Question
The maximum safe dose for Lignocaine (without adrenaline) as a local anaesthetic drug is:
| A. |
3 mg/kg
|
| B. |
5 mg/kg
|
| C. |
7 mg/kg
|
| D. |
9 mg/kg
|
Show Answer
|
Correct Answer » B
Explanation
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|
Lignocaine (Lidocaine)
Classification
Mechanism of Action
- Reversibly blocks voltage-gated sodium (Na⁺) channels
- Prevents initiation and propagation of nerve impulses
Uses
- Local infiltration anesthesia
- Peripheral nerve block
- Epidural anesthesia
- Spinal anesthesia (5% hyperbaric solution)
- Intravenous antiarrhythmic (Class IB)
Maximum Safe Dose
- Without adrenaline: 4.5–5 mg/kg (maximum 300 mg)
- With adrenaline: 7 mg/kg (maximum 500 mg)
Signs of Systemic Toxicity
- Circumoral numbness (earliest sign)
- Tinnitus
- Metallic taste
- Dizziness
- Seizures
- Hypotension
- Cardiac arrhythmias
- Cardiac arrest
Why Adrenaline is Added
- Prolongs duration of action
- Reduces systemic absorption
- Decreases toxicity
- Provides a relatively bloodless surgical field
Contraindications to Lignocaine with Adrenaline
- End-artery areas (fingers, toes, nose, pinna, penis)
- Severe peripheral vascular disease
- Intravenous regional anesthesia (Bier’s block)
