Methods.

Direct muscle stimulation was performed in paralyzed or extremely weak muscles. EMG was performed on each muscle before direct stimulation to determine the amount of spontaneous activity present and whether voluntary motor units could be recruited in the muscle. For stimulation, a stainless steel subdermal electrode (12 mm in length, 0.4 mm in diameter, Nicolet Biomedical, Madison, WI) was placed in the distal third of the muscle, away from the end-plate region. Another subdermal needle was placed 5 mm laterally as an anode. The muscle was stimulated with gradually increasing strength until a clear twitch was palpable (10-100 mA, 0.1 msec, 0.5 Hz). Guided by the twitch, we placed a recording needle (stainless steel subdermal electrode, 12 mm in length, 0.4 mm in diameter, Nicolet Biomedical) 1 to 3 cm away from the stimulation electrode and moved it until we maximized the amplitude of the CMAP. A surface electrode was used as a reference. The signals were amplified and bandpass filtered (20 Hz to 10 kHz). Using this technique we could obtain CMAPs in electrically excitable muscle with amplitudes from 0.5 to 10 mV. The advantage of this stimulation technique is that large regions of muscle are activated, making it difficult to miss small regions of excitable muscle. Even in muscles with small compound action potentials, moving the recording electrode 1 cm away from the muscle twitch did not markedly reduce the action potential amplitude. In muscles in which no twitch could be obtained, the recording needle was placed within 1 cm of the stimulating electrode and moved 180 degrees around the stimulating electrode with the sensitivity on 500 mu V per division to make certain that a small CMAP was not missed.

Case Reports.

Patient 1.

A 67-year-old man with a history of prostate cancer and right brachial plexopathy secondary to birth trauma was in good health until 1 day prior to admission, when he developed shortness of breath. The shortness of breath rapidly worsened and he was admitted the next day with respiratory failure. He was treated with multiple antibiotics and 3 doses of 35 mg of methylprednisolone and was sedated and paralyzed with vecuronium for 6 days (total dose of vecuronium, 584 mg). The etiology of his acute respiratory failure was never fully determined, although mitral regurgitation was thought to have played a role. One month into his hospital course he underwent uneventful mitral valve replacement.