High-flow nasal oxygen therapy reduces work of breathing without altering systemic oxygen delivery or consumption in healthy, anesthetized, spontaneously breathing dogs

Objective: To determine whether high-flow nasal oxygen therapy (HFNOT) reduces esophageal pressure-derived work of breathing (WOB) indices and alters systemic oxygen balance in healthy, anesthetized, spontaneously breathing dogs. Methods: In a prospective, randomized, crossover experimental study, 6 healthy adult Beagles received HFNOT at 0 (control), 1, or 2 L/kg/min (fraction of inspired oxygen, 0.21) under alfaxalone total IV anesthesia, with ≥ 7-day washout periods. Measurements were obtained at baseline and 10, 20, and 30 minutes after flow initiation. Primary outcomes were esophageal pressure swing and esophageal pressure-rate product. Oxygen delivery index, oxygen consumption index, and oxygen extraction ratio were calculated using Fick-derived methods and thermodilution cardiac output. Results: At 2 L/kg/min, esophageal pressure-rate product decreased from 134.9 ± 49.7 cm H2O·breaths/min at baseline to 50.6 ± 21.1 cm H2O·breaths/min, 54.6 ± 22.9 cm H2O·breaths/min, and 48.7 ± 23.8 cm H2O·breaths/min at 10, 20, and 30 minutes after initiation, respectively; esophageal pressure swing decreased from 7.1 ± 2.1 cm H2O to 4.7 ± 1.9 cm H2O at 10 minutes after initiation. The respiratory rate decreased during the 1- and 2-L/kg/min sessions. In contrast, oxygen delivery index, oxygen consumption index, oxygen extraction ratio, arterial oxygen saturation of hemoglobin, and mixed venous oxygen saturation of hemoglobin remained stable across flow conditions and time points. Conclusions: HFNOT at 2 L/kg/min reduced surrogate indices of WOB without altering systemic oxygen delivery or consumption in healthy anesthetized dogs. Clinical Relevance: HFNOT may reduce respiratory effort independently of changes in oxygen metabolism, supporting its physiological safety and potential role in modulating breathing mechanics in veterinary patients.