Write a short note on Adrenaline with Local Anaesthetics.

Rationale

Adrenaline is added to local anaesthetic solutions as a vasoconstrictor. By constricting local blood vessels it slows the systemic absorption of the LA, which produces several benefits: it prolongs and intensifies the block, reduces the peak plasma concentration (raising the maximum safe dose), and reduces bleeding in the surgical field.

Contraindications & Cautions

Adrenaline-containing solutions must not be used in areas supplied by end-arteries — fingers, toes, penis, nose and ears — because vasoconstriction can cause ischaemic necrosis. They are used cautiously in ischaemic heart disease, severe hypertension, arrhythmias and hyperthyroidism (systemic adrenaline effects), and it adds little to bupivacaine.

The ‘fingers and Toes’ Rule

The classical teaching that adrenaline must never be used in ‘fingers, toes, penis, nose and ears’ captures the principle that tissues supplied by end-arteries, without a collateral blood supply, are vulnerable to ischaemic necrosis if their single arterial inflow is constricted. Although some modern evidence suggests carefully-prepared low-concentration adrenaline solutions may be safer in the digits than once thought, the safe and examinable rule remains to use plain local anaesthetic in these areas, reserving adrenaline for sites with a rich collateral circulation.

Contraindicated in end-artery territories.

• Adrenaline vasoconstricts → slows LA absorption → longer/denser block, higher safe dose, less bleeding.
• Contraindicated in end-artery areas: fingers, toes, penis, nose, ears (necrosis).
• Caution in IHD, hypertension, arrhythmias, hyperthyroidism; little benefit with bupivacaine.
• Raises lignocaine max dose from 3 to 7 mg/kg.