Does monitoring of post-tetanic count prevent alarms of airway pressure or visible muscle activity during intratracheal jet ventilation? A prospective study with five different neuromuscular blocking agents.

Objective: Profound neuromuscular block (NMB) quantified by post-tetanic count (PTC) may prevent all muscle activity during anesthesia. We studied whether monitoring of PTC prevents airway pressure alarms or visible movements of the vocal cords and the abdomen during endolaryngeal procedures (ELPs).

Methods: In this prospective, double blind, study 50 healthy (ASA 1-3) patients scheduled for ELPs were randomized into five groups: atracurium, mivacurium, rocuronium, vecuronium and succinylcholine. During alfentanil-propofol anaesthesia, profound NMB was controlled by monitoring the PTC (target level PTC 0-2, 50 Hz tetanic stimulation) of the adductor pollicis muscle. The muscle relaxants were administered using bolus dosing in all groups but in the succinylcholine group. The early signs of recovery of NMB to be observed were: 1) airway pressure alarms, 2) movements of vocal cords on the laryngeal video monitor and 3) movements of the abdomen. The inference was based on 90% confidence interval tests.

Results: During 50 ELP:s following signs of early recovery of NMB were recognized: 2 alarms of airway pressure, 16 laryngeal movements and 11 movements of the abdomen. The proportion of airway pressure alarms was significantly lower than proportion of all detectable movements (95% confidence interval analysis). Twelve of the movements were recorded at PTC zero level. The signs of early recovery of NMB were detected in all groups.

Conclusions: PTC-monitoring following 50 Hz stimulation does not ensure total inactivity of muscles during alfentanil-propofol anesthesia, regardless which relaxant has been chosen. During ELPs, simultaneous observation of the vocal cords and the abdomen is more sensitive in detecting early recovery of NMB compared to our method of airway pressure monitoring.