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  • Letter
  • Open Access

Severe and early quadriceps weakness in mechanically ventilated patients

  • 1, 2, 3Email author,
  • 1,
  • 1,
  • 1,
  • 1,
  • 1,
  • 1,
  • 1,
  • 1,
  • 1 and
  • 1
Critical Care201418:431

  • Published:


  • Chronic Obstructive Pulmonary Disease
  • Muscle Strength
  • Muscle Weakness
  • Chronic Obstructive Pulmonary Disease Patient
  • Polyneuropathy

ICU-acquired weakness has been reported in patients with prolonged mechanical ventilation [1], leading to prolonged weaning, poor quality of life after ICU discharge, and high ICU-related cost [2]. Muscle weakness is the primary manifestation of critical illness polyneuropathy or myopathy or both.

Although quadriceps strength has never been objectively quantified in the ICU, we previously evidenced quadriceps muscle weakness by using magnetic stimulation of the femoral nerve in patients with chronic obstructive pulmonary disease (COPD) and this non-invasive technique allows a non-effort-dependent assessment of quadriceps strength [3, 4]. Thus, one objective of this pilot study was to evaluate the feasibility of assessing quadriceps strength by using this previously validated technique in sedated patients on mechanical ventilation at different stages after ICU admission using magnetic stimulation of the femoral nerve. The study was approved by the ethics committee of the Institut Universitaire de Cardiologie et de Pneumologie de Québec (CER20392). Signed informed consent was obtained from relatives for all patients.

Quadriceps twitch tension (Twq) assessment was performed in 13 consecutive sedated and mechanically ventilated patients with organ failure (Table 1). Twq measurements were repeated after awakening in nine patients. Mean Twq was 1.8 ± 1.3 kg for the whole group of patients. As shown in Figure 1, Twq was two times lower in ICU patients than in COPD patients (P <0.001) and four times lower than in healthy subjects (P <0.001). Furthermore, there was no significant difference in Twq when patients were sedated or awake. The reproducibility between these two measurements was good (Figure 2). Strength measurements have been performed in patients during septic shock (n = 2) or after a dialysis session (n = 2), and a major reduction of muscle strength (Twq <1 kg) was observed in these circumstances.
Table 1

Patient characteristics at baseline



  Males/females, number


  Age, years

71 ± 9

  Body mass index, kg/m2

25 ± 4

Arterial blood gases


  PaO2, mm Hg

82 ± 34

  PaCO2, mm Hg

41 ± 8


7.43 ± 0.08

  SaO2, percentage

95 ± 2

ICU admission


  Cardiac surgery ICU

9 (69%)

  Respiratory ICU

4 (31%)




8 (62%)


11 (85%)


3 (23%)


8 (62%)

  Diabetes mellitus

4 (31%)

Risk factor for polyneuropathy


  Mechanical ventilation more than 72 hours

12 (85%)

  Suboptimal glucose controla

11 (85%)


5 (38%)

  Septic shock

6 (46%)

  Neuromuscular blocker

5 (38%)

  Risk factors, mean

3 ± 1

Duration of hospitalization before strength assessment, days

7 ± 4

Sedation condition, RASS score

-3.8 ± 1.5

Data are presented as mean ± standard deviation or as number (percentage). aSuboptimal glucose control is defined as repeated measurements of capillary or venous glucose measurements above 10 mmol/L (at least two consecutives). COPD, chronic obstructive pulmonary disease; PaCO2, arterial pressure in carbon dioxide; PaO2, arterial pressure in oxygen; RASS, Richmond Agitation-Sedation Scale; SaO2, arterial saturation in oxygen.

Figure 1
Figure 1

Quadriceps twitch tension (Twq) in ICU patients. Stimulation was applied in ICU mechanical ventilation patients who were sedated (n = 13) or awake (n = 7) (grey), patients with age-related chronic obstructive pulmonary disease (COPD) (n = 18), and healthy subjects (n = 16) (shaded). The ends of the boxes define the 25th and 75th percentiles, and a line at the median and error bars define the 10th and 90th percentiles. *Previously measured in our laboratory [3]. ns, Not significant.

Figure 2
Figure 2

Reproducibility of quadriceps twitch tension (Twq) measurements in sedated versus awake conditions. (A) Linear regression between Twq measured in sedated versus awake conditions in mechanical ventilation patients (Spearman coefficient correlation, r = 0.93, P = 0.02). (B) Bland-Altman comparison of sedated and awake Twq measurements. Limits of agreement (reference range of differences) were -1.18 and 0.98 kg. The means bias was -0.13 kg with a standard deviation of 0.47 kg.

Our results confirm the evidence of early severe muscle weakness in mechanically ventilated patients and show that measurement of muscle strength by magnetic stimulation of the femoral nerve may be useful in ICU patients, particularly for assessing recovery or the effect of therapeutic interventions, as previously suggested by Ginz and colleagues [5]. A noteworthy result is that some events (such as dialysis and sepsis) may modify the muscle strength and need to be considered when interpreting muscle strength data in this context. Our data showing that muscle weakness is an early process in the ICU favor early treatment to prevent rather than delay treatment to treat this condition.



Chronic obstructive pulmonary disease


Quadriceps twitch tension.



Funding was provided by the Canadian Foundation for Innovation (FRSQ).

Authors’ Affiliations

Centre de Recherche de l’Institut Universitaire de Cardiologie et de Pneumologie de Québec, Université Laval, 2725 chemin, Sainte-Foy, Québec, G1V 4G5, Canada
Univ Grenoble Alpes, Grenoble, HP2 38000, France
Inserm, U 1042, Avenue des Maquis du Grésivaudan, Grenoble, 38043, France


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© Vivodtzev et al.; licensee BioMed Central Ltd. 2014

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