Neuromuscular electrical stimulation for early rehabilitation in critically ill patients: a systematic review of applied protocols

INTRODUCTION: Neuromuscular electrical stimulation (NMES) is increasingly used to mitigate negative consequences of bed rest in critically ill patients, especially those unable to actively participate in mobilization. However, existing studies have shown inconsistent outcomes, potentially due to heterogeneous NMES protocols. This systematic review aimed to identify and characterize the NMES protocols applied in this context. METHODS: A systematic literature search was conducted in MEDLINE, Cochrane Library, Pedro, and CINAHL up to August 18, 2025. Studies were selected based on predefined PICOS criteria, focusing on adult intensive care unit (ICU) patients receiving NMES for early rehabilitation. Only randomized controlled trials and observational studies were included. Data on protocol parameters and patient characteristics were extracted and descriptively analyzed. RESULTS: 44 studies with a total of 2,553 patients were included, applying 50 different NMES protocols. Stimulation predominantly targeted lower limb muscles using biphasic rectangular waveforms. Pulse duration ranged from 250–1,400 µs, frequencies from 20–121 Hz, and intensities from 2–250 mA or 20–250 V. Considerable heterogeneity was observed in stimulation settings, reporting methods, and protocol transparency. CONCLUSION: The reviewed studies highlight the lack of standardization in NMES protocols for ICU patients. Variability in stimulation parameters hinders comparability and clinical translation. Future research should aim to harmonize protocols respectively their reporting to strengthen the comparability of clinical studies and their outcomes.