Priming technique with cisatracurium. Onset time at the laryngeal muscles

Objective. Priming can significantly shorten the onset of nondepolarizing neuromuscular blocking agents (NNBA) measured at the adductor pollicis muscle (APM). In spite of the known risks, priming is very popular especially in cases where NNBAs with a long onset time are used. However, there are no data regarding the onset of action for a priming technique measured at the laryngeal muscles although these muscles are of great importance for conditions of intubation and patient safety. The aim of this study was to compare a bolus application and a priming technique with respect to the laryngeal onset time and peak effect. Patient and methods. After approval of the local ethics committee and written informed consent, 36 patients undergoing elective thyroid surgery were enrolled in the study. Anesthesia was induced and maintained with a target controlled infusion of propofol (target concentration 2.7-6.0 mu g/ml) and infusion of remifentanil (0.25-0.75 mu g/kgbw/min). After loss of consciousness, a tube with a surface electrode was placed into the trachea without the application of any neuromuscular blocking agent. Neuromuscular monitoring consisted of evoked electromyography (EMG) of the laryngeal adductor muscles via the surface electrode and evoked acceleromyography (TOF Guard (R)) of the right adductor pollicis muscle (APM). After transcutaneous stimulation of the recurrent laryngeal nerve and uInar nerve, either 0.9% NaCl followed by 0.1 mg/kgbw cisatracurium after 3 min (bolus group, n=12), a priming dose of 0.01 mg/kgbw cisatracurium followed by 0.09 mg/kgbw 3 min later (low dose priming group, n=12) or a priming dose of 0.015 mg/kgbw cisatracurium followed by cisatracurium 0.085 mg/kgbw 3 min later (high dose priming group, n=1 2) were injected. Lag time, onset time and peak effect of NMB were recorded and compared between the groups. Results. Demographic data, lag time and peak effect were comparable between the three groups. Onset time at the laryngeal muscles was significantly shorter in the high dose priming group (80 +/- 17 s), when compared to the low dose priming group (128 +/- 23 s) and bolus group (142 +/- 29 s). Onset time at the APM was also significantly shorter in the high dose priming group (154 +/- 35 s), when compared with the bolus group (226 +/- 76 s). The recovery of the neuromuscular function measured at the APM showed no differences between the groups. Conclusion. Our results show that only high dose priming of cisatracurium can significantly shorten the laryngeal onset time. However, clinical routine use is not recommended due to possible side-effects.