Comparative physiological evaluation with diaphragmatic ultrasound of the application of two different oxygen-therapy techniques in patients recovering from severe exacerbation of chronic respiratory failure.

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In patients affected by severe exacerbation of chronic respiratory failure (SE-CRF), with worsened hypercapnia and respiratory acidosis, the sole oxygen therapy is not enough and a ventilatory assistance is required, most of the time through a mask or helmet, so call non-invasive ventilation. The advantage of NIV is to guarantee a ventilatory assistance, avoiding complications related to the presence of the endotracheal tube, such as ventilator associated pneumonia. Furthermore, it has been widely shown that, in patients with SE-CRF, NIV reduces the mortality rate, as opposed to invasive mechanical ventilation. However, NIV is a "bridge-therapy", applied in the attempt to permit the pharmacological treatments (i.e. antibiotics and bronchodilators) solve the underlying reason of exacerbation; afterwards, patients can be weaned from NIV, and, whenever required, starts oxygen therapy. Among devices for oxygen therapy, Venturi mask is frequently used in Intensive Care Unit (ICU), because it is possible to provide a nominal fraction of inspired oxygen (FiO2) between 24 and 60%. Recently a new device has become commercially available (Optiflow, Fisher & Paykel, New Zealand) able to provide high flow of heated and humidified gas through nasal cannula. The humidification of gas flow reduces the risk of mucosa dryness and airway muco-ciliar clearence. The use of high-flow of gas (up to 60L/min) permits to provide accurate FiO2 during all the inspiratory phase and to wash out the naso-pharyngeal dead space, in addition to the application of a minimal positive pressure. In patients with hypoxemic acute respiratory failures of mild to moderate degree, Optiflow has been shown to be better tolerated and to guarantee a better oxygenation, in comparison with Venturi mask. Moreover, in another study a high-flow oxygen-therapy system has been shown to reduce the respiratory rate in patients with CRF and the arterial partial pressure of carbon dioxide (PaCO2). Basing on these data, the Optiflow system could potentially positively influence the inspiratory effort of patients experiencing SE-CRF, when compared to Venturi mask. Though both commonly used in clinical practice, nowadays no study has compared Optiflow with Venturi mask at this regard. We aim to evaluate if some differences in respiratory effort exists between Venturi mask and Optiflow, in patients recovering from SE-CRF, through a diaphragm ultrasonogaphy evaluation.

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