Study finds HFNOT lowers work of breathing in anesthetized dogs

CURRENT FULL VERSION: A new American Journal of Veterinary Research study adds physiologic evidence for a benefit many clinicians have suspected with high-flow nasal oxygen therapy: it can make breathing easier even when it doesn’t measurably change systemic oxygen transport. Published online April 27, 2026, the randomized crossover experiment found that HFNOT reduced esophageal pressure-derived work-of-breathing indices in healthy, anesthetized, spontaneously breathing dogs, while oxygen delivery and oxygen consumption remained unchanged. (pubmed.ncbi.nlm.nih.gov)

That distinction matters because HFNOT is often discussed primarily as an oxygenation tool. In both human and veterinary medicine, though, the therapy’s proposed mechanisms extend beyond FiO2 support. Reviews of the veterinary literature describe several plausible effects, including nasopharyngeal dead-space washout, delivery of a more consistent inspired gas flow, low-level positive end-expiratory pressure, humidification, and improved tolerance compared with some other oxygen-delivery approaches. Those mechanisms have helped drive growing use in dogs with acute respiratory failure, upper-airway obstruction, carbon monoxide intoxication, and post-extubation support. (frontiersin.org)

In the new study, investigators at Seoul National University, with one co-author affiliated with North Carolina State University, enrolled six healthy adult Beagles in a prospective, randomized, crossover design. Dogs received HFNOT at 0, 1, or 2 L/kg/min with an FiO2 of 0.21 under alfaxalone total IV anesthesia, with washout periods of at least 7 days. The primary endpoints were esophageal pressure swing and esophageal pressure-rate product, both used as surrogate markers of inspiratory effort. At 2 L/kg/min, esophageal pressure-rate product dropped from 134.9 ± 49.7 cm H2O·breaths/min at baseline to roughly 49 to 55 cm H2O·breaths/min across the 10-, 20-, and 30-minute measurements, while esophageal pressure swing fell from 7.1 ± 2.1 cm H2O to 4.7 ± 1.9 cm H2O at 10 minutes. Respiratory rate also decreased during the 1- and 2-L/kg/min sessions. (pubmed.ncbi.nlm.nih.gov)

Just as notable were the variables that did not move. Oxygen delivery index, oxygen consumption index, oxygen extraction ratio, arterial oxygen saturation, and mixed venous oxygen saturation remained stable across flow conditions and time points. In practical terms, that suggests the dogs were not using less oxygen systemically, nor were they receiving more effective whole-body oxygen delivery, despite breathing with less apparent effort. The authors concluded that HFNOT at 2 L/kg/min reduced work of breathing independently of changes in oxygen metabolism, supporting its physiologic safety in this controlled setting. (pubmed.ncbi.nlm.nih.gov)

The study also fits with earlier veterinary work showing that HFNC can improve oxygenation in dogs failing conventional oxygen therapy and is increasingly being used in real-world critical care cases. A 2022 prospective clinical trial in 20 client-owned dogs reported improved hypoxemia with HFNC after failure of conventional oxygen therapy, while recent case reporting has described successful use in dogs with carbon monoxide poisoning. At the same time, published reviews emphasize that complications are usually uncommon but not absent, and tolerance, patient selection, flow settings, and monitoring still matter. (pubmed.ncbi.nlm.nih.gov)

Why it matters: For veterinary professionals, this paper sharpens how HFNOT may be positioned in anesthesia and respiratory support conversations. In healthy anesthetized dogs breathing room air, the benefit was mechanical, not metabolic. That means clinicians shouldn’t assume visible reductions in respiratory effort necessarily reflect improved systemic oxygen delivery, and they shouldn’t use pulse oximetry alone as a proxy for overall cardiopulmonary adequacy. Instead, the findings support HFNOT as a tool that may unload spontaneous breathing, which could be relevant in peri-anesthetic management, recovery, and selected respiratory cases where reducing effort is itself clinically valuable. (pubmed.ncbi.nlm.nih.gov)

There’s also a broader anesthesia context here. A recent Frontiers in Veterinary Science conceptual paper argued that a brief airway-pressure challenge during spontaneous breathing may offer a deliberate, reversible bedside probe of hemodynamic vulnerability to later positive-pressure ventilation in dogs and cats, rather than leaving clinicians to recognize airway-pressure-associated hypotension only after controlled ventilation has already begun. The authors emphasized that any immediate arterial pressure response should be interpreted as an integrated cardiopulmonary stress response—not a simple marker of volume status—and that its meaning may depend on preload sensitivity, right ventricular afterload sensitivity, tricuspid regurgitation, pulmonary vascular burden, anesthetic depth, myocardial reserve, and respiratory mechanics. They also stressed that this is a hypothesis-generating framework, not a validated protocol or ready-to-deploy clinical test, and that any bedside interpretation is context dependent and best suited to settings with continuous, ideally invasive, arterial pressure monitoring. Taken together, that paper and the new AJVR study point toward a more nuanced view of respiratory support in veterinary anesthesia: preserving spontaneous breathing may provide an interpretive window before the circulation is fully exposed to sustained positive-pressure ventilation, and airway pressure, respiratory effort, and hemodynamic tolerance may need to be assessed as related but separate physiologic questions. That synthesis is an inference from the two papers rather than a direct conclusion of either one, but it is a useful framing for clinicians managing marginal patients. (frontiersin.org)

What to watch: The most important next step is clinical translation. This was a six-dog experimental study in healthy Beagles under TIVA, not a trial in dyspneic, hypoxemic, brachycephalic, or cardiovascularly unstable patients. Future work will need to test whether lower work of breathing with HFNOT leads to better tolerance, fewer intubations, smoother recoveries, or improved outcomes in actual hospital patients, and to define which flow settings and case types benefit most. In parallel, the proposed airway-pressure challenge framework will need technical standardization and prospective validation before it can be treated as a clinical test or algorithm for deciding how safely a given patient will tolerate positive-pressure ventilation. (pubmed.ncbi.nlm.nih.gov)