During anesthesia, EEG shows specific and significant changes according to the depth of anesthesia and the drugs used. Endoscopic procedures like gastroscopies or colonoscopies are usually done on an outpatient basis using essentially propofol for sedation or anesthesia. Preliminary reports have shown that the depth of anesthesia during these procedures may be very deep resulting even in a burst suppression pattern on the EEG.

In this study, frontal EEG will be recorded continuously using a Root - Sedline device (Masimo, US). Anesthesiologists will be free to use the medications and dosage they judge appropriate. The attending anesthesiologist will be blinded to the EEG. Medications and dosages will be recorded, as well as processed EEG data from the Sedline and the raw EEG. Primary outcome is the % of time spend in specific range of patient state index (PSI 0-10; 10-20; 20-30; 30-40; 40-50; 5-60; 60-70; 70-80; 80-90; 90-100) as well as the % of time spent in burst suppression.

Inclusion Criteria:

• Patients undergoing gastroscopy and or colonoscopy in a outpatient setting under sedation or general anesthesia

Exclusion Criteria:

• Patients < 18 years
• altered renal function, Glomerular filtration rate < 50 mL/min/m2
• altered hepatic tests, > 1.5 * upper normal limit
• Any form of hepatic cirrhosis
• Presence of oesophageal varices
• Any neurological pathology rendering EEG analysis non reliable