Failed to reach expected enrollment by anticipated dates.

The aim of this study is to compare two methods of delivery of noninvasive mechanical ventilation (NIV).

Since patient compliance and mechanical characteristics of the delivery devices are two fundamental variables in the success of NIV during acute respiratory failure, our hypothesis is that an improved patient-ventilator interface may improve the efficacy of therapy.

Noninvasive ventilation (NIV) is the delivery of ventilatory support without the need for an invasive artificial airway. The use of noninvasive positive-pressure ventilation (NPPV) in acute respiratory failure has been steadily increasing for intensive care unit (ICU) patients. Noninvasive ventilation can often eliminate the need for intubation or tracheostomy and preserve normal swallowing, speech, and cough mechanisms. Discomfort of the device is one of the reason for the failure of NIV (30-40% of the cases).

The Novastar oro-nasal mask (Dräger Medical, Lubeck, Germany) is a flexible, transparent mask shell with a fine silicone gel cushion which adapts to the wearer's face. The pliable ring embedded inside the flexible clear shell allows the mask to be bent and adjusted to fit the patient's face (customized fit), while minimizing leakages. The mask has magnetic, self aligning clips for capture and secure fastening of the mask headgear. The magnetic clips are self-aligning.

The transparent flexible helmet for NIV (Rüsch 4-Vent, Teleflex Medical Europe, Athlone, Ireland) is fixed with two straps passing through each armpit. The braces are protected by hydrocolloid strips to prevent axillary decubitus. It is important to chose the right size of the helmet to avoid air leakages in the neck region. Two filters in the in- and expiratory way are necessary to reduce noise.

Different devices may lead to varying degrees of discomfort and, thus, improve compliance. Better tolerability of NIV may improve its efficacy. Therefore, we planned this randomized controlled trial to investigate whether different modalities of NIV delivery may affect therapeutical efficacy.

No randomized trials have compared helmets to the NOVASTAR full-face masks. This randomized, controlled study aims to assess whether the new full face mask improves gas exchange in patients admitted to ICU because of acute postoperative respiratory failure.

METHODS

Patients meeting criteria for NIV cycles will be enrolled in this trial. Informed written consent requirements were waived by the Internal Review Board since enrollment criteria meet common clinical guidelines and the two devices are both widely available (and approved for this indication).

Enrollment criteria are:

• Ongoing or recent history of respiratory failure (either primary or secondary)
• PaO2 <60 mmHg if breathing room air or PaO2/FiO2 <300 mmHg if receiving supplemental oxygen
• Acute dyspnea with respiratory rate >25 bpm and accessory muscle recruitment and/or paradoxical abdominal breathing

Patients will be excluded if:

• Refusing NIV
• Comatose (Glasgow Coma Scale <8) or unable to maintain a patent airway
• Hemodynamically unstable (systolic blood pressure <80 mmHg on recruitment, or receiving vasopressors/inotropes; ongoing angina/myocardial infarction; newly-developed arrhythmia with hemodynamic impact)
• Having recently (≤2 weeks) undergone oesophageal or upper respiratory tract surgery

Upon enrolment, patients will be randomized to receive NIV via one of the two available interfaces. In group H (for "helmet"), the continuous positive pressure is obtained by a high influx of fresh gases (air + oxygen) flowing through a high-compliance reservoir, with a positive end-expiratory pressure valve limiting outflow. In the M ("oral-nasal mask") group the same flow scheme is obtained using a T-tube attached to the mask. Patients' heads will be elevated to about 45° in both groups.

In both groups continuous positive airway pressure (CPAP) will be instituted at 5 cmH2O. Pressure will be increased by increments of 2-3 cmH2O until a maximum of 10 cmH2O in order to reach a peripheral blood oxygen saturation (SpO2) ≥ 90% with the lowest FiO2 possible.

Noninvasive ventilation will be ideally maintained for up to 24 h. Patients will be asked to wear the helmet/mask as long as possible. During ventilation-free periods, which will be maintained as short as possible, patients will receive 50% oxygen supplementation. The criteria for success of therapy and discontinuation of NIV will be a reversal of all criteria listed above for enrollment.

Criteria for NIV failure and subsequent intubation and mechanical ventilation will be:

• Coma (Glasgow Coma Scale <8) or inability to maintain a patent airway
• Hemodynamic instability (systolic blood pressure <80 mmHg on recruitment, or receiving vasopressors/inotropes; ongoing angina/myocardial infarction; newly-developed arrhythmia with hemodynamic impact)
• Intolerance to the interface
• Patient's inability to mobilize secretions
• PaO2/FiO2 ratio <140 mmHg after ≥1 h of ventilation

MAIN ENDPOINT AND SAMPLE SIZE

Arterial blood gas analyses will be performed upon enrollment, after 1 h, and after 24 h from enrollment. The null hypothesis of the study is that there will be no difference in the mean PaO2/FiO2 values between the two groups at 24 h. We will consider as clinically and statistically significant a difference of ≥50±60 mmHg between the groups.

A total of 50 patients will be enrolled. Sample size calculations are based on the assumption of a 5% risk of type I error and a 20% risk of type II error, while accounting for a 10-15% attrition rate.

Inclusion Criteria:

• Ongoing or recent history of respiratory failure (either primary or secondary)
• PaO2 <60 mmHg if breathing room air or PaO2/FiO2 <300 mmHg if receiving supplemental oxygen
• Acute dyspnea with respiratory rate >25 bpm and accessory muscle recruitment and/or paradoxical abdominal breathing

Exclusion Criteria:

• Refusing noninvasive ventilation
• Comatose (Glasgow Coma Scale <8) or unable to maintain a patent airway
• Hemodynamically unstable (systolic blood pressure <80 mmHg on recruitment, or receiving vasopressors/inotropes; ongoing angina/myocardial infarction; newly-developed arrhythmia with hemodynamic impact)
• Having recently (≤2 weeks) undergone oesophageal or upper respiratory tract surgery