However, all of the preceding data were from small or retrospective studies, assessing the use of HMV after acute hypercapnic respiratory failure in COPD patients.  This Figure shows the results from the RESCUE (Respiratory Support in COPD after acute Exacerbation) trial, the first prospective randomized controlled study assessing nocturnal NIV in COPD patients with prolonged hypercapnia after ventilatory support for acute respiratory failure.^[18]  Patients were included if they suffered from COPD and had acute respiratory failure with the need for mechanical ventilation, and once they had prolonged hypercapnia they were randomized to either receive HMV or standard treatment.