the evaluation of a patient in respiratory failure is a multidisciplinary task.it should be accomplished in a timely manner monitoring the patient sequentially evaluating physical signs and symptoms laboratory data and timing of nonivasive ventilation or mechanical ventilation is instituted care should be taken to evaluate patient comfort synchrony and success of ventilatory support which is a dynamic process demanding frequent reevaluations until the patient is ready to the spontaneous breathing trial (SBT) and to the extubation process