The purpose of the study is to evaluate variation of BNP in non invasive mechanical ventilated patients with severe acute respiratory failure.

The aim of the study is to evaluate in patients with severe acute respiratory failure requiring non invasive mechanical ventilation BNP levels at admission and during the following 24 hours during non invasive mechanical ventilation (Non Invasive Positive Pressure Ventilation or Continuous positive airway pressure).

Because in patients affected by acute respiratory failure it is often difficult to distinguish if the disease precipitating the respiratory failure is a cardiac disease or a lung disease, aim of the present study is to evaluate the discriminating role that BNP could have in this group of patients; evaluation will be completed, once obtained clinical stabilisation, with an echocardiography and respiratory functional test.

Inclusion Criteria:

• Severe respiratory distress (use of respiratory accessory muscles);
• Respiratory rate > 25 per minute;
• Respiratory acidosis (pH < 7.35 and PaCO2 > 45 mmHg);
• PaO2/FiO2 < 250

Exclusion Criteria:

• Age < 18 years;
• Facial deformities;
• Pneumothorax;
• Shock or systolic arterial pressure below 90 mmHg with amine infusion;
• Life-threatening arrhythmias;
• Need for immediate endotracheal intubation (PaO2/FiO2 < 100 with FiO2 100%, respiratory rate < 10, GCS < 8);
• Lack of co-operation from the patient;
• Recent esophageal-gastric surgery;
• Inability to clear secretions;
• Drugs that may interfere with BNP secretion;
• Severe obesity;
• Hepatic cirrhosis with ascitis;
• Endocrine disease.

Patients of the city of Torino, admitted to the emergency department for acute respiratory failure.