A high-flow nasal cannula system with relatively low flow effectively washes out CO2 from the anatomical dead space in a sophisticated respiratory model made by a 3D printer

Yu Onodera; Ryo Akimoto; Hiroto Suzuki; Masayuki Okada; Masaki Nakane; Kaneyuki Kawamae

doi:10.1186/s40635-018-0172-7

A high-flow nasal cannula system with relatively low flow effectively washes out CO₂ from the anatomical dead space in a sophisticated respiratory model made by a 3D printer

Intensive Care Med Exp. 2018 Mar 15;6(1):7. doi: 10.1186/s40635-018-0172-7.

Authors

Yu Onodera¹, Ryo Akimoto², Hiroto Suzuki², Masayuki Okada², Masaki Nakane², Kaneyuki Kawamae²

Affiliations

¹ Department of Anesthesiology, Faculty of Medicine, Yamagata University, 2-2-2 Iidanishi, Yamagata City, Yamagata Prefecture, 990-9585, Japan. yu1983624@yahoo.co.jp.
² Department of Anesthesiology, Faculty of Medicine, Yamagata University, 2-2-2 Iidanishi, Yamagata City, Yamagata Prefecture, 990-9585, Japan.

Abstract

Background: Although clinical studies of the high-flow nasal cannula (HFNC) and its effect on positive end-expiratory pressure (PEEP) have been done, the washout effect has not been well evaluated. Therefore, we made an experimental respiratory model to evaluate the respiratory physiological effect of HFNC.

Methods: An airway model was made by a 3D printer using the craniocervical 3D-CT data of a healthy 32-year-old male. CO₂ was infused into four respiratory lung models (normal-lung, open- and closed-mouth models; restrictive- and obstructive-lung, open-mouth models) to maintain the partial pressure of end-tidal CO₂ (P_ETCO₂) at 40 mmHg. HFNC flow was changed from 10 to 60 L/min. Capnograms were recorded at the upper pharynx, oral cavity, subglottic, and inlet sites of each lung model.

Results: With the normal-lung, open-mouth model, 10 L/min of HFNC flow decreased the subglottic P_ETCO₂ to 30 mmHg. Increasing the HFNC flow did not further decrease the subglottic P_ETCO₂. With the normal-lung, closed-mouth model, HFNC flow of 40 L/min was required to decrease the P_ETCO₂ at all sites. Subglottic P_ETCO₂ reached 30 mmHg with an HFNC flow of 60 L/min. In the obstructive-lung, open-mouth model, P_ETCO₂ at all sites had the same trend as in the normal-lung, open-mouth model. In the restrictive-lung, open-mouth model, 20 L/min of HFNC flow decreased the subglottic P_ETCO₂ to 25 mmHg, and it did not decrease further. As HFNC flow was increased, PEEP up to 7 cmH₂O was gradually generated in the open-mouth models and up to 17 cmH₂O in the normal-lung, closed-mouth model.

Conclusions: The washout effect of the HFNC was effective with relatively low flow in the open-mouth models. The closed-mouth model needed more flow to generate a washout effect. Therefore, HFNC flow should be considered based on the need for the washout effect or PEEP.

Keywords: High-flow nasal cannula; PEEP; Rebreathing; Ventilation; Washout effect; Work of breathing.