To determine whether an invasive approach is associated with favourable long-term outcomes among elderly medical patients in the intensive care unit (ICU), compared with a conservative approach.

Nationwide observational study (OCTO-REVERSE study) using data prospectively collected in the National French Healthcare Database (covering 99% of the population, 66 million people).

Comprehensive multicentre study through the linkage of large-scale national registries (including all public or private facilities) from 2013 to 2018 to avoid ambiguities related to the COVID-19 pandemic.

All non-surgical patients aged 80 years or older admitted to an ICU in France during the period (n=107 014 patients at 822 hospitals).

The main outcome was the 1-year survival rate. The association of the two approaches with 1-year survival was estimated using a time-dependent Cox model and a propensity score (PS) adapted to time-to-event analysis, yielding the average treatment effect in the treated and extended weighted Kaplan–Meier curves.

107 014 patients were categorised into two groups based on the type of care received: invasive (n=51 680 (48%) received invasive ventilation and/or vasopressor support) or conservative (n=55 334 (52%) received neither). 1-year survival rate was significantly lower in the invasive group than in the conservative group (27% vs 59% estimated with extended time-dependent Kaplan–Meier method). The risk of death in the invasive group remained significantly higher after time-dependent PS weighting (HR 1.64; 95% CI 1.60 to 1.69; p

Among the whole population of critically ill elderly medical patients in France, the invasive approach was unknowingly associated with end-of-life care in nearly three quarters of cases. Further research is needed to align intensive care with compassionate goals.