Early electrophysiological diagnosis of ICU-acquired weakness

Introduction

An early diagnosis of ICU-acquired weakness (ICU-AW) is difficult because disorders of consciousness preclude strength assessment [1]. Electrophysiological (EMG) studies may be an alternative approach [2]. In this study we investigated feasibility and diagnostic accuracy of EMG studies to diagnose ICU-AW in unconscious patients.

Methods

Newly admitted unconscious ICU patients (RASS <-3), ventilated for ≥2 days, were included in this single-center prospective cohort study. EMG testing included ulnar (motor/sensory), peroneal (motor) and sural (sensory) studies. Myography was performed when coagulation was normal (dorsal interossei I/II, deltoid and tibial muscles). Reliability of results was checked by an experienced neurophysiologist, blinded for strength. Motor/sensory studies were abnormal if amplitudes were below the 2.5th percentile reference values [3]. Myography was abnormal if spontaneous abnormal activity was found in ≥1 muscles. Upon awakening, strength was assessed (ICU- AW: average MRC <4 [1]), blinded for EMG. Feasibility was determined as the percentage of measurements that could be performed and were reliable. Diagnostic accuracy was analyzed using sensitivity and specificity.

Results

We included 35 patients (ICU-AW: 17). EMG testing was done on day 4 (IQR: 3 to 6). Feasibility was 94%, 89%, 77%, 34% and 31% for ulnar motor, peroneal motor, ulnar sensory, sural sensory and myography studies, respectively. Figure 1 displays amplitude values. Sensitivity/specificity was 100%/0%, 100%/31%, 31%/100%, 50%/25% and 67%/38%, respectively.

Figure 1

Dotted lines represent 2.5th percentile reference values [3].

Conclusion

Feasibility of ulnar and peroneal studies was acceptable; feasibility of sural and myography studies was low. Diagnostic accuracy was low for all studies. This may be improved with new reference values.