Conventional supplemental oxygen therapy (COT) during upper gastrointestinal (UGI) endoscopy via nasal catheter is considered the standard practice in maintenance of oxygenation and prevention of hypoxia. However, it is still unclear if this oxygen delivery method is optimal in a prolonged (more than 15 minutes) procedure in patients admitted to the ICU. Because of shortage of data in this concern, this prospective, randomized, controlled clinical trial study will aim to evaluate and compare the efficacy of high-flow nasal cannula (HFNC) oxygen therapy versus COT in patients who will undergo prolonged either diagnostic or therapeutic UGI endoscopy in the intensive care unit (ICU) .

Study will be conducted in the intensive care units (ICU) of Ain Shams University Hospitals, Cairo, Egypt. Consented and enrolled seventy patients will be randomly assigned to one of the following two groups:

• Conventional nasal oxygen therapy (COT) group (35 patients): Who will receive 5 L/min oxygen flow through standard nasal cannula (gives FiO2 of about 0.4). The allocated flow rates will be maintained throughout the procedure unless intervention will be required at the discretion of the anesthesiologist in charge of the case.
• High-flow nasal cannula (HFNC) group (35 patients): Who will receive 30 L/min oxygen flow through Vapotherm Precision Flow HFNC. The fraction of inspired Oxygen (FiO2) will be adjusted at 0.4,temperature at 37◦C with 100% humidity
• Upper Gastrointestinal (UGI) Endoscopic and anesthetic care as following:
• Pre-procedural full medical and anesthetic history, clinical examination and revision of routine investigations and radiological images will be done.
• Standard monitoring via GE monitor will be connected to the patient as electrocardiogram (ECG) for heart rate (beats/min), pulse oximetry for (SpO2 as a percentage) and non invasive blood pressure (NIBP) (mmHg).
• The intravenous access (IV) will be assessed and flow will be assured
• After positioning the patient in the left lateral position, he will receive either HFNC or COT.
• All UGI endoscopic procedures will be performed by an accredited gastroenterologist. Anesthetic care will be provided by an accredited specialist anesthesiologist. After confirming the readiness of the endoscopist, all patients will undergo deep sedation under monitored anesthetic care with the use of initial slow intravenous (IV) propofol 0.5-1mg/kg over 3-5 minutes which will be titrated to the desired clinical response.Intermittent boluses of 10-20 mg will be used as maintenance and will also be titrated to the desired sedation level. Both the endoscopist and anesthesiologist will be instructed to provide the usual care except for the participant's assigned oxygen delivery device and rate.
• Interventions to change the oxygen delivery rate, Fio2 or even intubation with invasive mechanical ventilation in response to hypoxia will be at the discretion of the anesthesiologist in charge.
• UGI diagnostic and therapeutic endoscopy will be performed by PentaxR Medical 90k series gastroscopy. Therapeutic gastroscopy will include variceal band ligation, endoscopic hemostasis as injection of bleeding peptic ulcers with adrenaline or bleeders control via either argon plasma coagulation (APC) or heater probe coagulation.
• Patients will continue their monitored care in the medical ICU till the control of the causes of their ICU admission or their end.
• Demographics and medical conditions will be collected from the medical records and anesthesiologist assessments. Oxygenation, anesthetic and procedure-related (intraprocedural and shortly post- procedural) data will be collected also. The collected data results will be revised, electronically recorded in datasheet, coded, tabulated, analyzed, and processed using the proper computerized statistical package program. Suitable statistical analysis will be done according to the type of data obtained for each parameter with comparison between both groups to identify any significant differences between them

Inclusion Criteria:

• Both males and females with age 20-60 years
• American Society of Anesthesiologists (ASA) class I, II or III
• Patients will undergo UGI endoscopic procedure with anticipated procedure time of over 15 minutes because of complexity of the procedure or recurrence, as assessed by the consultant gastroenterologist responsible for the case

Exclusion Criteria:

• Patient refusal or propofol allergy history.
• Suspected difficult airway or Mallampati score more than 3
• Body mass index (BMI) more than 35 kg/m2 (weight will be measured in kilograms and height in meters,then BMI will be measured by equation where: BMI=weight(Kg) / height square (m2))
• Pregnant patients
• Respiratory compromise as patients dependent on supplemental oxygen including respiratory failure or with active chest condition e.g. bronchial asthma or pneumonia
• Cardiovascular compromise including heart failure and shocked patients
• Severe uncontrolled hematemesis with shocked or risk of aspiration.
• Patients deemed as high risk of SRAEs by the anesthesiologist, anticipated requirement or plan for general anesthesia involving airway instrumentation including a laryngeal mask or tracheal intubation.

The statistics methods and results data will be shared after completing the study

The patients and anesthesiologists in charge of the case will be unmasked as High-flow nasal cannula HFNC) shape,setting and preparation are completely different from the Conventional nasal oxygen therapy (COT), so masking both of them is impossible.