<qa>  What is the main cause of dyspnea in mechanically ventilated ICUIntensive care unit ICU patients are continuously exposed to various unpleasant sensations that are as many sources of discomfort. If, growing attention has been given to the detection and treatment of pain, very little attention has been given to dyspnea. However, there is growing evidence suggesting that dyspnea is frequent and severe in mechanically ventilated ICU patients. In mechanically ventilated ICU patients, dyspnea is independently associated with anxiety and mechanical ventilation itself. Indeed, an optimization of ventilator settings alleviates dyspnea in 35 of patients. 