Evaluation of Remifentanil and Dexmedetomidine in Patients With Noninvasive Mechanical Ventilation Intolerance

Inclusion Criteria: * Sign the informed consent form voluntarily and follow the plan requirements; * Age from 18 to 75 years old (including 18 and 75 years old), regardless of gender; * Patients who received non-invasive mechanical ventilation after cardiac surgery and were intolerant of non-invasive ventilation. Exclusion Criteria: * A history of allergy to any component of the study drug; * Visual analogue scale of pain (VAS) score \>4； * Who had taken dexmedetomidine within 8 hours prior to the study; * Who had used remifentanil within 2 hours before the study began; * Expectoration difficulties; * Women who are pregnant or lactating; * Coma or uncontrollable convulsions; * Have a history of mental illness or cognitive impairment; * Delirium before the study began; * Patients with severe liver dysfunction (CTP grade C); * Patients with renal insufficiency (patients receiving renal replacement therapy); * Preoperative left ventricular ejection fraction (LVEF) \< 30%; * History of drug and alcohol abuse; * Other conditions that the investigator deems inappropriate for participation in this clinical trial.