P0.1 and Extubation Failure in Critically Ill Patients

Overview

Weaning and extubation are essential steps for the management of critically ill patients when mechanical ventilation (MV) is no longer required. Extubation failure (EF) occurs in approximately 10-30% (1,2) of all patients meeting the readiness criteria and have tolerated a spontaneous breathing trial (SBT). EF is associated with prolonged MV, as well as increased morbidity and mortality (2). Therefore, the early identification of critically ill patients who are likely to experience EF is vital for improved outcomes. EF can result from different factors (respiratory, metabolic, neuromuscular), particularly cardiac factor, and can be caused by the inability of the respiratory muscle pump to tolerate increases in the cardiac and respiratory load (1,3). Respiratory drive represents the intensity of the neural stimulus to breathe. In mechanically ventilated patients, it can be abnormally low (i.e., suppressed or insufficient) or abnormally high (i.e., excessive), and thus result in excessively low or high inspiratory effort, leading to potential injury to the respiratory muscles (i.e., myotrauma) (4,5) or to the lungs. A high incidence of abnormal drive (low or high) may explain the high incidence of diaphragm dysfunction at time of separation from mechanical ventilation (6). Airway occlusion pressure (P0.1) is the drop in airway pressure (Paw) 100 milliseconds after the onset of inspiration during an end-expiratory occlusion of the airway (7). P0.1 measurement is not perceived by the patient and does not influence respiratory pattern. It is, in theory, a reliable measure of respiratory drive because the brevity of the occlusion explains that it is not affected by patient's response to the occlusion and it is independent of respiratory mechanics (8). P0.1 has also been correlated with inspiratory effort (9, 10) and it has been shown that in patients under assisted mechanical ventilation P0.1 might be able to detect potentially excessive inspiratory effort (11). P0.1 is a non-invasive measure and clinically available at bedside since currently nearly all modern ventilators provide a means of measuring it. Originally, a high P0.1 during a spontaneous breathing trial was associated with failure, suggesting that a high respiratory drive could predict weaning failure. However, only a few and old clinical studies investigated the association between P0.1 and extubation failure (EF) and were not conclusive (12,13). We hypothesized that patients with EF would have increased P0.1 values during spontaneous breathing trial (SBT). Therefore, the aims of our study will be to (1) to evaluate the ability of changes in P0.1 (Delta-P0.1) during SBT to predict EF and (2) to assess if Delta-P0.1 is an independent predictor of EF.

Weaning protocol SBTs will be performed in semirecumbent patients on Pressure Support Ventilation (PSV) mode with inspiratory pressure of 5 cmH2O and positive-end-expiratory pressure (PEEP) of 5 cmH2O as per ICU protocol. Inspiratory oxygen fraction (FiO2) will be adjusted for the achievement of an arterial oxygen saturation value \> 90%, as measured by pulse oximetry. The SBT duration will be 30 minutes as per ICU protocol. The criteria that will be used for poor SBT tolerance are: (1) diaphoresis; (2) use of accessory respiratory muscles; (3) RR \> 35/min; (4) oxygen saturation by pulse oximetry \< 90% with FiO2 ≥ 50%; (5) HR \> 140/min or greater than a 20% increase from baseline; (6) Systolic blood pressure \>180 mmHg or \<90 mmHg; (7) development of cardiac arrhythmias; and/or low level of consciousness. The decision to stop SBT will be made by the physicians. Patients who will fail SBT will be shifted to their previous ventilator mode and not be enrolled in the study. Patients who will complete the SBT will be extubated and followed-up for 72 hours. The medical team (physician, nurse, and respiratory therapist) involved in the extubation decision will be blinded to the P0.1 results. EF will be diagnosed if the patient is extubated but required reintubation within the following 72 hours. Criteria for acute respiratory failure after extubation are the development of at least one of the following: (a) respiratory acidosis with pH \< 7.32 and arterial CO2 pressure (PaCO2) \> 45 mmHg; (b) arterial oxygen saturation \< 90% with FiO2 \> 0.5; (c) RR \> 35/min; (d) clinical signs of respiratory fatigue. The management of post-extubation respiratory failure will not be protocolized and will be left to the physician's discretion. Ventilatory, including P0.1 and hemodynamic parameters, including EtCO2 will be recorded as the average of at least three measurements immediately before SBT, during SBT, and at 30 minutes after SBT initiation. Arterial and central venous blood gas (if central line present) will be measured immediately before SBT and at 30 minutes after SBT initiation.