The anesthetic effect of lidocaine after varying times of phonophoresis.

OBJECTIVE: This study aimed to determine the anesthetic effect of 1-MHz phonophoresis using lidocaine on the anterior forearm following 5- and 10-min interventions. DESIGN: This was a crossover study in a laboratory involving 22 healthy participants (13 women, 9 men; age, 23.0 ± 3.2 yrs; height, 169.1 ± 7.2 cm; weight, 70.9 ± 13.9 kg). All subjects received four interventions on four different days: (1) 1.5 W/cm, 100% duty cycle with lidocaine for 5 mins (short); (2) 1.5 W/cm, 50% duty cycle with lidocaine for 10 mins (long); (3) no ultrasound for 10 mins with lidocaine gel (lidocaine sham); and (4) no ultrasound for 10 mins with ultrasound gel (true sham). Skin sensation was measured for analysis. The main outcome measures were Semmes-Weinstein Monofilament (SWM) scores, with higher scores indicating less sensitivity. RESULTS: There was a significant time main effect for SWM scores (P < 0.001). Baseline SWM scores were the lowest (3.00 ± .53; P ≤ 0.006) and post-SWM scores (0 mins) were the highest (3.63 ± .44; P < 0.001), indicating an anesthetic effect at this time. CONCLUSIONS: Neither the long nor the short treatment decreased skin sensation compared with sham conditions. All interventions resulted in decreased skin sensation when comparing baseline SWM scores to all posttreatment scores. Phonophoresis with lidocaine did not result in an enhanced anaesthetic effect on human subjects.