Table 2 Inclusion and exclusion criteria

Inclusion criteria

 Patient aged 18 years or older

 Patient experiencing breakthrough pain episode with a stable dose of opioids to control background pain

 Written informed consent for participation obtained prior to any study procedures

Exclusion criteria

 Patient with mental disorder, altered mental status

 Patient has difficulty in reporting pain

 Karnofsky Performance Status Scale score under 20

 Abdominal distension or suspected bowel obstruction, air embolism, pneumothorax, decompression sickness, epilepsy, pulmonary cancer, chronic obstructive pulmonary disease and acute respiratory infection, pregnancy, severe inhalation injury; pharmaceutical or pathological pulmonary fibrosis; maxillofacial injuries

 Disease involving ear, nose, larynges, such as sinuses, middle ear