Breathing assistance apparatus

The present invention relates to the delivery of high flow humidified pressurised oxygen and/or air to a patient by way of a wide bore nasal cannula (30). The cannula of the present invention comprises wide bore cannula to minimise the flow resistance and the entry velocity. The nasal cannula includes two nasal prongs (40, 41) fittable into a patient's nostrils. The prongs follow the inner shape of the patient's nostrils such that a more efficient flow of gases into the patient's lungs is achieved as gases flow are directed down the main nasal passage more accurately. The cannula do not seal within the nasal cavities of the patient, and in some embodiments the cannula may be provided with a pressure relief valve to allow gases to be exhausted from the cannula.