ABSTRACT Introduction: Patients with mechanical ventilation respiratory insufficiency require strict control of parameters that indicate the presence of lung damage; One of the parameters is to assess the relationship between arterial pressure of oxygen and inspired fraction of oxygen, however, using other less invasive parameters is the current trend, such as oxygen saturation and inspired oxygen fraction. Objective: To determine the correlation between the oxygen saturation index / inspired fraction of oxygen and oxygen blood pressure / inspired fraction of oxygen in patients with respiratory insufficiency in a mechanical ventilator. Methods: An observational correlation study was performed in patients hospitalized in the Intensive Care Unit. The Pearson coefficient was measured between the variables arterial oxygen pressure / inspired fraction of oxygen and oxygen saturation / inspire...