Asymmetrical High Flow Nasal Cannula and End-Expiratory Lung Impedance

Objective: The primary aim is to assess end-expiratory lung impedance (EELI) changes during the application of high-flow oxygen therapy using asymmetric nasal cannulae, comparing conditions with the mouth closed and open in healthy volunteers in various positions. The secondary objective includes evaluating respiratory rate, shortening fraction, and diaphragm excursion via ultrasound.

Study Design: This is a prospective observational cohort study conducted in the Critical Care Unit of Sanatorio Parque Rosario from November 5 to December 31, 2024. It will involve 20 healthy adult volunteers without respiratory conditions, with informed consent obtained from all participants. Volunteers with contraindications for electrical impedance tomography (EIT) will be excluded.

Methods: Equipment Used: PulmoVista 500 Dräger (EIT), AIRVO 2 (high-flow oxygen generator), asymmetric nasal cannula (Optiflow OPT 966), Toshiba iStyle ultrasound machine.

Procedures: The study includes EELI measurements in different positions (semi-seated, supine Fowler, prone, and prone Fowler) with various high-flow oxygen settings (40 and 60 L/min). Diaphragm excursion and thickening will be assessed using ultrasound.

Scenarios and Measurements: 17 different testing scenarios will be conducted, with 16 intervals for washout breathing at room air between scenarios. Data on EELI, respiratory rate, and diaphragm measurements will be collected.

Methodology:

Procedures: EELI, respiratory rate, and diaphragm measurements will be taken in various body positions while using high-flow oxygen therapy (HFNC) set at 40 and 60 L/min. Diaphragm excursion and thickening will be evaluated with ultrasound.

Data Collection and Analysis: Volunteers will participate in 17 different testing scenarios, with intervals of 5-minute washout periods breathing room air in a semi-seated position between each measurement. Continuous variables will be expressed as mean ± standard deviation or median and interquartile range. Repeated measures ANOVA will be used for statistical comparisons, with significance set at p \< 0.05.

17 Testing Scenarios:

Semi-seated at 45° breathing room air. Semi-seated at 45° with asymmetric HFNC at 40 L/min, mouth closed for 5 minutes.

Semi-seated at 45° with asymmetric HFNC at 40 L/min, mouth open for 5 minutes. Semi-seated at 45° with asymmetric HFNC at 60 L/min, mouth closed for 5 minutes.

Semi-seated at 45° with asymmetric HFNC at 60 L/min, mouth open for 5 minutes. Supine in Fowler position (60°) with asymmetric HFNC at 40 L/min, mouth open for 5 minutes.

Supine in Fowler position (60°) with asymmetric HFNC at 40 L/min, mouth closed for 5 minutes.

Supine in Fowler position (60°) with asymmetric HFNC at 60 L/min, mouth open for 5 minutes.

Supine in Fowler position (60°) with asymmetric HFNC at 60 L/min, mouth closed for 5 minutes.

Prone at 180° with asymmetric HFNC at 40 L/min, mouth open for 5 minutes. Prone at 180° with asymmetric HFNC at 40 L/min, mouth closed for 5 minutes. Prone at 180° with asymmetric HFNC at 60 L/min, mouth open for 5 minutes. Prone at 180° with asymmetric HFNC at 60 L/min, mouth closed for 5 minutes. Prone Fowler position with asymmetric HFNC at 40 L/min, mouth open for 5 minutes.

Prone Fowler position with asymmetric HFNC at 40 L/min, mouth closed for 5 minutes.

Prone Fowler position with asymmetric HFNC at 60 L/min, mouth open for 5 minutes.

Prone Fowler position with asymmetric HFNC at 60 L/min, mouth closed for 5 minutes.

Duration per Participant: Approximately 2 hours and 15 minutes.

Ethical Considerations: All data will be anonymized and kept confidential. Participants' rights to withdraw at any time will be respected, and no personal identifying information will be disclosed.

This comprehensive approach aims to elucidate the physiological impacts of using asymmetric HFOT on end-expiratory lung volume and related respiratory parameters in various positions and conditions.

Eligibility Criteria:
Inclusion Criteria:

* healthy volunteers between 18 and 50 years of age who sign the informed consent form, without respiratory pathology.

Exclusion Criteria:

* contraindication to implement electrical impedance tomography or high flow oxygen therapy