suction can be several complications including pain and increased intracranial pressure and consequently the associated loss of consciousness. The aim of this study was to compare the effect of open endotracheal tube suction catheter with two different sizes 12 and 14 on the pain and level of consciousness intensive care units. In this clinical trial 36 patients in one group and under suction catheter with two sizes 12 and 14, respectively. Episodes of pain in the first to three were evaluated based on the criteria Cpot. Changes in level of consciousness, coma new 4-point criteria measured and recorded. Paired t-test to compare changes and the correlation between pain and average pain level of consciousness of the Pearson correlation coefficient was used. In the third episode, pain during suctioning had the highest score and this amount was significant difference between large and small catheter (p = 0.000). A significant relationship between pain and mental status changes were observed in any of the episodes suction. Using a small catheter to suction pressure in the brain and lead to smaller changes in level of consciousness, so to catheters in intensive care unit patients is recommended.