Differential impact of flow and mouth leak on oropharyngeal humidification during high-flow nasal cannula: a neonatal bench study

The effects of flow settings during high-flow nasal cannula oxygen therapy for neonates and young children

BACKGROUND

During neonatal and paediatric high-flow nasal cannula therapy, optimising the flow setting is crucial for favourable physiological and clinical outcomes. However, considerable variability exists in clinical practice regarding initial flows and subsequent adjustments for these patients. Our review aimed to summarise the impact of various flows during high-flow nasal cannula treatment in neonates and children.

METHODS

Two investigators independently searched PubMed, Embase, Web of Science, Scopus and Cochrane for in vitro and in vivo studies published in English before 30 April 2023. Studies enrolling adults (≥18 years) or those using a single flow setting were excluded. Data extraction and risk of bias assessments were performed independently by two investigators. The study protocol was prospectively registered with PROSPERO (CRD42022345419).

RESULTS

38 406 studies were identified, with 44 included. In vitro studies explored flow settings' effects on airway pressures, humidity and carbon dioxide clearance; all were flow-dependent. Observational clinical studies consistently reported that higher flows led to increased pharyngeal pressure and potentially increased intrathoracic airway pressure (especially among neonates), improved oxygenation, and reduced respiratory rate and work of breathing up to a certain threshold. Three randomised controlled trials found no significant differences in treatment failure among different flow settings. Flow impacts exhibited significant heterogeneity among different patients.

CONCLUSION

Individualising flow settings in neonates and young children requires consideration of the patient's peak inspiratory flow, respiratory rate, heart rate, tolerance, work of breathing and lung aeration for optimal care.

Comparison of actual performance in humidification among different high-flow nasal cannula devices: a bench study

Background

The physiological effects of HFNC devices are closely related to temperature and humidity. HFNC devices from different manufacturers may have varied performances. It is unclear whether there are differences in the humidification performance of different HFNC devices and the degree of differences.

Methods

Four integrated HFNC devices (AIRVO 2, Fisher & Paykel Healthcare, Auckland, New Zealand; TNI softFlow 50, TNI Medical AG, Würzburg, Germany; HUMID-BH, RESPIRACARE, Shenyang, China; OH-70C, Micomme, Hunan, China) and a ventilator with an HFNC module (bellavista 1000, Imtmedical, Buchs, Switzerland) were evaluated using their matching circuits. The dew point temperature was set at 31, 34, and 37°C (set-DP). In MR850, it was set to non-invasive mode (34°C/-3°C) and invasive mode (40°C/-3°C), respectively. At each level of set-DP, the flow was set from 20 L/min up to its maximum set limit at a gradient of 5 L/min or 10 L/min. After stabilization, the dew point temperature, temperature, relative humidity, and flow rate of the delivered gas from the cannulas were recorded.

Results

There were significant differences in actual-DP among these devices at any set-DP (p < 0.001). The actual-DP of OH-70C and TNI softFlow 50 was lower than set-DP, and the difference between the actual-DP and the set-DP of these two devices increased with the increase of set-DP. AIRVO 2, bellavista 1000 (MR850), and HUMID-BH can provide the nominal humidity at 37°C. The actual-DP increased with the increase of set-flow under each set-DP in AIRVO 2, TNI softFlow 50 and bellavista 1000 (MR850), but decreased when the set-flow was greater than 60 L/min. The actual-T of the delivered gas was higher than actual-DP in all devices and was higher than set-DP in AIRVO 2 and HUMID-BH.

Conclusion

Set-flow, set-DP, and types of devices will affect the actual temperature and humidity of the delivered gas. AIRVO 2, bellavista 1000 (MR850), and HUMID-BH can provide the nominal humidity at 37°C and may be more suitable for tracheotomy patients. The flow rate over 60 L/min should be set with caution.

Carbon dioxide diffusion coefficient in noninvasive high-frequency oscillatory ventilation

OBJECTIVES

The carbon dioxide (CO₂ ) diffusion coefficient (DCO ₂ ) reflects CO ₂ removal during high-frequency oscillatory ventilation (HFOV). We hypothesized that despite leak flow during noninvasive HFOV (nHFOV) DCO ₂ continues to indicate ventilation efficacy.

METHODS

A neonatal airway model including CO₂ production and an adjustable oropharyngeal leak was connected to a ventilator via bi-nasal prongs. Pressures and gas flows were measured at prongs, trachea, and leak. Oscillatory tidal volumes below (V _{T trachea} ) and above the leak (V _{T prong} ) were calculated from tracheal and leak flows. DCO ₂ was calculated using V _{T trachea} (DCO _{2 trachea} ) and V _{T prong} (DCO _{2 prong} ) and compared with CO ₂ partial pressure (pCO ₂ ). Effects of leak flow (0, 5, or 10 L/min) on DCO ₂ were assessed at fixed pressure amplitudes or predefined oscillatory volumes under steady-state pCO ₂ conditions in the modeled lung.

RESULTS

DCO_{2 trachea} correlated strongly with pCO ₂ , independent of the leak flow level (P < 0.0001). DCO _{2 prong} correlated with pCO ₂ without and with moderate leak (P < 0.0001) but not with maximum leak (P = 0.1432). V _{T trachea} correlated with the quotient of tracheal pressure amplitude and frequency irrespective of the leak (P < 0.0001). Based on the pressure amplitude at prong level (A _prong ) V _{T trachea} continued to follow a linear model of which the slopes decreased with increasing leak flow. V _{T prong} correlated with the quotient of A _prong and frequency, irrespective of the leak (P < 0.0001).

CONCLUSIONS

DCO₂ obtained at the airway opening at prong level reflects ventilation efficacy during nHFOV even in the presence of moderate oropharyngeal leak.