Why does NBOCA report 90-day mortality rather than 30-day mortality?

From a patient’s perspective the risk of post-operative death at 3 months is just as significant an outcome as death within 1 month of surgery. Post-operative death at 3 months captures those deaths that occur after prolonged critical care support which is now a much more common feature of colorectal cancer resection and adds significantly to the procedure-associated death rate.