Sedation is a basic and necessary procedure in the intervention of the critical ill patient in the Intensive Care Unit (UCI), and specially of the patient who requires ventilation support. Sedation's objective is keeping the patient relaxed, and cooperative to treat his/her pathology. The assessing of the state of sedation is an activity of nursing staff, so it is essential to have instruments validated and appropriated for the correct assessment of patients, facilitating the manipulation, management and treatment, improving the prognosis, reducing risks of extubation or reducing their hospital permanence. In the present study, the nursing staff had the opportunity to apply two sedation assessment scales (Ramsay or Richmond sedation scales), the objective was to choose which of the two is the most appropriate for the evaluation of adult patients in critical state under sedation. To achieve this a questionnaire adapted from a UK study was used. The questionnaire was applied to 30 nurses in two Intensive Care Units of General Hospitals in Mexico State. The main variables measured were the level of knowledge of the same, professional experience and the level of studies. The results obtained did not show statistical significance among variables of the level of knowledge; however, in relation to the professional experience and the knowledge about the scales the results showed a relationship with statistical significance. Most of nurses preferred the Richmond scale to assess levels of agitation relative to the variable level of knowledge. In the sedation level did not obtain statistical significance in the preference for one scale.