Train of four responses in paretic limbs

Quadriplegic patients pose difficulty for neuromuscular monitoring owing to nonavailability of accessible normal muscle. It is known that train of four responses (T4/T1 ratio) was exaggerated in paretic limbs. However, no studies have quantified the exaggeration at different degrees of block. This study was undertaken to quantify the exaggeration of train of four responses in paretic limbs with increasing levels of block after the administration of neuromuscular blocking drugs. Nine patients with normal motor power (group N) and 9 patients with paraplegia (group P) were studied. The mean difference in T4/T1 ratio (95% CI) between upper limb and lower limbs in normal group at T4/T1 81-90, T4/T1 71-80, T4/T1 51-70, T4/T1 31-50, and T4/T1 0-30 were 8.9 (0.8 to 16.9), 11.6 (3.8 to 19.5), 5.1 (-8.6 to 18.8), 7.6 (-6.8 to 21.9), and 3.8 (-0.9 to 8.5) and in paraplegic group, 14.5 (7.6 to 21.5), 25.1 (13.9 to 36.4), 35.6 (27.5 to 43.7), 29.1 (15.4 to 42.7), and 60 (39.4 to 80.7), respectively. There was a statistically significant difference in the train of four responses between normal and paretic limbs at all levels of block except at T4/T1 81-90. There was a significant positive correlation between difference in the T4/T1 ratio between the upper and lower limbs and intensity of block in the paraplegic group but no correlation in the normal group. The observation that T4/T1 ratio enhancement in denervated limbs is dependent on depth of neuromuscular block may have future implications for monitoring and reversal of neuromuscular block in this patient population.