Use of adrenaline in digital nerve blocks

To the Editor: Adrenaline is often added to local anaesthetic for injection because the vasoconstrictive effect of the catecholamine counteracts the dilative effect of the local anaesthetic, decreasing systemic absorption and prolonging its action.1 Traditionally, the use of this drug combination has been discouraged in structures supplied by end arteries — most notably the digits, but also the nose, ears and penis — on the basis that it may precipitate irreversible arterial vasospasm, leading to tissue necrosis.

In a review of the literature on digital infarction from 1927 to September 2011, including comprehensive reviews2 and prospective trials,3 21 cases of digital infarction were identified that were associated with the use of adrenaline (usually with procaine or novocaine) and 27 where adrenaline was not used.2 In each affected patient, additional factors such as tight tourniquets, antiseptic burns, procaine degradation products, peripheral vascular disease and large volumes of injection were considered to be contributing factors. No reported cases of digital ischaemia are attributable to adrenaline alone.

A 20-patient randomised controlled trial showed no statistically significant decrease in fingertip capillary partial pressure of arterial oxygen (PaO2) and arterial oxygen saturation (SaO2) after 15 minutes when adrenaline was added to lignocaine for digital ring blocks.4 Further, 1111 patients have been described in case series and retrospective reviews where adrenaline has been incorporated to no ill effect.5

These findings suggest that there is no strong evidence supporting the traditional avoidance of adrenaline in these clinical situations. Its use has been shown to have benefit for the patient by removing the need for a tourniquet and sedation or general anaesthesia.5

Undoubtedly, adrenaline causes decreased arterial flow and vasoconstriction, and there is potential for complications in patients with additional factors that may lead to impaired circulation. The use of adrenaline in digital blocks appears to be safe and advantageous for many patients and may be of particular value in general practice, but caution should be exercised when it is used in patients with pre-existing impaired digital circulation.