Differential contractile response of critically ill patients to neuromuscular electrical stimulation

Abstract

Background: Neuromuscular electrical stimulation (NMES) has been investigated as a preventative measure for intensive care unit-acquired weakness. Trial results remain contradictory and therefore inconclusive. As it has been shown that NMES does not necessarily lead to a contractile response, our aim was to characterise the response of critically ill patients to NMES and investigate potential outcome benefits of an adequate contractile response.

Methods: This is a sub-analysis of a randomised controlled trial investigating early muscle activating measures together with protocol-based physiotherapy in patients with a SOFA score ≥ 9 within the first 72 h after admission. Included patients received protocol-based physiotherapy twice daily for 20 min and NMES once daily for 20 min, bilaterally on eight muscle groups. Electrical current was increased up to 70 mA or until a contraction was detected visually or on palpation. Muscle strength was measured by a blinded assessor at the first adequate awakening and ICU discharge.

Results: One thousand eight hundred twenty-four neuromuscular electrical stimulations in 21 patients starting on day 3.0 (2.0/6.0) after ICU admission were included in this sub-analysis. Contractile response decreased from 64.4% on day 1 to 25.0% on day 7 with a significantly lower response rate in the lower extremities and proximal muscle groups. The electrical current required to elicit a contraction did not change over time (day 1, 50.2 [31.3/58.8] mA; day 7, 45.3 [38.0/57.5] mA). The electrical current necessary for a contractile response was higher in the lower extremities. At the first awakening, patients presented with significant weakness (3.2 [2.5/3.8] MRC score). When dividing the cohort into responders and non-responders (> 50% vs. ≤ 50% contractile response), we observed a significantly higher SOFA score in non-responders. The electrical current necessary for a muscle contraction in responders was significantly lower (38.0 [32.8/42.9] vs. 54.7 [51.3/56.0] mA, p < 0.001). Muscle strength showed higher values in the upper extremities of responders at ICU discharge (4.4 [4.1/4.6] vs. 3.3 [2.8/3.8] MRC score, p = 0.036).

Conclusion: Patients show a differential contractile response to NMES, which appears to be dependent on the severity of illness and also relevant for potential outcome benefits.

Trial registration: ISRCTN ISRCTN19392591 , registered 17 February 2011.

Keywords: Critical illness; Critical illness myopathy; Early mobilisation; Intensive care unit-acquired weakness; Neuromuscular electrical stimulation.

Conflict of interest statement

The authors declare that they have no competing interests.

Figures

Fig. 1

Relative contractile response, electrical current and muscle strength during NMES. a Relative contractile response decreases between day 1 and day 7 without reaching statistical significance. b Upper extremities show a significantly higher response rate to NMES on days 1, 2, 3, 4, 5 and 7 in comparison to lower extremities. c Muscle strength and contractile response for all muscle groups separately. M. vastus lateralis shows the lowest response to NMES. d Electrical current required to elicit a muscle contraction remains unchanged between day 1 and day 7. e A significant difference in electrical current required to elicit a muscle contraction can be observed on days 2, 3, 4, 5 and 6 when comparing upper and lower extremities. f Muscle strength increase for both extremities between first awakening and ICU discharge does not reach statistical significance. g The increase in muscle strength between first awakening and ICU discharge reaches statistical significance for lower extremities. All values are shown as median and interquartile range. Statistical significance was calculated via Mann-Whitney U test or Wilcoxon signed-rank test as appropriate. A p < 0.05 is indicated by "+" in b and e. ICU = intensive care unit; MRC = Medical research council

Fig. 2

Relative contractile response, electrical current and muscle strength in comparison between responders and non-responders. Relative contractile response is significantly higher in responders as opposed to non-responders during the first 7 days after ICU admission a for both extremities, b for upper extremities, c for lower extremities and d for all muscle groups separately. Electrical current required to elicit a contractile response is significantly higher in non-responders as opposed to responders during the first 7 days after ICU admission e for both extremities and f for upper extremities, while no difference can be observed for g lower extremities. Muscle strength measured via MRC scored at ICU discharge shows significantly higher values in responders as opposed non-responders for i upper extremities, while not reaching statistical difference for h both extremities as well as j lower extremities at first adequate awakening as well as ICU discharge and h upper extremities at first adequate awakening. All values are shown as median and interquartile range. Statistical significance was calculated via Mann-Whitney U test or Wilcoxon signed-rank test as appropriate. MRC = Medical research council

Fig. 3

Muscle strength at first adequate awakening and ICU discharge for all muscle groups separately. Muscle strength difference measured via MRC score at a first awakening and b ICU discharge in responders and non-responders. MRC = Medical research council

Fig. 4

Correlation and ROC curve for contractile response and SOFA. Relative contractile response between days 1 and 7 correlates with a SOFA score. b ROC curve for SOFA score in patients with adequate contractile response to neuromuscular electrical stimulation. SOFA = Sepsis-related Organ Failure Assessment; ROC = receiver operating characteristics