A C Young-Ho Kim, et al. B D responses. Above 1 MAC, no contralateral responses were elicited (p < 0.010) (Fig. 1D). When the percent of contrala- teral responses obtained below 1 MAC was compared to those obtained above 1 MAC, the differences were statisti- cally significant (p < 0.010) (Table 1). Protocol 2 Results of Protocol 2 are shown in Table 2. Again, as with the results of Protocol 1, the number of contralateral response underwent marked declination with anesthesia levels above 0.75 MAC. No contralateral response could be elicited with anesthesia levels at or above 1 MAC. When the percent of contralateral responses obtained below 1 MAC was com- pared to those obtained above 1 MAC, the differences were again statistically significant (p < 0.010) (Table 2). In one subject, R2 responses with the average latency of 84 msec (range 55.5-136 msec) were recorded at 0.5 MAC anesthesia level (Fig. 2). Fig. 1. Stimulation of the left internal branch of SLN. Compound muscle action potential (CMAP) recordings obtained from ipsilateral thyroarytenoid muscle at (A) 0.5 MAC, and (B) 1 MAC, from contralateral thyroarytenoid muscle at (C) 0.5 MAC, and (D) 1 MAC. DISCUSSION As in our previous study with pig model, the canine model Table 1. Left iSLN Stimulation MAC; minimal alveolar concentration. Latency: average ± 1 SD. *p < 0.010 (Student’s t-test). Table 2. Right iSLN Stimulation Ipsilateral R1 Efficiency (%) Latency (ms) Contralateral R1 Efficiency (%) Latency (ms) Ipsilateral R1 Efficiency (%) Latency (ms) Contralateral R1 Efficiency (%) Latency (ms) MAC; minimal alveolar concentration. Latency: average ± 1 SD. *p < 0.010 (Student’s t-test). < 0.5 30 / 30 (100) 26.7 ± 1.2 20 / 30 (67) 27.3 ± 0.7 < 0.5 19 / 19 (100) 21.4 ± 2.6 24 / 27 (89) 22.3 ± 2.3 0.5 MAC 0.75 1.0 > 1.0 5 / 5 (100) 52 / 52 (100) 26.2 ± 1.5 17 / 17 (100) 34 / 34 (100) 31 / 33 (94) 65 / 67 (97) 26.7 ± 1.4 24.7 ± 3.4 27.4 ± 0.9 11 / 15 (73) 36 / 65 (55)* 29.4 ± 1.0 5 / 20 (25) 28.8 ± 0.7 1 / 17 (6) 0 / 23 (0) 1 / 40 (2.5)* 28.0 ± 0.0 MAC 0.75 0.5 1.0 > 1.0 6 / 6 (100) 40 / 40 (100) 21.6 ± 0.4 15 / 15 (100) 33 / 33 (100) 32 / 34 (94) 65 / 67 (97) 21.8 ± 1.4 22.6 ± 2.4 26.1 ± 1.6 19 / 21 (90) 46 / 74 (62)* 23.8 ± 0.8 13 / 26 (50) 24.0 ± 1.6 1 / 15 (7) 0 / 16 (0) 1 / 31 (3.2)* 26.5 ± 0.0 382 Yonsei Med J http://www.eymj.org Volume 50 Number 3 June 2009