Background <p>Ventilation is a core domain of intensive care, and decisions about its management are frequent, complex, and involve multiple professions. While professional responsibilities in such decisions have been examined, little is known about the contextual factors that shape ventilation-related decision-making and the distribution of responsibilities among professional groups. This study aims to identify and analyse such factors.</p> Methods <p>An ethnography was conducted in two German ICUs between December 2023 and July 2025. Data comprised 97&#xa0;h of observation and 17 episodic interviews with nurses and physicians. Analysis followed the Qualitative Analysis Guide of Leuven (QUAGOL).</p> Results <p>Ventilation-related decision work was shaped by a constellation of interdependent contextual factors. These factors were organised in an analytic heuristic structured by level (system, unit, actor) and dimension (structural, situational). In exploring five factors in greater depth – <i>experience</i>, <i>‘significant others’</i>, <i>rounds</i>, <i>‘bed shortage’</i>, and the <i>pandemic</i> – the analysis illustrates how contextual conditions interact across levels to shape both responsibilities and processes of decision-making in everyday ICU practice.</p> Conclusions <p>Ventilation-related decision work in ICUs is embedded in and shaped by multiple interacting contextual conditions. By providing an analytic heuristic to organise and relate these factors, this study offers a structured perspective for understanding how context shapes ventilation-related decision work in everyday practice and provides a basis for further research, education, and reflective practice.</p> Clinical trial number <p>Not applicable.</p>