The authors present a prospective, randomised, triple-blind study to see how long it really takes to obtain the lowest cutaneous haemoglobin concentration after lignocaine with adrenaline injection. Twelve healthy volunteers were injected simultaneously in each arm with either plain 1% lignocaine or 1% lignocaine with 1:100,000 adrenaline, the same person was responsible for performing all injections. Skin and soft tissue perfusion changes were monitored with diffuse reflectance spectroscopy to obtain changes in haemoglobin concentration up to 100 minutes after injection. The lowest mean relative haemoglobin index, indicating the maximal effect of the adrenaline, was at 25 minutes after injection. This is considerably longer than historical quotes of seven to ten minutes.  Further to this, the mean relative haemoglobin values at every time point were significantly different between plain lignocaine and lignocaine plus adrenaline. This demonstrates other novel uses of reflectance spectroscopy to non-invasively monitor tissue perfusion in free flaps. This study is well designed with clear and concise end-points, with strong evidence that can be employed in everyday clinical practice. The authors have also highlighted the possible limitations of skin site, lack of surgical incision to assess bleeding and baseline skin colour. 

Optimal time delay between epinephrine injection and incision to minimise bleeding.
McKee DE, Lalonde DH, Thoma A, et al.
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Neil J Cahoon

St John's Hospital, Livingston, UK.

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