Apa Quiz2 Flashcards
Single twitch
the first and simplest type of stimulation is a single twitch at 0.1-1 hertz for 0.1-0.2 milliseconds. (ms) These can be delivered automatically every second, every 10 seconds, or manually, depending on the sophistication of the monitor. (Serves as a control twitch)
Train of four
TOF , most widely used means of stimulation is the TOF, which delivers four separate stimuli every 0.5 second at a frequency of 2 HZ for 2 seconds. A comparison is made of the four stimulated responses. Each of the four twitch responses is referred to as T1- T4 respectively. Upon onset of paralysis with a nondepolarizing relaxant, there is a progressive diminution of the twitch response with visible fade. Fade refers to the fact that each successive twitch response is smaller. (see next slide) - When partial paralysis is present yet all four twitch response can be elicited, with fade from T1 through T4 an assessment is made regarding the size of T4 compared to T1. this t4:T1 ratio is referred to as the TOF ratio. When the neuromuscular junction is free of NMBD, all four twitches will be equal. As more receptors are blocked, twitch fade is observed. This is subjective by the anesthetist, and may not be reliable.
Tetanus
consist of continuous electrical stimulation for 5 seconds at 50 or 100 Hz. The 100 Hz is more reliable for detecting fade. If the muscle contraction produced is sustained for the entire 5 seconds of stimulation without fade, significant paralysis is unlikely, If fade is present, clinically significant block remains. The higher the intensity of stimulation produced by tetanic frequencies as compared to TOF, ST, or DBS makes it a useful test when other tests are equivocal. The test is painful and should not be repeated too often to avoid muscle fatigue.
Double burst stimulation
conceptualized as an analog to TOF with some improvements. It consists of two short bursts of a 50Hz tetanus separated by 0.75 seconds. The use of DBS seems to improve the ability to detect residual paralysis during recovery. Fade of the second impulse is comparable to a TOFR of less than 0.6 and indicates significant paralysis.
