Prognostication for patients with critical conditions, particularly the aged ones, remained tough. Time-limited trials (TLT) were used to reduce prognostic uncertainty in each individual patient by measuring the treatment’s effect on a defined period of time. However, there was substantial trouble with determining the length of that period. For a study, researchers presented a probabilistic approach for determining a suitable length of stay for a TLT based on uncertainty about critical care and outcome probability profiles. The research consisted of very old patients (age ≥ 80, n=1,209) from the VIP2 research cohort who were admitted to the ICU for between 2 and 14 days, with respiratory or circulatory support from day 1 and with either no drawbacks of life-sustaining treatment or a final call to cancel the treatment, as well as with complete data. The capacity to stimulate multiple level 0f organ support and result stated across time was necessary for the multi-state capability. Shannon’s entropy of probability distributions at discrete points in time was used to measure the amount of uncertainty. Periods of increased prognostic uncertainty of up to 7 days after admission were detected by investigators. The time of the periods depended upon patient behaviors at baseline (frailty, severity of critical illness) and the extent of the help of the organ. Time-dependent signs of uncertainty issuing the outcome to critical care could have informed results about the time period of TLTs, which might have ended up to a week in very aged patients.