**3.4 Limitations of HFNC in MLS surgery**

Duration of surgery: Operation less than 30 minutes so it is not suitable for junior staff both anesthetist and operating surgeon. It leads to CO2 accumulation. It cannot be used in case of complete nasal obstruction, bleeding inside the airway & in case of Infection: opened abscess or COVID 19 patients. Also, not used in morbid obesity and predicted difficult airway.
