Background: An early diagnosis of ICU-acquired weakness (ICU-AW) is difficult because disorders of consciousness frequently preclude muscle strength assessment. In this study, we investigated feasibility and accuracy of electrophysiological recordings to diagnose ICU-AW early in non-awake critically ill patients.
Methods: Newly admitted patients, mechanically ventilated ≥2 days and unreactive to verbal stimuli, were included in this study. Electrophysiological recordings comprised nerve conduction studies (NCS) of three nerves and, if coagulation was normal, myography in three muscles. Upon awakening, strength was assessed (ICU-AW: average Medical Research Council score <4), blinded for electrophysiological recordings. Feasibility was expressed as the percentage of recordings that were both possible and had sufficient technical quality. Diagnostic accuracy of feasible (i.e., feasibility >75 %) recordings was analyzed based on cut-off values from healthy controls and from critically ill patients with and without ICU-AW.
Results: Thirty-five patients were included (17 with ICU-AW). Recordings were obtained on day 4 (IQR: 3-6). Feasibility was acceptable for ulnar and peroneal nerve recordings, and low for sural recordings and myography. Diagnostic accuracy based on cut-off values from healthy controls was low. When using cut-off values from critically ill patients with and without ICU-AW, the peroneal compound muscle action potential amplitude and ulnar sensory nerve action potential amplitude had good diagnostic accuracy.
Conclusion: Nerve conduction studies of the ulnar and peroneal nerve are feasible in critically ill patients. The diagnostic accuracy is low using cut-off values from healthy controls. Cut-off values validated specifically for discrimination between critically ill patients with and without ICU-AW may improve diagnostic accuracy.