Murat Yalcinsoy,1 Cuneyt Salturk,2 Selahattin Oztas,2 Sinem Gungor,2 Ipek Ozmen,2 Feyyaz Kabadayi,2 Aysem Askim Oztim,2 Emine Aksoy,2 Nalan Adıguzel,2 Ozlem Oruc,2 Zuhal Karakurt2 1Department of Pulmonary Medicine, Inonu University Medical Faculty, Turgut Ozal Medical Center, Malatya, 2Department of Pulmonary Medicine, Sureyyapaşa Chest Diseases and Thoracic Surgery Training and Research Hospital, Istanbul, Turkey Purpose: Noninvasive mechanical ventilation (NIMV) usage outside of intensive care unit is not recommended in patients with COPD for severe acute respiratory failure (ARF). We assessed the factors associated with failure of NIMV in patients with ARF and severe acidosis admitted to the emergency department and followed on respiratory ward.Patients and methods: This is a retrospective observational cohort study conducted in a tertiary teaching hospital specialized in chest diseases and thoracic surgery between June 1, 2013 and May 31, 2014. COPD patients who were admitted to our emergency department due to ARF were included. Patients were grouped according to the severity of acidosis into two groups: group 1 (pH=7.20–7.25) and group 2 (pH=7.26–7.30).Results: Group 1 included 59 patients (mean age: 70±10 years, 30.5% female) and group 2 included 171 patients (mean age: 67±11 years, 28.7% female). On multivariable analysis, partial arterial oxygen pressure to the inspired fractionated oxygen (PaO2/FiO2) ratio <200, delta pH value <0.30, and pH value <7.31 on control arterial blood gas after NIMV in the emergency room and peak C-reactive protein were found to be the risk factors for NIMV failure in COPD patients with ARF in the ward.Conclusion: NIMV is effective not only in mild respiratory failure but also with severe forms of COPD patients presenting with severe exacerbation. The determination of the failure criteria of NIMV and the expertise of the team is critical for treatment success. Keywords: noninvasive mechanical ventilation, COPD, acute respiratory failure, exacerbation, mortality