The primary aim of the study is to determine the rate sedation-induced adverse events, comparing BIS-guided sedation with clinical observation. Secondary outcomes were to examine patient characteristics who developed adverse events, propofol and remifentanil dosage and patient satisfaction analyzing different time points undergoing elective colonoscopy.

Randomized double-blind clinical trial in patients undergoing scheduled colonoscopies in endoscopy rooms of the Galdakao-Usánsolo Hospital (Bizkaia, Spain) and Mendaro Hospital (Gipuzkoa, Spain). The investigators will compare the rate of cardiorrespiratory adverse events as well as the anesthetic drugs dosage, need for rescue medication and patient satisfaction among the experimental group in which sedation is guided by BIS and the control group in which the anesthesiologist is blind to the result of the BIS. The investigators hypothesized that BIS monitoring would be associated with better outcomes than clinical observation.

The BIS is the parameter of anesthetic depth monitoring most used today. Its use was approved by the Food and Drug Administration (FDA) in 1996 as an aid to control the effects of certain anesthetic agents. It is validated in the operating room (Recommendation grade A), but not outside it due to lack of conclusive studies.

180 patients are needed to obtain statistically significant differences between both groups. Qualitative variables are expressed in the form of frequencies and percentages and continuous variables in the form of means and standard deviations. Comparisons of percentages will be made by the Chi square test (or Exact Fisher's test, when the expected frequencies are less than 5) and the difference of means in the continuous variables by the t test as well as by the Wilcoxon nonparametric test if the distribution of the variable requires it. The degree of agreement between the BIS and Ramsay scale will be made through the weighted Kappa test. Statistical significance will be assumed when p <0.05. All statistical analyzes will be carried out using SAS V9.4. (SAS institute, Inc., Carey, NC).

Inclusion Criteria:

• Indication of complete colonoscopy on a scheduled basis.
• Classification of physical status ASA I, II and III, with the exception of patients with moderate to severe kidney and / or liver disease.
• Intermittent or persistent mild asthma. It implies the absence of daily symptoms and FEV1> 80% (GINA 2004).
• Body Mass Index (BMI) less than 35 kg / m2, and greater than 18 kg/m2.
• Intact neurological capacity.
• Acceptance to participate in the study after the contribution of written informed consent.

Exclusion Criteria:

• ASA IV.
• BMI greater than 35 kg / m2, and less than 18 kg/m2.
• Refusal to participate in the study.
• Allergy to any of the medications used in sedation, or its components.
• Known mental or neurological disease.
• Renal and / or moderate to severe Hepatic insufficiency.
• Chronic Obstructive Pulmonary Disease (COPD) or Obstructive Sleep Apnea.
• Chronic opiate users.

The investigators have a randomization table to assign the intervention of each patient. The investigators will record anthropometric data and the parameters resulting from the monitoring. These data will be available to collaborating investigators and subsequently to a member of the Research Unit who will record this information in a database that will be analyzed to obtain results.

This study will begin in January 2018 and will end after the recruitment of the 180 patients and subsequent data analysis, approximately in June 2020.

The Principal Investigator has produced an Information Manual for collaborators where the protocol and the objectives of the study are detailed. This information has been sent via email and is printed and available in the endoscopy room where the registration will take place. The information folder includes the randomization table, informed consent, patient information sheet, data record sheet and record sheet for the BIS parameters of the patients in the Ramsay group. This information has been transmitted orally and an informative session has been held for all the members of the project.

Members of the Research Unit will perform a check of this information, correlating it with what is described in the anesthesia chart and reviewing the patient data in the health system database. In addition, they will collaborate with the statistical analysis and obtaining results.

Patients will be randomly assigned to one of the two study groups. The anesthesiologist who records the information knows which group they belong to, according to a randomization table provided in collaboration with the Research Unit, but the patients do not know it.