Fade Upon TOF Stimulation Induced by Succinylcholine

Study Summary

Muscle relaxants are medications used during surgery to facilitate surgical access. The effect of the muscle relaxant medications is measured by stimulation a motor nerve and measuring the force of the resultant muscle contraction. Based on the mechanism of action, two kinds of muscle relaxants are described. First a nondepolarizing muscle relaxant and the second kind is the depolarizing muscle relaxant. These two kinds of muscle relaxants can be distinguished by rapidly stimulating the nerve 4 times over 2 seconds (Train of four or TOF). The nondepolarizing muscle relaxants produce fade ie successive muscle contractions are less forceful than the preceding ones. Whereas the depolarizing muscle relaxants are generally believed to produce four contractions of equal strength. However, there is some indication that this may not be entirely correct. There is evidence that depolarizing muscle relaxants also may produce fade. The investigators are conducting the following study to determine if indeed depolarizing muscle relaxants produce fade. The investigators would also like to characterize the fade ie differences during onset and offset of the block and the effect of the dose on the degree on the fade.

Primary Outcome

We stimulated the ulnar nerve at the wrist four times (over 1.5 seconds) every 20 seconds. We measured the ratio of the fourth contraction to the first contraction before and after the administration of succinylcholine. Before administering succinylcholine the ratio is normally one. After the administration of succinylcholine the first contraction diminishes, but the fourth contraction diminishes even more. This results in a ratio of T4 to T1 being less than one. The lowest ratio recorded after

Interventions

• DRUG Succinylcholine