HFNC During Bronchoscopy for Bronchoalveolar Lavage

Overview

The execution of diagnostic-therapeutic investigations by bronchial endoscopy can expose the patient to acute respiratory failure (ARF). In particular, the risk of hypoxemia is greater during broncho-alveolar lavage (BAL). For this reason, oxygen therapy is administered at low or high flows during the course of bronchoscopic procedures, in order to avoid hypoxemia. Few clinical studies have demonstrated the efficacy and safety of high flow oxygen through nasal cannula (HFNC) during BAL procedures, and no study has evaluated, during bronchial endoscopy, the effects of HFNC on diaphragmatic effort (assessed with ultrasound) and aeration and ventilation of the different lung regions (assessed with electrical impedance tomography). Therefore, investigators conceived the present randomized controlled study to evaluate possible differences existing during bronchoscopy between oxygen therapy administered with HFNC and conventional (low-flow) oxygen therapy, delivered through nasal cannula.

Patients with Acute Respiratory Failure may sometimes require a bronchial endoscopy for broncho-alveolar lavage (BAL). During the procedure, hypoxemia may worsen and oxygen may be require to avoid desaturation. In the recent years, High-Flow through Nasal Cannula (HFNC) has been introduced in the clinical practice. HFNC delivers to the patient heated humidified air-oxygen mixture, with an inspiratory fraction of oxygen (FiO2) ranging from 21 to 100% and a flow up to 60 L/min through a large bore nasal cannula. HFNC has some potential advantages. First of all, HFNC provides heated (37°C) and humidified (44 mg/L) air-oxygen admixture to the patient, which avoids injuries to ciliary motion, reduces the inflammatory responses associated to dry and cold gases, epithelial cell cilia damage, and airway water loss, and keeps unmodified the water content of the bronchial secretions. Second, HFNC determines a wash out from carbon dioxide of the pharyngeal dead space. Third, HFNC generates small amount (up to 8 cmH2O) of pharyngeal pressure during expiration, which drops to zero during inspiration. Fourth, HFNC guarantees a more stable FiO2, as compared to conventional oxygen therapy. Whenever the inspiratory peak flow of a patient exceeds the flow provided by a Venturi mask, the patient inhaled also part of atmospheric air. Electrical impedance tomography (EIT) is a noninvasive imaging technique providing instantaneous monitoring of variations in overall lung volume and regional distribution of ventilation, as determined by variations over time in intrathoracic impedance, which is increased by air and reduced by fluids and cells. EIT allows determining changes in end-expiratory lung impedance (EELI), a surrogate estimate of end-expiratory lung volume, assessing global and regional distribution of Vt, and obtaining indexes of spatial distribution of ventilation. Diaphragm ultrasound is a bedside, radiation free technique to assess the contractility of the diaphragm and the respiratory effort. In this study investigators aim to evaluate possible differences existing during bronchoscopy between oxygen therapy administered with HFNC and conventional (low-flow) oxygen therapy, delivered through nasal cannula in terms of respiratory effort (as assessed through diaphragm ultrasound), lung aeration and ventilation distribution (as assessed with EIT) and arterial blood gases.