Colonoscopy Using Nitrous Oxide- A Pilot Study in the USA

Inclusion Criteria: Men and women, more than 18 years old Scheduled for a colonoscopy at the Endoscopy unit Exclusion Criteria: * High ASA risk (IV/ \>) * History of chronic pain * Allergy to N2O or opioid or BDZ * No consent * Recent head injury with impairment of consciousness or Intracranial / Middle Ear surgery within the previous 6 months with or without residual deficits. * Pneumothorax, air embolism * Decompression sickness or within 48 hours of an underwater dive * Severe emphysema with bullae * Gross abdominal distension with suspicion for bowel obstruction * Intoxication * Maxillofacial injuries (where patient unable to administer the drug using a mouthpiece/mask, or there is the risk of causing further damage to facial wounds and there may also be a significant risk of blood inhalation) * Patients with chronic pulmonary disease for whom an inspired oxygen concentration of more than 28% oxygen might be dangerous * Patients on Methotrexate * Where patients need assistance to hold the mask or mouthpiece. * Retinal surgery within the last three months * Any patient who does not otherwise clinically qualify for standard sedation methods (i.e., those who require general anesthesia)