High-flow Nasal Cannula vs. Helmet PSV vs. Helmet CPAP During Respiratory Failure

Study Overview
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Brief Summary
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The investigators designed a cross-over, randomized trial to assess the physiological effects of helmet pressure support ventilation (PSV) and continuous positive airway pressure (CPAP) as compared to high-flow nasal cannula during the early phase of acute hypoxemic respiratory failure

Detailed Description
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Setting: 21-bed general ICU, emergency room of the Emergency department (ED), Fondazione Policlinico Universitario Agostino Gemelli IRCCS, Rome, Italy.. Patients: adult hypoxemic non-hypercapnic patients admitted to the emergency department or the ICU with de novo acute respiratory failure will be assessed for the enrolment. Each eligible patient, in the absence of exclusion criteria, will receive 15 minutes of heated and humidified 60% oxygen at a rate of 50 l/min via a non-rebreathing face mask. An ABG will be then collected and PaO2/FiO2 ratio computed: given the high flows used, actual FiO2 will be approximated to the set one. Nonhypercapnic patients with a PaO2/FiO2≤200 mmHg will be enrolled. In the absence of exclusion criteria and if all other inclusion in criteria are met, patients showing PaO2/FiO2≤300 and >200 mmHg will be treated according to the clinical practice eventually reassessed for the presence of oxygenation criterion subsequently. Enrolled patients will receive all the interventions (helmet CPAP, PSV and high-flow nasal cannula) in a randomized, cross-over fashion, for 40 minutes each. At the end of the study, the patient will receive the treatment that will be shown as more appropriate for the patient, according to the attending physician, who will be informed about the results of the study on the individual patient.

Official Title
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Physiological Comparison of High-flow Nasal Cannula, Helmet Pressure Support Ventilation and Continuous Positive Airway Pressure During Acute Hypoxemic Respiratory Failure: a Randomized Cross-over Study

Conditions
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Respiratory Failure, Hypoxemia

Intervention / Treatment
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* Other: Respiratory support (High-flow oxygen therapy)
* Other: Respiratory support (Helmet PSV)
* Other: Respiratory support (Helmet CPAP)


Participation Criteria
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Eligibility Criteria
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Inclusion Criteria: Patients: adult hypoxemic non-hypercapnic patients admitted to the emergency department or the ICU with de novo acute respiratory failure will be assessed for the enrolment. Patients will be considered eligible whether all the following inclusion criteria are met: Respiratory rate>25 bpm. PaO2/FiO2 ≤200 in the supine position, measured after 15 minutes of high flow treatment with face mask (60 l/min, temperature of the humidification chamber set at 37°C, FiO2 set to achieve a SpO2 >92% and <98%). Given the use of the high flows, nominal FiO2 will be considered a reliable estimate of the actual one. PaCO2 <45mmHg Absence of history of chronic respiratory failure or moderate to severe cardiac insufficiency. Written informed consent Exclusion Criteria: Exacerbation of asthma or chronic obstructive pulmonary disease; Cardiogenic pulmonary oedema; Haemodynamic instability (Systolic blood pressure <90 mmHg or mean arterial pressure <65 mmHg) and/or lactic acidosis (lactate >5 mmol/L) and/or clinically diagnosed Shock Metabolic Acidosis (pH <7.30 with normal- or hypo-carbia); Glasgow coma scale <13; Recent head surgery or anatomy that prevent the application of helmet or nasal cannula to patient's face.

Ages Eligible for Study
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Minimum Age: 18 Years

Sexes Eligible for Study
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All

Accepts Healthy Volunteers
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No

Study Plan
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How is the study designed?
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Design Details

Primary Purpose: Treatment
Allocation: Randomized
Intervention Model: Crossover Assignment
Masking: None (Open Label)


Arms and Interventions

| Participant Group/Arm | Intervention/Treatment |
| --- | --- |
| Experimental: High-flow oxygen therapy<br>Nasal high flow oxygen therapy will be delivered with the Optiflow system. Initial set flow will be ≥ 50 /min and flows will be decreased in case of intolerance and/or according to patients' requirements: flows≥30 L/min will be mandatory in all enrolled patients. Humidification chamber (MR860, Fisher and Paykel healthcare, New Zealand) will be set at 37 °C or 34 °C according to patient's comfort33. FiO2 will be titrated to obtain an SpO2≥92% and ≤98%. | Other: Respiratory support (High-flow oxygen therapy)<br>* Noninvasive respiratory support respiratory support<br>|
| Experimental: Helmet PSV<br>Dedicated helmets for noninvasive ventilation will be used and size will be chosen according to neck circumference or according to manufacturer recommendations. Each patient will be connected to a compressed-gas based ventilator through a bitube circuit with no humidification. The ventilator will be set in PSV, with the following suggested settings 34-38: initial pressure support≥8-10 cmH2O and adequate to permit of a peak in the inspiratory flow of 100 l/min; positive end-expiratory pressure=10-12 cmH2O and increased to achieve the oxygenation target according to the choice of the attending physician. FiO2 will be titrated to obtain an SpO2≥92% and ≤98%. Inspiratory flow trigger = 1 l/min or according to the practice of each institution; fastest pressurization time; expiratory trigger: 10-50% of the maximum inspiratory flow; maximum inspiratory time 1.2 second. | Other: Respiratory support (Helmet PSV)<br>* Noninvasive respiratory support respiratory support<br>|
| Experimental: Helmet CPAP<br>Dedicated helmets for noninvasive ventilation will be uses and size will be chosen according to neck circumference or according to manufacturer recommendations. Treatment will be delivered through a high-flow generator. The following settings will be applied: Continuous air flow=50-60 L/min. Expiratory positive end-expiratory pressure valve set to achieve a PEEP==10-12 cmH2O and eventually increased to achieve the oxygenation target according to the choice of the attending physician. FiO2 will be titrated to obtain an SpO2≥92% and ≤98%. Pressure inside the helmet will be monitored with a manometer in order to maintain the set PEEP. | Other: Respiratory support (Helmet CPAP)<br>* Noninvasive respiratory support respiratory support<br>|

What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Inspiratory effort | The negative deflection in esophageal pressure during inspiration | 40 minutes | 
| Tidal volume | The tidal change in lung impedance, assessed by electrical impedance tomography | 40 minutes | 

Secondary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Oxygenation | Ratio of PaO2 to FiO2 | 40 minutes | 
| Tidal volume distribution | Distribution of tidal volume within the lung regions, assessed by electrical impedance tomography | 40 minutes | 
| Carbon dioxide | Blood carbon dioxide, measured with the arterial blood gas analysis | 40 minutes | 
| Respiratory rate | Respiratory rate/minute, assessed with the esophageal pressure | 40 minutes | 
| Dyspnea | Dyspnea assessed with the visual analog scale, 0-10 scale where the highest value corresponds to the highest degree of dyspnea | 40 minutes | 
| Comfort | Comfort assessed with the visual analog scale, 0-10 scale where the highest value corresponds to the highest degree of discomfort | 40 minutes | 
| Global impedance-derived End-expiratory lung volume | End-expiratory lung volume, measured with electrical impedance tomography | 40 minutes | 
| Regional impedance-derived End-expiratory lung volume | End-expiratory lung impedance in the four regions of the lungs (ventral, mid-ventral, mid-dorsal, dorsal), measured with electrical impedance tomography | 40 minutes | 
| Dynamic transpulmonary driving pressure | The tidal change in transpulmonary pressure | 40 minutes | 
| Global impedance-derived lung dynamic strain | Change in impedance due to tidal volume / end expiratory lung impedance, both measured with electrical impedance tomography | 40 minutes | 
| Regional impedance-derived lung dynamic strain | Change in impedance due to tidal volume / end expiratory lung impedance in the four regions of the lungs (ventral, mid-ventral, mid-dorsal, dorsal), measured with electrical impedance tomography | 40 minutes | 
| Respiratory system dynamic compliance | Ratio of the tidal change in lung impedance to dynamic transpulmonary driving pressure | 40 minutes | 
| Pendelluft | Occurrence of intra-tidal shift of gas within different lung regions at beginning of inspiration | 40 minutes | 
| Work of breathing | Esophageal pressure simplified pressure time product per minute | 40 minutes |