Diaphragm Ultrasound as a Powerful Tool in Managing Acute Hypoxemic Respiratory Failure in Hematological Patients

Acute hypoxemic respiratory failure due to parenchymal disfunction is one of the main complications of immunocompromised hematological patients. Mechanical ventilation is frequently needed and diaphragm activity has to be assessed not to worsen ventilator-induced lung injury.

Acute hypoxemic respiratory failure due to parenchymal disfunction is one of the main complications of immunocompromised hematological patients. In these cohort of patients mechanical ventilation is frequently needed in order to restore oxygenation and normocapnia. Since every positive-pressure ventilation regimen may potentially determine pulmonary complications, due to alteration in pressure and volume lung homeostasis and diaphragm activity, also diaphragm function has to be assessed not to worsen ventilator-induced lung injury (VILI). Main targets of VILI are pulmonary interstitium and diaphragm.

Pulmonary interstitium is frequently involved in different mechanism of injury, that derive both from induced tidal volume and positive end expiratory pressure (PEEP). Indeed, large tidal volumes generated during assisted spontaneous breathing may configure non-protective ventilation regimens and the so called "pendelluft phenomenon", that is the intrinsic flow of air within the lung from nondependent to dependent regions without changes in tidal volume, may affect inadequate PEEP values.

Positive-pressure ventilation may also alter diaphragm activity. Recent data show that diaphragm disfunction, considered as an enhanced or reduced thickening fraction, occurs in about 65% of patients undergoing mechanical ventilation.

Since the potential harm of positive-pressure ventilation, the optimization of mechanical ventilation is pivotal to ensure an adequate time-to-recovery without concurring to the onset of further lung and diaphragmatic injury. Neurally Adjusted Ventilatory Assist (NAVA) is a recent modality of mechanical ventilation that delivers ventilatory assistance according to the respiratory effort of the patient, measured by electrical activity of the diaphragm (EAdi). NAVA works proportionally with EAdi values, ensuring a better neuroventilatory efficiency compared to other mechanical ventilation modes and also reducing patient-ventilator asynchrony. According to these features NAVA protocol may be useful in preserving gas exchanges and diaphragm function both in invasive and non-invasive ventilation.

Therefore the evaluation of basal diaphragm activity, the choice of the device for oxygen support administration and the setting of ventilatory parameters may influence hospital stay and outcome of patients affected by acute hypoxemic respiratory failure.

The aim of this study is to evaluate the basal diaphragm activity of acute hypoxemic respiratory failure patients admitted in Intensive Care Unit (ICU) and to record diaphragm activity modifications during the ICU stay in relation to the optimization of medical therapy and, if necessary, according to the need of ventilatory support (invasive or non-invasive ventilation delivered with NAVA protocol).

This study intends to register also daily diaphragm thickening fraction, daily arterial blood gas analysis, failure frequency of non-invasive ventilation, frequency of tracheal intubation, length of mechanical ventilation, length of hospital stay and hospital mortality.

Eligibility Criteria:
Inclusion Criteria:

* Hypoxemic respiratory failure in hematological patients (PaO2 \< 70 mmHg or P/F \< 150)

Exclusion Criteria:

* Patients with positive-pressure ventilation regimen of high flow nasal cannula prior to ICU admission
* Unstable clinical condition (use of vasopressors, acute coronary syndrome...)
* Refusal of treatment or informed consent
* Agitation (RASS ≥+2) or lack of collaboration (Kelly Matthay ≥ 5)
* Multiple organ failure
* Enrollment in other study protocols