Frenular Injury During Insertion of the ProSeal Laryngeal Mask Airway Using the Introducer Tool Technique

could decrease the difference in excitability between nerve and muscle (1). However, we think that an increase in stimulus duration from 0.2 to 0.3 ms is unlikely to affect the likelihood of direct muscle stimulation. Dr. Kopman did not accurately reproduce Mortimer’s (2) Figure. The figure should have been drawn with a logarithmic x-axis. As shown in the redrawn figure (Fig. 1), the 0.2-ms and 0.3-ms durations are both in the range where the excitability gap between nerve and muscle is wide. The chronaxie is at least 10 times less in nerve (1 ms) than in muscle ( 10 ms). There are few data in the peer-reviewed literature about strengthduration curves in paralyzed muscle. In 1974, paralyzed muscle of cats was stimulated at supramaximal current for nerve stimulation. The resulting contraction was 3.5%–7% of that obtained in non paralyzed muscle; the smaller number was obtained with shorter duration stimulation (3). These data were obtained with needle electrodes, and the use of surface electrodes might produce different results. Recently, the differential response to short and long pulses was used in the diagnosis of denervation, as denervated muscle responds only to long (1 ms to 20 ms) pulses (4). However, the difference in excitability between nerve and muscle is not infinite, and direct muscle stimulation may occur in practice with stimulation at the wrist or at the hand. In our study, (5) we had evidence of direct muscle stimulation with stimulation at the wrist in two patients. In practice, such an occurrence can be detected by 1) absence of fade, 2) small amplitude of the twitch, and 3) disappearance of the response when the location of stimulating electrodes is changed (Fig. 2).