High-Flow Nasal Oxygenation Is Associated with Improved Respiratory Stability During Moderate Multimodal...

Background/Objectives: High-flow nasal oxygenation (HFNO) may improve respiratory stability during procedural sedation, but treatment-associated differences across patient risk categories remain uncertain. We compared HFNO with low-flow nasal oxygenation (LFNO) during moderate multimodal analgosedation (MMAS) for pars plana vitrectomy (PPV) in patients with ASA physical status I-III. Methods: In this prospective, single-center randomized trial, 164 adults undergoing elective PPV under regional eye anesthesia with MMAS were randomized to HFNO (40 L·min^-1, set FiO₂ 0.40) or LFNO (5 L·min^-1, intended to approximate a nominal FiO₂ of 0.40). Sedation depth was monitored using the Patient State Index and evaluated using the Ramsay Sedation Scale. The primary outcome was maintenance of target oxygenation (SpO₂ 94-98%) without hypoxemia (SpO₂ < 90%), assessed by peripheral oxygen saturation (SpO₂) at three predefined time points (T0, T1, and T2). Secondary outcomes included breathing frequency (BF), measured end-tidal CO₂ (EtCO₂), and clinically significant bradypnea (CSB), defined as ≥1 bradypnea episode (BF < 12 breaths·min^-1 persisting ≥1 min) accompanied by SpO₂ 90-93%, EtCO₂ > 45 mmHg, or both. Results: The primary outcome showed no between-group difference. No hypoxemia (SpO₂ < 90%) occurred. Oxygenation below the target range (SpO₂ 90-93%) was less frequent with HFNO peri-procedurally (adjusted RR, 0.14; 95% CI, 0.03-0.56; p = 0.006) and post-procedurally (adjusted RR, 0.15; 95% CI, 0.04-0.64; p = 0.010). Significant treatment × ASA interactions were observed for BF and measured EtCO₂ peri-procedurally. In exploratory ASA-stratified analyses, ASA III patients receiving HFNO had higher BF, fewer CSB episodes, and lower measured EtCO₂ than those receiving LFNO. Conclusions: HFNO was associated with improved respiratory stability compared with LFNO, with treatment-associated differences varying across ASA strata.