HFNC and gas exchange

 Q: Higher the flow on High Flow Nasal Cannula (HFNC) higher the removal of PCO2? 

A) True

B) False

Answer: B

It is true that HFNC has come as a blessing for physicians and patients as it may mitigate the chances of invasive ventilation and re-intubations. It is now used with high frequency in ICUs. It has a lot of other advantages. It has a lot of other advantages. They are comfortable for patients with soft and pliable nasal prongs. With proper humidification and increased water content in mucous, it facilitates removal of secretion, decreases the work of breathing and so epithelial injury. Another significant advantage of HFNC is some degree of “PEEP/CPAP effect” which also helps in decreasing the work of breathing. To be precise, every increase of 10 L/minute of flow gives about 0.7 cm H2O of airway pressure with closed mouth and 0.35 cm of H2O with open mouth.

One disadvantage of HFNC is decreased CO2 removal. The inspiratory effort is inversely and linearly proportional to the level of the flow rate of oxygen. As the inspiratory effort goes down with higher levels of HFNC, it decreases CO2 removal.

#pulmonary-medicine

References:

1. Rittayamai N, Tscheikuna J, Rujiwit P. High-flow nasal cannula versus conventional oxygen therapy after endotracheal extubation: a randomized crossover physiologic study. Respir Care 2014; 59:485. 

2. Hasani A, Chapman TH, McCool D, et al. Domiciliary humidification improves lung mucociliary clearance in patients with bronchiectasis. Chron Respir Dis 2008; 5:81. 

3.  Parke R, McGuinness S, Eccleston M. Nasal high-flow therapy delivers low level positive airway pressure. Br J Anaesth 2009; 103:886. 

4. Mauri T, Alban L, Turrini C, et al. Optimum support by high-flow nasal cannula in acute hypoxemic respiratory failure: effects of increasing flow rates. Intensive Care Med 2017; 43:1453.