What is the maximum dose of lignocaine which can be given with adrenaline for ocular blocks?
**Core Concept**
Lignocaine with adrenaline is commonly used for ocular blocks due to its vasoconstrictive properties, which reduce bleeding and prolong the duration of the block. However, the maximum dose of lignocaine is crucial to avoid systemic toxicity.
**Why the Correct Answer is Right**
The maximum dose of lignocaine with adrenaline is 7 mg/kg. This is because adrenaline (epinephrine) has a synergistic effect with lignocaine, increasing its toxicity threshold. The combination of lignocaine and adrenaline is used for ocular blocks, and the maximum dose is critical to prevent systemic toxicity, which can manifest as CNS excitement, seizures, or cardiac arrhythmias. The mechanism of action of lignocaine is through the inhibition of sodium channels, leading to neuronal blockade.
**Why Each Wrong Option is Incorrect**
**Option A:** 5 mg/kg - This is below the recommended maximum dose for lignocaine with adrenaline, which may not provide adequate anesthesia for ocular blocks.
**Option B:** 10 mg/kg - This is above the recommended maximum dose, increasing the risk of systemic toxicity.
**Option C:** 4 mg/kg - This is also below the recommended maximum dose, which may not provide adequate anesthesia for ocular blocks.
**Clinical Pearl / High-Yield Fact**
When using lignocaine with adrenaline for ocular blocks, always calculate the maximum dose based on the patient's weight and ensure that the total dose does not exceed 7 mg/kg to avoid systemic toxicity.
**Correct Answer: D. 7 mg/kg**