Background: Skin wrinkling on water immersion is a reliable and simple test of sympathetic innervation. The eutectic mixture of local anesthetic (EMLA) cream has been shown to induce near identical clinical wrinkling scores and reduction in digit blood flow as that following water immersion in people with normal sympathetic innervation. This study was designed to investigate the vasomotor response to EMLA in replanted fingers that had poor sympathetic innervation.
Methods: Laser Doppler imaging (PeriScan PIM II; Perimed AB, Stockholm, Sweden) was used to detect perfusion changes in the pulps of fourteen replanted fingers before and after 0.5 g of 5% EMLA cream application and water immersion in a 40 degrees C normal saline for 30 min, respectively. Comparisons were made with the contralateral corresponding normal fingers.
Results: After water immersion and EMLA application, all of the normal fingers showed a considerable and similar decrease in blood perfusion that demonstrated in the absolute perfusion units (pU) (baseline: 1.57 +/- 0.33 pU, after water-immersion, 1.19 +/- 0.22 pU, P < 0.001; decrease: 23.6 +/- 7.7%, after EMLA application: 1.20 +/- 0.18 pU, P < 0.001; decrease: 22.4 +/- 8.9%). In contrast, all of the replanted fingers showed a statistically significant vasodilatatory response (baseline: 1.20 +/- 0.29 pU, after water-immersion: 1.36 +/- 0.28 pU, P < 0.001; increase: 15.2 +/- 9.1%, after EMLA application: 1.38 +/- 0.27 pU, P < 0.001; increase: 16.8 +/- 9.1%).
Conclusions: EMLA and water immersion both cause vasodilatation and no skin wrinkling in replanted fingers. These results imply that intact sympathetic nerve function is required to induce the vasoconstrictive effect of EMLA.