Decisions about the initiation, continuation and termination of life-supporting treatments are a permanent challenge in intensive care units (ICUs). Decisions should be based on patient preferences and the medical indication. The medical indication is mainly the result of an assessment of the patient's prognosis and the applicable therapeutic options. Factors influencing the short term prognosis are mostly the severity of the acute leading disease, the number and severity of other organ failures and the response to initial treatment. Long term prognosis is dominated by the severity and number of comorbidities, age and the resulting frailty. Because in many patients all these informations are not available at the time of admission, in these cases a time-limited trial is often justified to gather all this information before a decision is made. These principles of decision making can also applied to situations in which ICU-capacities are limited (e. g. COVID-19 pandemic).