High-flow nasal oxygenation in sedated lung transplant patients during transbronchial biopsy

Post-lung transplant bronchoscopy is a commonly performed diagnostic procedure to facilitate tissue sampling for rejection and infection surveillance. Sedation is used during the procedure to optimise procedural conditions and patient comfort. Oxygenation is routinely provided by standard nasal cannula at flow rates of 4-10L/min. However procedural desaturations are not infrequent. This not only represents an obvious risk to the patient but, due to the shared airway, can also prolong the procedure if bronchoscopy must be halted whilst the patient is ventilated. Recently high flow nasal cannula (HFNC) has been investigated as a safe alternative to standard low flow oxygenation via nasal cannula (LFNC) during endobronchial ultrasound under conscious sedation. HFNC, delivering 30-70L/min of humidified oxygen, improved the lowest recorded oxygen saturation during the procedure. However, this method has not been trialled in lung transplant patients undergoing transbronchial biopsy. This trial will assess the use of HFNC oxygenation as a safe and effective alternative to LFNC oxygenation in sedated lung transplant patients undergoing diagnostic transbronchial biopsy. Patients will be randomised to either the intervention, HFNC, or control, LFNC, group. The participant, research assistant and bronchoscopist will all be blinded to the intervention. For both practical and safety reasons, the Anaesthetist will not be blinded. The anaesthetist will be responsible for opening the sealed envelope and ensuring the participant receives the correct oxygen flow rate. All participants will receive a standardised anaesthetic consisting of pre-oxygenation (at 4 litres/minute via nasal cannula), premedication with midazolam and alfentanil, topicalisation to the airway with a lidocaine nebuliser and ongoing sedation via a propofol infusion by Target-Controlled Infusion. The anaesthetic will be delivered by one of three senior consultant anaesthetists experienced in providing sedation for bronchoscopies using this method. High flow nasal cannula oxygenation (flow rates of 30-50L/min) will be delivered throughout the bronchoscopy (for approximately 30-60 minutes), in the operating, using the Optiflow Nasal High Flow Cannula (Fisher & Paykel, Auckland New Zealand). The flow rates will be set at the start of the procedure and may be adjusted at the discretion of the treating anaesthetic consultant.