximum Single Dose (mg) | Onset Time (min) | Duration of Action (min) | Threshold Dose for CNS Symptoms (mg/kg) |
|---|---|---|---|---|---|
| Tetracaine | 0.2~0.3 | 75~100 | 15~20 | 90~180 | 2.5 |
| Lidocaine | 1.5~2.0 | 400 | 5~15 | 60~120 | 7.0 |
| Bupivacaine | 0.5~0.75 | 150~225 | 10~20 | 120~240 | 2.0 |
| Ropivacaine | 0.5~1.0 | 200 | 10~20 | 120~240 | 3.5 |
Explanation
After puncture and catheterization, the patient is turned to the supine position, and a test dose of 3~5 ml is injected to exclude the possibility of entering the subarachnoid space.
If the patient has no loss of pain sensation in the lower limbs, normal movement, and blood pressure after 5~10 minutes, an additional dose can be injected. The sum of the test dose and the additional dose is called the induction dose, which should not exceed the maximum limit for each local anesthetic. When the effect of the induction dose is about to disappear, 1/3~1/2 of the induction dose is injected to maintain anesthesia.
