From the Guidelines
Heated high flow oxygen therapy does not directly cause low CO2 (hypocapnia). In fact, heated high flow nasal cannula (HFNC) therapy typically helps maintain or slightly increase CO2 levels in patients who need respiratory support. HFNC works by delivering warm, humidified oxygen at high flow rates, which creates a small amount of positive pressure in the airways and reduces dead space ventilation. This mechanism actually helps prevent excessive CO2 washout that can occur with other oxygen delivery systems, as noted in a study published in the Annals of Internal Medicine 1. The warming and humidification of the gas prevents airway drying and improves patient comfort, allowing for better tolerance of the therapy. If a patient on HFNC develops low CO2 levels, it's more likely due to their underlying condition causing hyperventilation or other factors rather than the heated high flow therapy itself. In some cases, HFNC may even help normalize CO2 levels in patients with respiratory distress by improving their breathing pattern and reducing work of breathing, as suggested by evidence from a 2021 study on the effectiveness and harms of high-flow nasal oxygen for acute respiratory failure 1.
Some key points to consider when using HFNC therapy include:
- The flow rate of HFNC can be adjusted to meet the individual patient's needs, with flow rates up to 60 L/min possible 1.
- HFNC is well tolerated and may be used as an alternative in hypoxic adult patients requiring medium-concentration to high-concentration oxygen therapy and who are not at risk of hypercapnia, as noted in a 2017 guideline from the British Thoracic Society 1.
- The use of HFNC may help reduce the risk of hypercapnic respiratory failure in patients at risk, although this is not directly related to the effect of HFNC on CO2 levels.
- It is essential to monitor patients on HFNC therapy closely and adjust the flow rate and oxygen concentration as needed to maintain optimal CO2 levels and prevent complications.
Overall, heated high flow oxygen therapy is a safe and effective treatment option for patients with respiratory distress, and it does not directly cause low CO2 levels. However, it is crucial to use this therapy judiciously and monitor patients closely to ensure optimal outcomes, as recommended by recent guidelines and studies 1.
From the Research
Heated High Flow and CO2 Levels
- The relationship between heated high flow oxygen therapy and CO2 levels is complex and not directly addressed in the provided studies 2, 3, 4, 5, 6.
- However, it is known that high flow oxygen therapy can lead to an increase in CO2 levels in some patients, particularly those with chronic obstructive pulmonary disease (COPD) 6.
- The mechanisms leading to oxygen-induced hypercapnia include the abolition of 'hypoxic drive', loss of hypoxic vasoconstriction, and absorption atelectasis leading to an increase in dead-space ventilation and Haldane effect 6.
- There is no direct evidence to suggest that heated high flow oxygen therapy causes low CO2 levels, but rather that it may lead to an increase in CO2 levels in certain patient populations 6.
Patient Populations at Risk
- Patients with COPD, morbid obesity, asthma, cystic fibrosis, chest wall skeletal deformities, bronchiectasis, chest wall deformities, or neuromuscular disorders may be at risk of developing hypercapnia during supplemental oxygen therapy 6.
- The risk of hypercapnia should not be a deterrent to oxygen therapy in hypoxemic patients with chronic lung diseases, as hypoxemia may lead to life-threatening cardiovascular complications 6.