<prompt> In acute exacerbations of COPD, noninvasive positive pressure ventilation NIPPV is initiated whenPaco2 45 mmHgPaO2 80 mmHgFEV1 30FEV1FVC 0.7  <response>: In acute exacerbations of COPD, noninvasive positive pressure ventilation NIPPV is initiated in patients with respiratory failure, which is defined as Paco2 45 mmHg, This results in a significant reduction in moality rate, need for intubation, complications of therapy, and hospital length of stay.Ref: Harrison 19e pg: 1707 