Predictors of Weaning Outcomes for Brain Injured Patients: a Prospective, Observational Cohort Study

In general intensive care unit (ICU), about 20% patients are ventilated because of neurological illness. This proportion might be much higher in brain injured patients. As with general intensive care patients, brain injured patients are predisposed to a number of complications associated with mechanical ventilation. Both unnecessarily delaying and premature attempts of withdrawal of mechanical ventilation will increase the rate of complications, prolonged mechanical ventilation, the length of stay, motility, and the cost.

Numerous studies had examined factors that predict combined liberation/extubation outcomes, including vital capacity (VC), minute ventilation(VE), and maximum inspiratory pressure (MIP), airway pressure developed 100 ms after the beginning of inspiration against an occluded airway (P0.1), breathing pattern variability (BPV), and the "rapid shallow breathing index" (RSBI, Breathing frequency-tidal volume ratio, f/Vt). The introduction of Neurally Adjusted Ventilatory Assist (NAVA) has made available a standardized and validated method to monitor and measure diaphragm electrical activity (EAdi) both during conventional modes of ventilation and spontaneous breathing trail (SBT). Neuroventilatory efficiency index (NVE, Tidal volume - EAdi ratio, Vt/EAdi) and neuromechanical efficiency index (NME, tidal volume - EAdi ratio, Paw/EAdi) had also been proposed and showed a promising prospect.

However, all those physiological and mechanical parameters are either have limitations on using in brain injured patients, or have not yet been proved to be validity or even had a poor predictive ability. In part this is because respiratory failure of brain injured patient results from two principle etiologic entities: primary pulmonary dysfunction and neurogenic pulmonary dysfunction. The latter brings us quite different characters of brain injury patients, which required specially consideration. Another reason is that, patients with brain injured but no other indication for mechanical ventilation constitute a group in whom the needs for ventilatory support and for an artificial airway might be separate. Previous study that, in neurosurgical patients passed SBT, a median of 2 days elapsed before the attempted extubation, and 45% patients suffered reintubation or tracheostomies. Nonetheless, in most studies, disconnection of ventilatory support and extubation are often lumped together. Although some studies investigated the factors that are predictive of successful extubation, few study considered about the solely liberation of mechanical ventilation.

Therefore, in present study, the investigators separate the liberation of ventilatory support as a standalone part from the traditional weaning/extubation process. Patients are divided into two groups: weaning success and weaning failure, without consideration of the artificial airway status. The primary aims of the study are: a) validate the EAdi derived values, and b) evaluate the traditional predictive parameters in weaning prediction in brain injured patients.