Non-Invasive Mechanical Ventilation Versus Oxygen Therapy in Patients With Acute Respiratory Failure After Extubation in a Intensive Care Unit

Patients. Medical and surgical patients admitted to intensive care unit with 18 years of age or older in weaning from their first episode of mechanical ventilation for more than 24 hours were included. Patients with structural neurological disorder, acute toxic-metabolic neurological encephalopathy with neurological deficit [estimated by a Glasgow Coma Score <14 points] at the time of weaning, neuromuscular disease, chronic obstructive pulmonary disease receiving non-invasive ventilation, limitation of life support therapy during their admission, tracheostomized patients, spinal cord injuries, scheduled surgical procedure during the 48 hours following extubation, intensive care unit readmission, transfer to another centre or a contraindication to non-invasive ventilation were excluded.

Weaning protocol. The beginning of weaning was considered when patients were conscious, without pain, connected to mechanical ventilation in pressure support ventilation mode, fraction of inspired oxygen ≤0.5, positive end-expiratory pressure +5cmH20, dopamine ≤5 mcgr/kg/min or noradrenaline ≤0.2 mcgr/kg/min, temperature <38ºC and absence of metabolic acidosis. Weaning consisted of a spontaneous breathing trial, which is routinely performed in our unit with a T-tube connected to an oxygen source . The following conditions indicated a successful spontaneous breathing trial: oxygen partial pressure ≥60 mmHg or transcutaneous oxygen saturation>90% with fraction of inspired oxygen <0.5, carbon dioxide partial pressure <50 mmHg (or an increase <8 mmHg), pH >7.32, respiratory rate <35 bpm (or an increase <50%), heart rate <140 bpm (or an increase <20%), systolic blood pressure <180 mmHg, and absence of cardiac arrhythmias after a minimum period of 30-120 min. Once the test was completed, extubation and subsequent placement of a Venturi oxygen mask with 0.3-0.4 fraction of inspired oxygen was performed. The physician in charge was responsible for the process of removal of mechanical ventilation and subsequent extubation. In the case of T-tube test failure, the patient was reconnected to the ventilator. Patient who presented clinical deterioration within 48 hours after extubation (work of breathing, use of accessory muscles, paradoxical breathing) and/or respiratory-gasometric deterioration [respiratory rate >25 bpm or increase of >50% with respect to the baseline respiratory rate, oxygen partial pressure <65 mmHg, carbon dioxide partial pressure >45 mmHg or pH <7.33) [19] and who were candidates for non-invasive ventilation were included in the study. Extubation failure was classified as follows: 1) Acute respiratory failure secondary to airway problems: obstruction of the upper airway and aspiration or excess of secretions; 2) Acute respiratory failure not dependent of the airway: acute pulmonary oedema, congestive heart failure, hypoxemic and/or hypercapnic acute respiratory failure, encephalopathy and others (digestive bleeding, shock, etc.). Patients who required immediate reintubation after extubation failure were not included.

After confirming extubation failure and the possibility of eligibility to participate in the study, the patient was assigned to a group (non-invasive ventilation group or oxygen group) through the opening of a sealed envelope. Previously, a simple randomisation by a computerised system had been performed by a physician not involved in the study.

Non-invasive ventilation. BiPAP Vision and continuous positive airway pressure devices were used. For the BiPAP Vision, oronasal and facial masks and an active humidification system were used. Procedure: Once the patient was informed of the procedure, the type of mask was selected according to the clinical situation and anatomy of the patient, and the harness was placed. Ventilation was initiated with progressive levels of inspiratory positive airway pressure and expiratory positive airway pressure until a minimum inspiratory positive airway pressure of 10-15 cmH2O and an expiratory positive airway pressure of 5-6 cmH2O were achieved in the first hour. The rise time was 0.1-0.2 seconds. Continuous positive airway pressure. A continuous positive airway pressure device was used through the oronasal mask on the patient. The minimum initial positive end-expiratory pressure level was 5 cmH2O, with progressive increases up to 10-15 cmH2O. The objective pressures of both devices were set to reduce dyspnoea and respiratory mechanics, with an respiratory rate between 25 and 28 bpm. The fraction of inspired oxygen was increased in both devices until a transcutaneous oxygen saturation of 94-96% was achieved. Once the patient's cooperation and sufficient adaptability were achieved, the mask was adjusted to the harness with adjustable straps.

Oxygen therapy. The control group received oxygen therapy using a Venturi mask with an fraction of inspired oxygen up to 0.5 or using a reservoir mask connected to a high-flow flowmeter with 30 L/min of O2 (estimated fraction of inspired oxygen of 1.0).