The length of time that a patient spends on mechanical ventilation doesn't seem to affect the chances of successfully weaning him or the length of weaning time, according to surprising results of a new study. Researchers had expected to find a correlation between longer periods on a ventilator and weaning difficulty because of the atrophy of respiratory muscles during mechanical ventilation.

Researchers analyzed the length of time 155 patients who were considered weanable spent on prolonged ventilator support and the outcomes of weaning them. Length of time on ventilation didn't significantly differ between patients who were successfully weaned and those who weren't, nor did the length of time affect how long weaning took.

Based on these findings, researchers say that health care providers shouldn't consider the length of time a patient has been on mechanical ventilation when making decisions about weaning. They presented their findings at the annual assembly of the American College of Chest Physicians in Orlando, Fla., last fall.