General objective: comparing psychometric properties of two pain assessment scales (BPS, NVPS) in non-verbal patients under mechanical ventilation. Design: Clinical trial of type methodological. Inclusion criteria include the following: patients under ventilation; with endotracheal tube for more than 24 hours, able to listen and respond with shaking the head, eyebrows or eyes; the level of agitation and sedation between +1 and -3, according to Richmond Agitation Sedation Scale (RASS). Exclusion criteria include: patients with quadriplegia; neuromuscular dysfunction and extensive injury in face and arms. Setting and conduct: This study is done on 50 to 60 patients under mechanical ventilation, hospitalized in the adults’ intensive care unit of Alavi, Emam, and Fatemi hospitals of the Ardabil University of Medical Sciences. Before conducting the study, the procedure will be explained to the first degree relatives, and in case they agree to participate, the investigation will be carried out. In this study, two tools, "BPS" and "NVPS", will be used. Each tool will be filled independently by two raters and simultaneously carried out on a patient. Intervention: The behavior of each patient will be seen 15 minutes before, during, and 15 minutes after both nociceptive (turning and oral suctioning ) and non-nociceptive (eye care by normal saline) procedures. Main outcome measures (variables): The patient’s pain are recorded according to; two Behavioral pain scales. Then at the end of each stage the patient will be asked whether they feel pain or not. The patient’s physiological symptoms are recorded by monitoring vital signs in all the six steps. After gathering enough samples, the tools will be compared and their psychometric properties will be measured