Predominant involvement of motor fibres in patients with critical illness polyneuropathy

Critical illness polyneuropathy (CIP) is a recognized cause of muscleweakness and failure of weaning from a ventilator. In order to characterizethe features of CIP, we have examined 28 consecutive surgical patients withsevere sepsis using bedside electrophysiology. Of the 28 patients (medianAPACHE II score 31), 20 developed moderate to severe CIP, as shown by thepresence of moderate to severe denervation activity on resting EMG. Themedian nerve compound muscle action potential (CMAP) amplitudes werereduced to 3.24 (SEM 0.48) mV, while sensory nerve action potential (SNAP)amplitudes obtained from the same nerve were normal (13.1 (1.9) microV). Inapproximately 50% of these patients, the reduction in CMAP exceeded 50% ofthe lower limit of normal. Similar results were obtained from stimulationof the ulnar nerve. We conclude that CIP is a major complication inpatients with severe sepsis and prolonged artificial ventilation. Itpredominantly involves motor fibres and thus markedly interferes withweaning from the ventilator.