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

Abstract

BackgroundAlthough 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.MethodsAn 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 (PETCO2) 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.ResultsWith the normal-lung, open-mouth model, 10 L/min of HFNC flow decreased the subglottic PETCO2 to 30 mmHg. Increasing the HFNC flow did not further decrease the subglottic PETCO2. With the normal-lung, closed-mouth model, HFNC flow of 40 L/min was required to decrease the PETCO2 at all sites. Subglottic PETCO2 reached 30 mmHg with an HFNC flow of 60 L/min. In the obstructive-lung, open-mouth model, PETCO2 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 PETCO2 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.ConclusionsThe 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.

Physiologic Effects of High-Flow Nasal Cannula in Healthy Subjects

“…Analysis of our data, therefore, suggested that the reduction of _ V E observed at 40 and 60 L/min, associated with stable V A (ie, stable capillary P CO 2 ), is the in vivo expression of a reduction in dead-space ventilation related to a major decrease in breathing frequency and a washout of the anatomic dead space. This observation was in line with previous data obtained on the bench with upper-airway models, 26,40 which demonstrated that HFNC was capable of effectively washing out the upper airways and thus reducing CO 2 rebreathing with relatively low flows. As a result of this dead-space washout, HFNC with flow that ranged from 20 to 40 L/min may reduce P CO 2 in the clinical setting, as recently evidenced by Bräunlich et al 19 in stable subjects with COPD.…”

“…Nevertheless, it has recently been shown that endtidal P CO 2 could be reduced up to 30 mm Hg when applying HFNC at 60 L/min to an experimental model that simulates normal lung with a closed mouth. 40 Such a reduction of P CO 2 , even transient, and, if confirmed in further studies, could explain both the absence of improvement in WOB and the increase in inspiratory resistance (accompanied by an increase in DP es ) observed in our subjects, as previously described by Jounieaux et al 42 in healthy subjects who were undergoing nasal intermittent positive-pressure ventilation. Another explanation for the absence of improvement in respiratory effort with HFNC in this population of healthy subjects was the baseline values, which were already low, in line with what is described in the literature 35,43 and, therefore, subject to minimal improvement despite significant reduction in dead-space ventilation.…”

“…It has been repeatedly demonstrated in upper airway models that HFNC is capable of effectively washing out the upper airways and thus reducing CO 2 rebreathing with relatively low flows. 26,40 The baseline hypothesis of our study was that a reduction in dead-space ventilation, if confirmed, could lead to a reduction of the respiratory drive and the WOB in healthy awake subjects. We failed to demonstrate any reduction in respiratory effort in the present study, even though this phenomenon has previously been reported in subjects with various severity of respiratory failure.…”

The impact of high-flow nasal cannula oxygen therapy on exercise capacity in fibrotic interstitial lung disease: a proof-of-concept randomized controlled crossover trial

“…Conversely, we found that HFNC was inferior to VM in a few patients (Case 6, 7, 9). A recent experimental study using an airway model made with a 3D printer demonstrated that increasing the flow rate of HFNC generates higher positive end-expiratory pressure (PEEP) but does not necessarily increase the washout effects [25]. In our study, two patients complained about nasal pain, although it improved immediately.…”

High-Flow Nasal Cannula Versus Standard Oxygen Therapy After Extubation in Liver Transplantation: A Matched Controlled Study

“…In fact, the literature reports reduced anatomic dead space due to increased nasopharyngeal washout, with a consequently larger fraction of minute ventilation participating in gas exchange. 35 Frequently, candidates for liver transplantation display a restricted respiratory pattern related to the size of the ascites and/or pleural effusion. 36 In fact, in our population, we detected a significantly low preoperative P aCO 2 , especially those in the standard O 2 group who had more ascites.…”