Onset of Action for Lignocaine (Lidocaine)
Lignocaine has an almost immediate onset of action when administered intrapleurally, and should therefore be given just before the sclerosant during pleurodesis procedures 1. However, the onset time varies significantly depending on the route and method of administration.
Route-Specific Onset Times
Topical/Mucosal Application
- 3-5 minutes for topical anesthesia on mucous membranes 2
- 2-5 minutes when used with epinephrine for topical anesthesia 3
- Ineffective when applied to intact skin 2
Infiltrative/Injection Anesthesia
- Approximately 1 minute for standard infiltrative anesthesia 3
- 1.3 minutes (range 1-2.7 minutes) for digital nerve blocks 4
- 11.2 ± 5.1 minutes for intravenous regional anesthesia (IVRA), with satisfactory surgical conditions achieved within 20 minutes 5
Intraoral Nerve Blocks
- 3-5 minutes for standard lignocaine injection 6
- 34.4 seconds (mean) when alkalinized with sodium bicarbonate, compared to 109.8 seconds without alkalinization 6
Factors Affecting Onset Time
Alkalinization Significantly Accelerates Onset
- Adding 8.4% sodium bicarbonate in a 1:10 dilution reduces onset time by approximately 70% for intraoral blocks 6
- Buffering with sodium bicarbonate decreases injection pain while maintaining effectiveness 7, 3
Addition of Epinephrine
- Epinephrine extends duration (90-200 minutes) but does not significantly delay onset 3
- Provides faster onset and longer duration compared to lignocaine alone 3
Concentration and Site
- Higher concentrations and specific anatomical sites affect absorption rate 2
- Intratracheal administration results in the most rapid absorption 2
Clinical Implications for Timing
For intrapleural administration during pleurodesis, lignocaine must be given immediately before the sclerosant because its onset is almost instantaneous 1. The British Thoracic Society guidelines specifically recommend administering lignocaine (3 mg/kg; maximum 250 mg) intrapleurally just prior to sclerosant administration 1.
Important Safety Considerations
- Wait at least 4 hours between lignocaine administration and other local anesthetic interventions to prevent cumulative toxicity 1, 7, 8
- No nerve or fascial plane blocks should be performed until 4 hours after completion of an intravenous lignocaine infusion 1
- Monitor for early signs of toxicity including circumoral numbness, facial tingling, and slurred speech 7, 3
Comparison with Other Local Anesthetics
Lignocaine is classified as having rapid onset compared to other local anesthetics 9: