Mechanical Ventilation-induced Diaphragm Atrophy Strongly Impacts Clinical Outcomes.

RATIONALE: Diaphragm dysfunction worsens outcomes in mechanically ventilated patients, but the clinical impact of potentially preventable changes in diaphragm structure and function caused by mechanical ventilation is unknown. OBJECTIVES: To determine whether diaphragm atrophy developing during mechanical ventilation leads to prolonged ventilation. METHODS: Diaphragm thickness was measured daily by ultrasound in adults requiring invasive mechanical ventilation; inspiratory effort was assessed by thickening fraction. The primary outcome was time to liberation from ventilation. Secondary outcomes included complications (reintubation, tracheostomy, prolonged ventilation, or death). Associations were adjusted for age, severity of illness, sepsis, sedation, neuromuscular blockade, and comorbidity. MEASUREMENTS AND MAIN RESULTS: Of 211 patients enrolled, 191 had two or more diaphragm thickness measurements. Thickness decreased more than 10% in 78 patients (41%) by median Day 4 (interquartile range, 3-5). Development of decreased thickness was associated with a lower daily probability of liberation from ventilation (adjusted hazard ratio, 0.69; 95% confidence interval [CI], 0.54-0.87; per 10% decrease), prolonged ICU admission (adjusted duration ratio, 1.71; 95% CI, 1.29-2.27), and a higher risk of complications (adjusted odds ratio, 3.00; 95% CI, 1.34-6.72). Development of increased thickness (n = 47; 24%) also predicted prolonged ventilation (adjusted duration ratio, 1.38; 95% CI, 1.00-1.90). Decreasing thickness was related to abnormally low inspiratory effort; increasing thickness was related to excessive effort. Patients with thickening fraction between 15% and 30% (similar to breathing at rest) during the first 3 days had the shortest duration of ventilation. CONCLUSIONS: Diaphragm atrophy developing during mechanical ventilation strongly impacts clinical outcomes. Targeting an inspiratory effort level similar to that of healthy subjects at rest might accelerate liberation from ventilation.

Measuring diaphragm thickness with ultrasound in mechanically ventilated patients: feasibility, reproducibility and validity.

PURPOSE: Ultrasound measurements of diaphragm thickness (T di) and thickening (TFdi) may be useful to monitor diaphragm activity and detect diaphragm atrophy in mechanically ventilated patients. We aimed to establish the reproducibility of measurements in ventilated patients and determine whether passive inflation by the ventilator might cause thickening apart from inspiratory effort. METHODS: Five observers measured T di and TFdi in 96 mechanically ventilated patients. The probe site was marked in 66 of the 96 patients. TFdi was measured at peak and end-inspiration (airway occluded and diaphragm relaxed) in nine healthy volunteers inhaling to varying lung volumes. The association with diaphragm electrical activity was quantified. RESULTS: Right hemidiaphragm thickness was obtained on 95 % of attempts; left hemidiaphragm measurements could not be obtained consistently. Right hemidiaphragm thickness measurements were highly reproducible (mean ± SD 2.4 ± 0.8 mm, repeatability coefficient 0.2 mm, reproducibility coefficient 0.4 mm), particularly after marking the location of the probe. TFdi measurements were only moderately reproducible (median 11 %, IQR 3-17 %, repeatability coefficient 17 %, reproducibility coefficient 16 %). TFdi and diaphragm electrical activity were positively correlated, r² = 0.32, p < 0.01). At inspiratory volumes below 50 % of inspiratory capacity, passive inflation did not cause diaphragm thickening. TFdi was considerably lower in patients on either partially assisted or controlled ventilation compared to healthy subjects (median 11 vs. 35 %, p < 0.001). CONCLUSIONS: Ultrasound measurements of right hemidiaphragm thickness are feasible and highly reproducible in ventilated patients. At clinically relevant inspiratory volumes, diaphragm thickening reflects muscular contraction and not passive inflation. This technique can be reliably employed to monitor diaphragm thickness, activity, and function during mechanical ventilation.