Background The exacerbation of respiratory failure that occurs after endotracheal intubation often occurs in patients who have received mechanical ventilation therapy, and when it occurs, it emerges as an important issue to consider reintubation of endotracheal intubation. High-flow nasal cannula (HFNC) through nasal cannula is known to produce positive airway pressure and deliver a certain amount of oxygen, and recently reported clinical studies have demonstrated the effect of lowering the risk of reintubation after endotracheal intubation, which is recommended for use in recent clinical practice guidelines. However, in patients at high risk of intubation failure, the combination of high-flow oxygen therapy and non-invasive positive-pressure ventilation therapy rather than the application of high-flow oxygen therapy alone through nasal cannula is helpful in reducing the rate of reintubation of endotracheal intubation. However, an alternative to non-invasive positive-pressure ventilation therapy is needed as there is a possibility of complications such as aspiration pneumonia, maladaptation of the application device (mask), and discomfort, making it difficult to apply it in the field.

Recently, it has been reported that high flow oxygen therapy through an asymmetric nasal cannula forms sufficient positive pressure in terms of respiratory dynamics, which makes the patient feel comfortable and reduces work of breath. However, no clinical studies have yet compared physiological effects using this method in patients at high risk of extubation failure.

Goal The investigators would like to compare the physiological effects of high flow oxygen therapy through 'asymmetric nasal cannula' with high flow oxygen therapy through 'standard nasal cannula' in patients identified as high-risk groups for valvular failure.

Hypothesis 'Asymmetric nasal cannula' reduces work of breath compared to 'standard nasal cannula' in high-risk patients with valvular failure.

Inclusion Criteria:

1. 19 years of age or older

2. Patients who applied mechanical ventilation treatment for more than 24 hours before the excision

3. Patients who underwent endotracheal intubation rather than tracheal incision

4. Planned extubation after successful spontaneous breathing trial (SBT)

5. Reintubation High Risk Patients: If any of the following conditions are met

   1. Age > 65

   2. Acute Physiology and Chronic Health Evaluation(APACHE) II on the day of extubation > 12

   3. Body mass index (BMI) > 30 kg/m2

   4. Inability to deal with respiratory secretions

      • improper cough reflex
      • If at least three aspirations are required in the 8 hours prior to the discharge

   5. Difficult or long delay in mechanical ventilation

      • The first attempt to leave the mechanical ventilation failed

   6. Charlson Commercial Index (CCI) at least 2 categories of comorbidities

   7. Heart failure is the main indication of mechanical ventilation application

   8. Moderate to severe chronic obstructive pulmonary disease

   9. If there is a problem with airway openness (high risk of developing laryngeal edema)

      • a woman
      • Oral endotracheal intubation maintenance period of at least 3 days
      • Difficult to intubate endotracheally (difficult airway)

   10. Long-term mechanical ventilation application: When applied for more than 7 days

Exclusion Criteria:

1. a patient with a tracheostomy tube

2. Contraindicated application of nasal interfaces

   • a nasal disorder

3. Continuous positive pressure (CPAP) application contraindications

   • pneumothorax, blistering lung disease, head trauma, cranial facial surgery, airway foreign matter, unstable hemodynamics, etc

4. EIT application contraindications

   • Patients using implantable electronic medical devices (such as implantable defibrillators, pacemakers or spinal cord stimulators)
   • a patient with hyperhidrosis
   • a patient whose physical movements are not controlled
   • a pregnant woman
   • BMI 50 or higher