Insufflation is essential procedure to observe the lumen of gastrointestinal tract in gastroscopy or colonoscopy Currently, most of hospital in Korea are using room air for insufflation According to recent clinical studies have shown that carbon dioxide have better safe and reduce stomachache than room air when endoscopy and endoscopic procedure is performed.

However, there was still no research data or study in Korea. In this study, the investigators will try to make comparison between Carbon dioxide and room air insufflation for endoscopic submucosal dissection for Gastric Tumor and investigate the efficacy and safety

Inclusion Criteria:

• Patients who have gastroscopy and colonoscopy or ESD for gastric tumor under sedation in department of gastroenterology, Gachon University Gil Medical Center

Exclusion Criteria:

• Age : < 19 years old
• Underlying disease : COPD requiring O2
• Known CO2 retention
• Opiate abuse for chronic pain
• Nonreader or short in understanding
• Pregnancy
• Any medical instabilities expected to not be in safe