High-Flow Nasal Cannula Oxygen Therapy for Carbon Monoxide Poisoning in Dogs: Key Takeaways

Philip R Judge BVSc MVS PG Cert Vet Stud MACVSc (Vet Emergency and Critical Care; Medicine of Dogs)

Introduction

Carbon monoxide (CO) poisoning is a life-threatening emergency we see most commonly in dogs rescued from house fires. While oxygen therapy has always been the mainstay of treatment, this case series from Robertson and colleagues introduces an important advance: the use of high-flow nasal cannula oxygen therapy (HFNOT) to rapidly reduce carboxyhaemoglobin levels. Here are the key clinical takeaways for emergency treatment.

Takeaway 1: HFNOT Achieved Carboxy-haemoglobin Clearance Faster Than Conventional Oxygen Therapy

The three dogs in this series presented with moderate CO poisoning (CO-Hb levels 21.8%, 29.6%, and 27.2%. All were treated with high-flow nasal oxygen therapy at 1 L/kg/min with an FiO₂ of 1.0 for 4-7 hours.

The key outcome:

• CO-Hb half-lives during HFNOT: 79, 86, and 77 minutes respectively
• This is substantially faster than the reported half-life with conventional oxygen therapy:
  • Room air: 4-6 hours
  • Conventional oxygen therapy (FiO₂ 0.4-0.6): ~125 minutes (from prior veterinary literature)
  • Mechanical ventilation (FiO₂ 1.0): 150 minutes (one prior case)

Clinical pearl: While hyperbaric oxygen therapy (the gold standard in human medicine) can achieve half-lives of 15-30 minutes, it’s rarely available in veterinary practice. However, hi-flow nasal oxygen therapy appears to be significantly better than what most of us can deliver with flow-by, mask, or cage oxygen.

Takeaway 2: Patient Factors Can Reduce Efficacy

The physiological advantage of high-flow nasal oxygen therapy  is its ability to deliver warmed, humidified oxygen at high flow rates (up to 60-70 L/min in human medicine; veterinary systems typically used at 1-2 L/kg/min) with an FiO₂ that can be set as high as 1.0.

Why this matters for CO poisoning:

• CO competes with oxygen for haemoglobin binding with 200-250 times greater affinity
• High FiO₂ promotes competitive displacement of CO from haemoglobin
• The higher the FiO₂, the shorter the CO-Hb half-life

However, the delivered FiO₂ may not equal the set FiO₂:

• In healthy dogs, high-flow nasal oxygen therapy  at 1 L/kg/min with set FiO₂ 1.0 delivered intratracheal FiO₂ of 0.95 in non-panting dogs
• In panting dogs, this dropped to 0.67 due to room air admixture
• Tachypnoea, open-mouth breathing, and patient intolerance can all reduce delivered FiO₂

Clinical pearl: Case 2 required flow rate reduction from 1 to 0.6 L/kg/min due to intolerance – but achieved excellent CO-Hb clearance (half-life 86 minutes). If your patient won’t tolerate the ideal settings, some HFNOT is still better than conventional therapy.

Takeaway 3: Anticipate Complications

While all three dogs survived to discharge, their clinical courses highlight the importance of monitoring for complications beyond CO poisoning. One of the cases developed severe hypoxaemia on day 2, despite treatment, as well as gingival ulceration. These complications were attributed to thermal airway and oral cavity injury, and development of non-cardiogenic pulmonary oedema (NCPE). Another of the cases developed aspiration pneumonia, and had initial poor tolerance of the nasal oxygen catheter.

Clinical pearl: CO poisoning is just one component of smoke inhalation injury. These patients can develop NCPE, ARDS, pneumonitis, thermal airway injury, and secondary pneumonia – sometimes days after initial recovery. These cases warrant extended monitoring and cautious discharge planning.

Takeaway 4: Diagnosis Requires CO-Oximetry – Standard Parameters Can Be Misleading

CO poisoning is easy to miss if you rely on routine assessments.

Diagnostic pitfalls:

• PaO₂ remains normal—dissolved oxygen is unaffected, so arterial blood gas alone won’t raise suspicion
• Pulse oximetry is falsely elevated—most machines cannot differentiate oxyhemoglobin from CO-Hb
• Respiratory rate may not increase initially—tissue hypoxia occurs without triggering tachypnoea until acidosis develops

What you need:

• CO-oximetry (blood gas machine that measures CO-Hb directly)
• All three dogs in this series were diagnosed using venous or arterial CO-oximetry

Severity grading (adapted from human medicine):

• Mild: CO-Hb <20%
• Moderate: CO-Hb 20-50%
• Severe: CO-Hb >50%

Clinical pearl: If you have a fire victim patient, don’t wait for respiratory distress to suspect CO poisoning. Run CO-oximetry early. The dogs in this series had levels of 21.8-29.6% – moderate poisoning that warranted aggressive oxygen therapy despite variable increases in respiratory effort.

Takeaway 5: Practical Considerations for High-Flow Nasal Oxygen Therapy in CO-Poisoned Dogs

When to initiate:

• Documented CO-Hb elevation (any level above reference interval in a symptomatic patient)
• Suspected significant exposure even if CO-oximetry unavailable – don’t delay treatment for test results

What settings to use (based on this series):

• Flow rate: Start at 1 L/kg/min
• FiO₂: 1.0 initially
• Temperature: 34-37°C (lower end may improve tolerance)
• Duration: 4-7 hours in this series; guided by repeat CO-oximetry

Monitoring:

• Repeat CO-oximetry at 4-7 hours to document clearance
• Monitor for signs of developing NCPE/ARDS (increased respiratory effort, hypoxemia, lung ultrasound findings of increased numbers of B-lines)
• Be prepared for prolonged oxygen therapy if clinical condition warrants it

When to wean:

• Normalised CO-Hb (<3% in this series)
• Stable respiratory status
• Gradual de-escalation recommended

Limitations to keep in mind:

• Patient tolerance varies
• Panting reduces delivered FiO₂, and sedation improves tolerance

Clinical pearl: The CO-Hb half-lives in this series (77-86 minutes) were longer than those reported in humans on high-flow nasal oxygen therapy  (36.8-48.5 minutes). This likely reflects species differences, panting, and concurrent pulmonary injury – but these still represent significant reductions over standard nasal oxygen therapy.

Summary: A New Tool for a Challenging Toxicity

This case series provides the first evidence that HFNOT is:

• Effective at rapidly reducing CO-Hb in dogs with moderate CO poisoning
• Safe (no complications directly attributed to high-flow nasal oxygen therapy )
• Reasonably well-tolerated with appropriate sedation and flow rate adjustment

While not every practice will have high-flow nasal oxygen therapy  capability, for those that do, it should be strongly considered for CO-poisoned patients. The ability to deliver true high-flow, high-FiO₂ oxygen translates to faster CO clearance, potentially reducing the risk of acute and delayed neurological sequelae.

Key limitations to acknowledge:

• Small case series (n=3)
• No direct comparison to conventional therapy in this study
• Variable clinical courses due to concurrent smoke inhalation injury
• CO-Hb half-life calculations based on limited sampling points

Further research with larger samples is needed to establish optimal protocols and compare high-flow nasal oxygen therapy to other oxygen delivery methods. 

Reference: Robertson L, Coughlin H, Her J. Successful use of high-flow nasal cannula oxygen therapy in three dogs with carbon monoxide poisoning. Journal of Veterinary Emergency and Critical Care. 2026.