mivacurium and Thyroid-Diseases

Recurrent laryngeal nerve palsy is a serious complication of endocrine surgery to the neck. Permanent lesions are still occurring in about one in a hundred, despite standardized surgical approach to the nerve and the availability of recurrent laryngeal nerve monitoring. Intraoperative recurrent laryngeal nerve monitoring is based on the visual or acoustic registration of evoked electromyography of the laryngeal muscles. Primarily, it proves conductivity of the stimulated nerve segment towards the muscle, so that stimulation distal of the lesion should show persistent electromyographic response.. In a porcine model, an iatrogenic nerve lesion of the recurrent laryngeal nerve was set. Subsequently, the proximal and distal dissected nerve portion was stimulated and the evoked electromyographic response of the laryngeal muscles was recorded by needle and laryngeal surface electrodes.. As expected, no signal was obtained from the proximal segment. Meanwhile, the distal segment showed unchanged amplitude of the electrophysiological response for the observation period of more than 1 h.. This result demonstrated a remarkable pitfall for the neuromuscular monitoring at the recurrent laryngeal nerve: In the human surgical setting, this might have resulted in the false assumption of an anatomical intact nerve. The persistence of distal electromyographic conduction strengthens the proposal to stimulate the vagal nerve as the proximal portion of the nerve as a part of a systematic protocol.

Topics: Animals; Bias; Disease Models, Animal; Electromyography; Humans; Iatrogenic Disease; Intraoperative Complications; Isoquinolines; Male; Mivacurium; Monitoring, Intraoperative; Neuromuscular Nondepolarizing Agents; Recurrent Laryngeal Nerve; Recurrent Laryngeal Nerve Injuries; Swine; Thyroid Diseases; Time Factors; Vagus Nerve; Vocal Cord Paralysis

Electromyography for the identification of the recurrent laryngeal nerve is gaining ever more acceptance in thyroid surgery. Relaxation of the patient, e.g., to improve intubation conditions for anesthesia, carries a potential risk for error.. After definite identification of the recurrent laryngeal nerve and the vagus nerve (Neurosign 100, Magstim Co., Wales), ten consecutive patients were relaxed with mivacurium and atracurium besylate at a weight-dependent ED95 dosage. After peripheral relaxation was achieved (TOF-Watch, Organon Teknika Corp., at the adductor muscle of the thumb), the signal derived via the vocal muscle was assessed acoustically in 3-min intervals by the surgeon and graphically recorded by computer (EWACS, Inomed Co.).. Complete peripheral relaxation was attained with mivacurium after 3-7 min and with atracurium after 7-11 min. A decrease in amplitude of the vocal muscle signal of >60% was recognized by the surgeon as a weakened signal and could be confirmed during an average duration of 13.3 min with mivacurium (maximum: 37 min) and 17.7 min with atracurium besylate (maximum: 23 min), respectively. Complete obliteration of the acoustic signal (<20% of the initial signal) occurred in three of six patients treated with mivacurium and in four of four patients treated with atracurium.. The accuracy of electromyography of the recurrent laryngeal nerve can be substantially impaired by the administration of relaxants. If this medication cannot be dispensed with, the surgeon must be aware of the situation. In these cases, a peripheral relaxometer should also be employed to monitor relaxation as it subsides.

Topics: Adult; Aged; Atracurium; Electric Stimulation; Electromyography; Female; Humans; Isoquinolines; Male; Middle Aged; Mivacurium; Monitoring, Intraoperative; Neuromuscular Nondepolarizing Agents; Postoperative Complications; Recurrent Laryngeal Nerve; Recurrent Laryngeal Nerve Injuries; Sensitivity and Specificity; Signal Processing, Computer-Assisted; Thyroid Diseases; Vagus Nerve; Vocal Cord Paralysis