Electrophysiological studies in the critical care unit: investigating polyneuropathies.

Polyneuropathies frequently contribute to ventilator dependency and prolonged stay in the intensive care unit. As clinical examination is often limited in critically ill patients, electrophysiological studies are invaluable in establishing the diagnosis of neuropathy, determining its pathophysiology, severity and in following the patients' progression. Guillain-Barré syndrome (GBS) developing before intensive care unit admission and critical illness polyneuropathy (CIP) developing as a complication of sepsis and multiorgan failure are the commonest causes of neuropathy. Electrophysiological findings in CIP are that of an axonal neuropathy whereas the findings in GBS are usually consistent with a demyelinating neuropathy. Axonal GBS can be distinguished from CIP by the preceding illnesses, slow nerve conduction velocity in some cases, lack of spontaneous activity on the initial needle electromyographic study and cerebrospinal fluid findings.