Train of four (TOF)
💥four stimuli {T1-T4} are given at a frequency of 2 Hz (0.5 sec between the stimuli)
💥 Each stimulus in the train causes the muscle to contract and the 'fade' in the response allow us to evaluate the neuro muscular blockade
💥The ratio T4:T1 ( i.e. Dividing the amplitude of the fourth response by the amplitude of the first response ) indicates the degree of neuromuscular block.
💥Non-depolarizing NMBAs produce a decrease in magnitude of the first twitch compared with a pre-relaxant stimulus, and a progressive reduction in magnitude of T1–T4.
💥The number of elicited twitches indicates the degree of receptor occupancy.
💥Disappearance of T4, T3, T2, T1 corresponds to 75%, 80%, 90% and 100% occupancy.
💥With recovery of neuromuscular function the twitches appear in the reverse order.
💥 Accepted values for TOF count are:
🔹 1 twitch for tracheal intubation
🔹1–2 twitches during established anaesthesia
🔹1 twitch for tracheal intubation
🔹1–2 twitches during established anaesthesia
🔹3–4 twitches before reversal of neuromuscular blockade is attempted.
Double burst stimulation
💥 Consists of two bursts ( the duration of each square wave impulse in the burst is 0.2 sec ) at 50 Hz with each triple burst separated by 750 ms.
💥 DBS with 3 impulses in each of the two tetanic bursts is commonly used
💥 These manifest visually as two separate stimuli (T1 and T2).
💥 The ratio is related to the TOF ratio and is easier for the operator to interpret reliably.
💥 Used under light paralysis where train of four ratio is difficult to distinguish
Post-tetanic Count (PTC)
💥 PTC is used when there is no response to TOF stimuli and also when we want to eliminate sudden movements of the patient completely as during ophthalmic and neurosurgery
💥 Uses tetanic stimulation at 50 Hz for 5 s to mobilize presynaptic ACh (to ‘kick start’ the nerve under deep paralysis) .
💥 After a recovery time of 3 sec , it's followed by 20 pulses at 1-2 Hz twitch stimulation
💥 The number of twitches generated (i.e. the post-tetanic count) reflects the degree of neuromuscular blockade.
💥 Shows fade response earlier than train of four
💥 Used under deep paralysis to estimate time to recovery
Reference: frca.uk Anesthesia Monitoring Techniques , Miller's Anesthesia , 7/e
