Inclusion Criteria:  Patients must be 18 years of age or older, and scheduled for an elective colorectal procedure at London Health Science Center (LHSC). Informed consent must be obtained.  Exclusion Criteria:  Patients unable to perform written consent will be excluded. The investigators will not include colorectal procedures performed for urgent or emergent indications. Patients with advanced pulmonary disease necessitating home oxygen pre-operatively will be excluded. Patients that are pregnant will be excluded.