Relationship between Amplitude of Compound Muscle Action Potential and Muscle Strength in Critically Ill Patients with Paralysis

  Objective  To investigate the relationship between amplitude of compound muscle action potential (CMAP) and muscle strength in critically ill patients with paralysis.

  Methods  Motor nerve conduction study was performed in 30 critically ill patients with paralysis. Muscle strength was evaluated at the same time. The relationship between the amplitude of CMAP and muscle strength was analyzed.

  Results  Amplitude of CMAP and motor conduction velocity was normal in 5 patients with paralysis, including 3 with significant muscle weakness. The detection results supported the diagnosis that the lesions were located in central nervous system. Six patients with significant muscle weakness had motor never conduction block, slow conduction velocity, and decreased amplitude, which supported the diagnosis of demyelinating neuropathy. Nineteen patients had decreased amplitude of CMAP, including obviously decreased amplitude in 8 patients (no response in 3 patients). Physical examinations identified 8 patients with significant muscle weakness, 10 with mild weakness, and 1 with normal muscle strength, which confirmed the diagnosis of neuromuscular disease.

  Conclusion  The combined assessment of muscle strength and amplitude of CMAP is helpful for the diagnosis of critically ill patients with paralysis, especially for those with significant muscle weakness.