Patients suffering from pathology of posterior eye chamber such as diabetic retinopathy, retinal detachment, traumatic eye injury, retained lens fragments, macular hole, pucker, dislocated intraocular lens after cataract surgery or vitreomacular traction are often subjected to pars plana vitrectomy (PPV). PPV is minimally invasive endo-microscopic operation usually performed in topical anesthesia combined with sub-Tenon or retrobulbar block done by surgeon, supplemented by intravenous analgo-sedation given by anesthesiologist.

Continuous infusion and dose adjustment of intravenous anesthetics applied should procure moderate sedation and preservation of patients' spontaneous ventilation. However, despite carefully applied anesthetics and standard low-flow nasal oxygenation (LFNO) (5 L/min O2 via nasal catheter), inadequate spontaneous breathing can occur leading to low blood oxygen level (hypoxia). Obese patients are susceptible to hypoxia and hypercapnia (high CO2 blood level) during analgo-sedation. Respiratory instability of obese patients is often associated to their subsequent circulatory instability (heart rate and blood pressure disorders).

On the other hand, high-flow nasal oxygenation (HFNO) is usually used during anesthesia induction when difficult maintenance of airway patency is expected, in intensive care units during weaning patients from mechanical respirator and in postanesthesia care units during awakening from anesthesia. It can deliver 20 to 70 L/min, up to 100% inspiratory fraction of O2 (FiO2) to patient. High oxygen/air flow produces 3-7 cmH2O of continuous pressure in patients' upper airways therefore providing better oxygenation. Oxygen/air mixture delivered by HFNO is humidified and heated, thus more comfortable to patient than dry and cold LFNO.

Aim of this study is to compare effect of HFNO to LFNO during intravenously applied standardized analgo-sedation given for PPV in obese adult patients.

Investigators hypothesize that obese patients, whose breathing pattern is preserved, receiving HFNO vs. LFNO during standardized analgo-sedation for PPV will be more respiratory and circulatory stable, preserving normal blood O2 and CO2 level, breathing pattern, heart rate and blood pressure.

Patients suffering from pathology of posterior eye chamber such as diabetic retinopathy, retinal detachment, traumatic eye injury, retained lens fragments, macular hole, pucker, dislocated intraocular lens after cataract surgery or vitreomacular traction are often subjected to pars plana vitrectomy (PPV).

PPV is minimally invasive micro-endoscopic surgery of posterior eye chamber. Patients usually receive analgo-sedation combined with topical anesthesia, which, depending on the type of surgery, precedes a regional, retrobulbar or sub-Tenon block. Although lower doses of intravenous anesthetics are carefully titrated in continuous infusion and standard, low - flow nasal oxygenation (LFNO) is applied, patients are prone to respiratory insufficiency. Obese patients are especially susceptible to bradypnoea, transitory apnoea, hypoxia and hypercapnia. Respiratory instability is then often followed by circulatory one presented by heart rate and blood pressure deflections from baseline values. It is known that higher anesthesia risk obese patients may suffer from serious complications due to respiratory issues during analgo-sedation, even fatal outcome may occur.

LFNO is applied at rate of 5 L/min O2 per nasal catheter, reaching inspiratory fraction of oxygen (FiO2) of 40%. High-flow nasal oxygenation (HFNO) is an innovative method of patient oxygenation that delivers warmed and moistened oxygen and air mixture with a flow rate of up to 70 L/min and up to 100% FiO2 via specially designed soft nasal cannula. It is known that 40 L/min of oxygen/air mixture delivered by HFNO provides 40% FiO2 applying continuous positive inspiratory pressure of 3-7 cmH2O which ensures continuous non-invasive support of patients' spontaneous ventilation and thus better oxygenation stability of the patient.

OBJECTIVE: The study aims to determine the effect of HFNO versus LFNO on the stability of spontaneous ventilation during standardized intravenous analgo-sedation for PPV in normal weight and obese patients.

HYPOTHESIS: Investigators hypothesize that administration of HFNO in comparison with LFNO in patients with preserved spontaneous breathing during the standard analgo-sedation procedure will contribute to better oxygenation maintenance and, consequently, greater peri-procedural safety of patients, especially in obese patients.

Investigators expect that HFNO will provide reduced bradypnoea intervals (bradypnoea <12 breaths/min, FoB 1/min), longer maintenance of adequate oxygenation, shorter intervals of desaturation (peripheral blood oxygen saturation - SpO2≤92%), reducing hypercapnia (expiratory carbon-dioxide - expCO2≥45 mmHg) and less airway opening maneuvers performed by attending anesthesiologist (AOM). These will prevent partial respiratory insufficiency detected by low SpO2 accompanied by low or normal expiratory carbon-dioxide level (expCO2), and global respiratory insufficiency detected by decreased SpO2≤92% and increased expCO2≥45 mmHg.

Investigators plan to conduct prospective, parallel group, randomized controlled clinical trial. Trial will be managed according to principles of Declaration of Helsinki for scientific clinical research and will be planned and guided according to CONSORT guidelines (Consolidated Standards of Reporting Trials). The trial has been approved by Hospital's Ethic Committee.

The source of information are going to be 126 adult patients scheduled for PPV under analgo-sedation. Eligible participants will be interviewed and examined ambulatory by anesthesiologist, their ASA status, difficulty of airway management and body mass index (BMI) evaluated. After initial examination inclusive and exclusive criteria will be distinguished. Eligible participants who give voluntarily their written consent of participation will be included in this study. After that, participants will be assigned to equal normal weight (18\

Inclusion Criteria:

• Normal weight and obese patients (18\

Anesthesiologist who interviews and examines patients scheduled for PPV under analgo-sedation will enroll eligible participants and offer procedure explanation with possibility to sign uniformed written consent. Unique personal hospital admission number (UPHAN) will be assigned to all eligible participants. Participants will be randomized to control or intervention group by using random numbers generator. Anesthesiologist who implements anesthesia will receive nontransparent envelope with assigned intervention provided by independent investigator and will not decide which participant will receive LFNO or HFNO. However, attending anesthesiologist and participants will unavoidably be aware of type of oxygenation applied. Collected data are objective measures. Investigator who collects data after procedure will be unaware of study protocol and will enter data to formatted database. Participants' data will be noted under UPHAN. Outcome assessors will be unaware of intervention applied.