Brain consumes 20% of the total oxygen within our body. The most of it used to produce ATP. High consumption of oxygen and absence of oxygen reserves will cause the cessation of active brain perfusion in an unconscious state. If blood flow does not return within 3-8 minutes, ATP reserves will decrease and causing permanent cell damage. NIRS is a non-invasive monitoring technique to measure cerebral oxygen saturation, the product of this cerebral oximeter is INVOS 4100. Dexmedetomidine (DEX) is a selective 2- adrenoreceptor agonist that has sedation effect, analgesics, anti-anxiety and sympathetic nervous inhibition, DEX also has a neuroprotective effect by producing 2 receptor that is mediated by tyrosine kinase receptor. An increase in rSO2 was found after administration of dexmedetomidine sedation. The combination of dexmedetomidine and fentanyl was found to have a good sedative effect and more controlled hemodynamics in CPB surgery. Methods: This study is an observational analytic study with a prospective cohort design. The sample were patients who were treated by ventilator on the ICU of general hospital Haji Adam Malik Medan. This study uses consecutive sampling technique to gain the total of the sample. All of the sample will be given dexmedetomidine and fentanyl then we will monitor the sample every 6 hours for 24 hours then the data will be analyzed. Result: The result of the paired T-test and Wilcoxon test are there is a significant difference between before and

Keywords : Dexmedetomidine, Fentanyl, INVOS, oxygenation, combination.