Thermography of the vasodilator effect of local anaesthetics in ingrown toenail surgery

Objectives: Local anaesthetics such as lidocaine or mepivacaine, commonly used in toenail surgery, have an associated vasodilator effect. Although is thought that lidocaine has a greater vasodilator effect than mepivacaine, there´s not strong in vivo evidence of this. So, the aim of this work was to assess the temperature increase experienced by the toes after be injected of 1 ml 2 % mepivacaine or lidocaine. Patients and methods: 26 participants were randomly divided into two groups and a pre-anæsthetic thermal image (Flir E60bx camera) was taken. Patients in group A (n = 13) received 1 ml of 2 % lidocaine, while those in group B (n = 13) received 1 ml of 2 % mepivacaine at four points of the hallux. After 10 minutes a second thermal image (post-anæsthetic image). Mean temperatures were assessed at the proximal phalanx and the pad of the hallux. Results: After application of the anæsthetic, the mean temperatures were 31.3 ± 3.07 °C at point 1 and 30.8 ± 3.08 °C at point 2 in the lidocaine group, and 31.3 ± 2.74 °C at point 1 and 29.5 ± 2.87 °C at point 2 in the mepivacaine group, with not statistically significant differences between them (p = 0.959 and p = 0.798). All the participants experienced temperature increases of between 5.13 °C and 6.91 °C, but there were no significant differences between groups (p = 0.7 and p = 0.0778). Conclusions: Even though most of the literature suggests that lidocaine has more potent vasodilator effect than mepivacaine, the present results do not reflect any real clinical impact distinguishing one drug from the other in the field block of the big toe, as measured with infrared thermal imaging.(AU)