Positioning and Flow Effects on Lung Volume in Asymmetric High-Flow Nasal Cannula

Area of Science:

• Respiratory Physiology
• Medical Device Technology

Background:

• High-flow nasal cannula (HFNC) therapy is known to improve oxygenation and increase end-expiratory lung volume (EELV).
• The impact of novel asymmetric cannulas on EELV, particularly concerning body position and breathing route, remains under-explored.

Purpose of the Study:

• To investigate how body position and mouth condition influence EELV during HFNC using asymmetric cannulas.
• To assess the efficacy of different HFNC parameters and patient positions on lung impedance.

Main Methods:

• A prospective, randomized crossover study involving 16 healthy volunteers.
• Measurements of end-expiratory lung impedance (EELI) using electrical impedance tomography (EIT) under various conditions: body positions (Semi-Fowler's, High Fowler's, prone, reverse Trendelenburg), flow rates (40 and 60 L/min), and mouth conditions (open/closed).
• Analysis using a linear mixed-effects model to compare EELI changes from baseline.

Main Results:

• The greatest significant increase in global EELI was observed in the reverse Trendelenburg position at 60 L/min with the mouth closed.
• Mouth closure was identified as a critical factor for enhancing EELI.
• Reverse Trendelenburg position specifically improved EELI in dorsal lung regions at high flow with a closed mouth.

Conclusions:

• Body position, flow rate, and mouth condition significantly affect EELV during asymmetric HFNC therapy.
• The combination of reverse Trendelenburg, high flow (60 L/min), and mouth closure yields the maximal increase in EELV and promotes more homogeneous lung ventilation.
• Encouraging nasal breathing and optimizing patient positioning can enhance the physiological benefits of HFNC.