Diaphragm weakness is a common problem in ventilated patients and impedes liberation from the ventilator. We have developed an innovative technique for monitoring patient inspiratory effort and measuring diaphragm thickness under mechanical ventilation. We demonstrated the feasibility and reliability of this technique. We then employed this technique to demonstrate that diaphragm thickness changes rapidly during early mechanical ventilation and that maintaining normal inspiratory effort levels might prevent these changes. Our ultrasound technique can be widely adopted as a non-invasive method to diagnose diaphragm weakness and to titrate ventilator support to prevent diaphragm weakness and accelerate liberation from the ventilator.

Many mechanically ventilated patients develop marked diaphragm dysfunction and cannot tolerate breathing without ventilator assistance. This prolongs hospital stay and increases the risk of complications such as infection and immobility. Evidence from animal models and biopsies of the diaphragm in mechanically ventilated patients suggest that mechanical ventilation itself can cause diaphragm injury and dysfunction. This raises the spectre of a vicious cycle where acute respiratory failure renders patients ventilator-dependent, and ventilation causes diaphragm weakness which further perpetuates ventilator dependence. The diaphragm is challenging to assess: traditional monitoring techniques require invasive measurements. We evaluated a novel non-invasive ultrasound technique for assessing the diaphragm. A high frequency linear array ultrasound transducer (similar to that employed for central line insertion) is allows bedside clinicians to visualize the diaphragm in cross-section. This permits measurement of the thickness of the muscle to detect the development of muscle atrophy. Under mechanical ventilation it is often difficult to assess whether the patient is making any inspiratory efforts. Ultrasound solves this problem by detecting thickening of the muscle during each breath (which reflects inspiratory contraction of the muscle by the patient). This technique also enables non-invasive measurement of diaphragm function which aids clinicians in evaluating the reasons for difficult weaning from the ventilator. We employed this technique in a large clinical study to demonstrate for the first time that changes in diaphragm thickness are common during ventilation and that maintaining normal levels of inspiratory effort under ventilation might prevent such changes in thickness and accelerate liberation from the ventilator.