Respiratory failure is one of the common critical illnesses. So, what are the clinical manifestations of respiratory failure? Firstly, there is difficulty breathing, which is the most common symptom of respiratory failure. Most patients experience noticeable difficulty breathing, and in severe cases, patients may sit upright to breathe, sweat profusely, and appear very distressed. Another symptom is cyanosis, a typical sign of oxygen deficiency. Mild cases may show cyanosis at the extremities and lips, while severe cases can exhibit cyanosis throughout the body. Additional symptoms can include neurological and psychological symptoms such as confusion, mania, convulsions, coma, and drowsiness. Due to the oxygen deficiency affecting various systems, other systems may also show corresponding symptoms, such as tachycardia and arrhythmia in the circulatory system, and potential upper gastrointestinal bleeding in the digestive system.