Tof-watch nmb monitoring misleading display output during moderate neuromuscular blockade

Abstract

In general anesthesia, Neuromuscular Blockade (NMB) agents are administered to ensure intubation quality and complete immobilization. Monitoring NMB, based on the evoked response evaluation after a peripheral nerve stimulation, is essential to provide insight on medication dosing and suitable approaches for NMB reversal. Professionals often rely on the data displayed on the monitor screen after TOF stimuli, assuming measurements present the expected fade and a TOF-ratio > 90% is enough to rule out residual paralysis. This can be inaccurate and mislead the clinician to extubate before adequate NMB curarization. Data from 31 patients that underwent general anesthesia were retrospectively analyzed. All patients received a standard dose of rocuronium (0.6 mg/kg) for intubation, during maintenance additional rocuronium boluses were administered if solicited. NMB monitoring was done continuously applying TOF stimuli at the adductor pollicis with TOF-Watch SX®. Two types of monitoring display errors were studied: (1) valid TOF value without fade effect (invalid T1 > T2 > T3 > T4); (2) in the 30 min before extubation a valid TOF-ratio value > 90% (without error type 1) with T1 < 70%. Results show a mean (SD) of type 1 error on 42.0 (17.5)% of valid TOF measurements, type 2 error in 63 (45)%. Only 9 patients (29%) presented a TOF with no errors before extubation. These results may increase the distrust in the NMB monitoring devices, however its use should not be rejected when NMB agents are administered. Careful evaluation of the NMB is recommended and additional efforts should be placed in the accuracy of monitors data display to avoid errors.