Dynamic changes in prognosis with elapsed time on ventilators among mechanically ventilated patients

[[abstract]]RATIONALE: Previous outcome studies of mechanical ventilation usually adopted a static time frame to observe the outcome and reported prognosis from the standpoint of the first ventilator day. However, patients and their family may repeatedly inquire about prognosis over time after the initiation of mechanical ventilation. OBJECTIVES: We aimed to describe dynamic changes in prognosis according to the elapsed time on ventilators for mechanically ventilated patients. METHODS: This cohort study used the entire population dataset of Taiwan's National Health Insurance database. We enrolled adults who newly received invasive mechanical ventilation for at least two consecutive days between March 1, 2010 and August 31, 2011. For every single ventilator day after the initiation of mechanical ventilation, we estimated the cumulative probabilities of weaning success and death in the following 90 days. RESULTS: A total of 162,200 episodes of respiratory failure requiring invasive mechanical ventilation were included. The median age was 72 years (IQR, 57-81) and the median follow-up time was 250 days (IQR, 30-463). The probability curve of weaning success against the time on ventilation showed a unidirectionally decreasing trend with a relatively sharp slope in the initial two months. The probabilities of weaning success in 90 days following the second, 7th, 21th and 60th ventilator days were 68.3% (95% CI, 68.1-68.5%), 62.6% (95% CI, 62.2-62.9%), 46.3% (95% CI, 45.8-46.8%) and 21.0% (95% CI, 20.3-21.8%), respectively. In contrast, the death curve has an initial increase and then a decreasing trend after the 19th ventilator day. We also reported tailored prognosis information according to the age, sex and ventilator-day of a mechanically ventilated patient. CONCLUSIONS: This study provides ventilator-day specific prognosis in a large cohort of unselected patients on invasive mechanical ventilation. The probability of weaning success decreases with the elapsed time on mechanical ventilation and the decline is particularly remarkable in the first two months of ventilatory support