Five-year impact of ICU-acquired neuromuscular complications: a prospective, observational study

Abstract

Purpose: To assess the independent association between ICU-acquired neuromuscular complications and 5-year mortality and morbidity. To explore the optimal threshold of the Medical Research Council (MRC) sum score, assessing weakness, for the prediction of 5-year outcomes.

Methods: Sub-analyses of a prospective, 5-year follow-up study including 883 EPaNIC patients (Early versus Late Parenteral Nutrition in Intensive Care) (Clinicaltrials.gov:NCT00512122), systematically screened in ICU for neuromuscular complications with MRC sum score ('MRC-cohort', N = 600), electrophysiology on day 8 ± 1 to quantify compound muscle action potential ('CMAP-cohort', N = 689), or both ('MRC&CMAP-cohort', N = 415). Associations between ICU-acquired neuromuscular complications and 5-year mortality, hand-grip strength (HGF, %predicted), 6-min-walk distance (6-MWD, %predicted) and physical function of the SF-36 quality-of-life questionnaire (PF-SF-36) at 5-years were assessed with Cox regression and linear regression, adjusted for confounders. The optimal threshold for MRC at ICU discharge to predict 5-year outcomes was determined by martingale residual plots (survival) and scatterplots (morbidity).

Results: Both lower MRC sum score at ICU discharge, indicating less strength [HR, per-point-increase: 0.946 (95% CI 0.928-0.968), p = 0.001], and abnormal CMAP, indicating nerve/muscle dysfunction [HR: 1.568 (95% CI 1.165-2.186), p = 0.004], independently associated with increased 5-year mortality. In the MRC&CMAP-cohort, MRC [HR: 0.956 (95% CI 0.934-0.980), p = 0.001] but not CMAP [HR: 1.478 (95% CI 0.875-2.838), p = 0.088] independently associated with 5-year mortality. Among 205 survivors, low MRC independently associated with low HGF [0.866 (95% CI 0.237-1.527), p = 0.004], low 6-MWD [105.1 (95% CI 12.1-212.9), p = 0.043] and low PF-SF-36 [- 0.119 (95% CI - 0.186 to - 0.057), p = 0.002], whereas abnormal CMAP did not correlate with these morbidity endpoints. Exploratory analyses suggested that MRC ≤ 55 best predicted poor long-term morbidity and mortality. Both MRC ≤ 55 and abnormal CMAP independently associated with 5-year mortality.

Conclusions: ICU-acquired neuromuscular complications may impact 5-year morbidity and mortality. MRC sum score, even if slightly reduced, may affect long-term mortality, strength, functional capacity and physical function, whereas abnormal CMAP only related to long-term mortality.

Keywords: Critical care outcomes; Electrophysiology; Muscle weakness; Paresis.