The following patients were excluded: allergy to soybeans, nitrites, egg products and propofol; combined with heart diseases, which were symptomatic upon transnasal gastroscopy; contraindicated for nitrous oxide inhalation and transnasal gastroscopy; planning pregnancy or during the first 3 months of pregnancy;
comatous state, within one week after pneumoencephalography, middle ear diseases, aerothorax, pulmonary cystic fibrosis, bowel obstruction, having received nasal sinus surgery or nasal septum surgery, oxygen saturation below 95%, systolic pressure below 90mmHg.