The effectiveness of non-invasive ventilation (NIV) can result in possible complications that require preventive attention from nursing staff. The aim of this study was to identify complications in critically ill people undergoing NIV therapy and admitted to the emergency department. This is an exploratory-descriptive, observational, quantitative study carried out using two data collection instruments: a questionnaire and an observation grid, on a sample of 35 patients, most of whom were female (57.14%) and aged over 85 (37.14%). The most frequent clinical diagnosis was respiratory failure (45.71%). The most frequent complications were a feeling of claustrophobia, ulceration of the face, pain and accumulation of secretions. The least frequent complications were nasal congestion, conjunctivitis, gastric distension, aerophagia and vomiting.