MONITORING OF NEUROMUSCULAR BLOCK : DO YOU FREQUENTLY FORGET THE NUMBERS RELATED TO TOF, DBS & PTC?

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