Diaphragm Function Assessment in Critical Care

In critically ill patients, diaphragm dysfunction is a frequent and clinically significant consequence of prolonged mechanical ventilation, sepsis and systemic inflammation. Accurate evaluation of diaphragm function is essential for optimising weaning strategies, tailoring respiratory support and guiding rehabilitation. Traditional assessment techniques include transdiaphragmatic twitch pressure elicited by phrenic nerve stimulation and maximal inspiratory pressure, both of which quantify global muscle strength but demand specialised apparatus or active patient participation. In recent years, ultrasound imaging at the zone of apposition has become a non-invasive bedside modality, enabling measurement of diaphragmatic excursion and thickening fraction to infer contractile performance. Complementary indices, such as the rapid shallow breathing index and its diaphragm-based variant, integrate respiratory rate, tidal volume or diaphragmatic displacement to enhance prediction of weaning success. Combining physiological measures with real-time imaging not only refines the prognostic accuracy for ventilator liberation but also informs interventions—such as inspiratory muscle training and adjusted ventilator settings—to mitigate ventilator-induced diaphragmatic dysfunction, reduce intensive care unit length of stay and improve patient outcomes.

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Diaphragm Function Assessment in Critical Care publication trend

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Technical terms

Diaphragmatic excursion: The amplitude of cranio-caudal movement of the diaphragm during the respiratory cycle, measured by ultrasound.

Diaphragmatic thickening fraction: The percentage change in diaphragm muscle thickness between end expiration and end inspiration, used to assess contractile activity.

Rapid shallow breathing index (RSBI): The ratio of respiratory rate to tidal volume, employed to predict success in weaning from mechanical ventilation.

Diaphragmatic rapid shallow breathing index (D-RSBI): A modified RSBI in which tidal volume is replaced by ultrasound-measured diaphragmatic displacement, improving weaning failure prediction.

References

1. Effectiveness of diaphragmatic ultrasound as a predictor of successful weaning from mechanical ventilation: a systematic review and meta-analysis. Critical Care (2023).
2. Diaphragm ultrasound as indicator of respiratory effort in critically ill patients undergoing assisted mechanical ventilation: a pilot clinical study. Critical Care (2015).
3. Diaphragm ultrasound as a new index of discontinuation from mechanical ventilation. The Ultrasound Journal (2014).
4. Inspiratory muscle strength training improves weaning outcome in failure to wean patients: a randomized trial. Critical Care (2011).
5. Can diaphragmatic ultrasonography performed during the T-tube trial predict weaning failure? The role of diaphragmatic rapid shallow breathing index. Critical Care (2016).
6. Clinical review: Ventilator-induced diaphragmatic dysfunction - human studies confirm animal model findings!. Critical Care (2011).
7. Diagnostic methods to assess inspiratory and expiratory muscle strength*. Jornal Brasileiro de Pneumologia (2015).