The lumbar paravertebral region provides a novel site to assess neuromuscular block at the diaphragm

Purpose: We evaluated a novel, paravertebral site for assessment of neuromu scular block at the diaphragm. The neuromuscular blocking effect of 0.1 mg. kg(-1) cisatracurium at the adducting laryngeal muscles. the diaphragm and the adductor pollicis (AP) were compared. Methods: In 24 patients undergoing thyroid surgery, evoked responses from t he adducting laryngeal muscles and the AP muscle were obtained using surfac e electromyography (EMG), Skin electrodes were placed paravertebrally near T12/L1 or L1/L2 (novel position: n = 12) or conventionally (n = 12). After stimulation of the recurrent laryngeal, phrenic and ulnar nerves, the lag, onset time and maximum effect were measured (0.1 Hz. single twitch) as well as the time to reach 25% of T1/T0 CT 25%) using train-of-four stimulation every 20 sec. Results: A mean maximum block of more than 94% was reached at all sites. La g, onset time and T 25% at the adducting laryngeal muscles and the diaphrag m were significantly (P <0.005) shorter than at the AP muscle and did not d iffer significantly between the two diaphragmatic monitoring sites (convent ional: 64 <plus/minus> 21 sec, 166 +/- 41 sec and 20 +/- 3 min vs novel: 60 +/- 16 sec, 161 +/- 40 sec and 22 +/- 2 min respeaively), Conclusion: Onset and duration of action of 0.1 mg.kg(-1) cisatracurium was shorter at the larynx and the diaphragm than at the AP muscle. EMG results obtained from the novel. paravertebral site did not differ from the conven tional monitoring site at the seventh or eighth intercostal space and sugge st this alternative site is appropriate for monitoring of the diaphragm.