Changes of motor nerve membrane excitability during the acute phase of critical illness

To investigate early alterations in motor nerve membrane properties during critical illness using nerve excitability testing.

Adult critically ill patients admitted to the intensive care unit were examined within 24 h of intubation (day 1) and on days 2, 5 and 10. Examinations included neurological examination, nerve excitability testing, laboratory analyses and review of medication records; and on day 10 conventional nerve conduction studies, electromyography and a fine needle muscle biopsy.

All critically ill patients (N = 26) showed nerve hypoexcitability within 24 h compared to healthy subjects, which persisted up to day 10. Additional nerve membrane depolarisation was only observed in critically ill patients with acute kidney injury (AKI) (n = 13). Four patients fulfilled the diagnostic criteria for critical illness polyneuropathy (CIP) at day 10 (15.4%), and six (23.1%) had a reduced myosin:actin ratio indicative of myosin loss consistent with critical illness myopathy.

Nerve hypoexcitability appears to be a key feature of the early phase of critical illness, whereas additional nerve membrane depolarisation is associated with AKI, which may be linked to changes in serum potassium levels.

The findings do not support CIP as predominant explanation for nerve membrane depolarisation and muscle weakness seems to be associated with myosin loss.