HFNC and PEEP effect

Q: The continuous positive airway pressure (CPAP) effect, also known as the "PEEP effect" of high-flow nasal cannula oxygenation, is better achieved with? (select one) 

A) mouth close

B) mouth open

Answer: A

Oxygen delivered via high-flow nasal cannulae (HFNC) is gaining popularity in ICUs as it carries many advantages and often prevents invasive intubation. Some of the benefits are:

1. Patient comfort due to small pliable nasal prongs

2. Warming and humidification of secretions

3. Washout of nasopharyngeal dead space 

4. More accurate delivery of oxygen

5. Decreases inspiratory effort 

6. "PEEP effect"

HFNC increases nasopharyngeal airway pressure that peaks at expiration's end, creating the "PEEP effect". This unload auto-PEEP if present, decrease work of breathing (WOB), and enhance oxygenation in patients with alveolar filling pathologies such as congestive heart failure CHF) or the acute respiratory distress syndrome (ARDS). This effect is dose dependent. The best PEEP effect comes when mouth is closed. Every increase of 10 L/minute of flow yields approximately 0.7 cm H2O of airway pressure when the mouth is closed and 0.35 cm H2O when the mouth is open.

#pulmonary

#ventilation

References:

1. Groves N, Tobin A. High flow nasal oxygen generates positive airway pressure in adult volunteers. Aust Crit Care 2007; 20:126.

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

3. Corley A, Caruana LR, Barnett AG, et al. Oxygen delivery through high-flow nasal cannulae increase end-expiratory lung volume and reduce respiratory rate in post-cardiac surgical patients. Br J Anaesth 2011; 107:998.