Acute pneumothorax occurring under general anaesthesia with positive pressure ventilation especially when using nitrous oxide can rapidly become life­threatening tension pneumothorax. As the diagnosis is often difficult or delayed in this situation, a high index of suspicion and clinical examination aided by monitors are necessary for the diagnosis, which may be confirmed by radiography or ultrasonography. Immediate stoppage of nitrous oxide with prompt release of the pneumothorax by needle aspiration or intercostals drainage is needed to save the life of the patient. This is a case report of an un­anticipated acute pneumothorax which occured soon after the induction of general anaesthesia, which was diagnosed and managed successfully in time.

Keywords: Acute Pneumothorax; General Anaesthesia; Nitrous Oxide.