detecting if content was sent prior to a line in a php file in codeigniter

[eluser]Unknown[/eluser]
m trying to change the way the error files from system/application/errors work by logging the errors and showing a 500 page instead. However, sometimes the error occurs in the middle of a page and i need to display only the error page.

I've tried to check if the headers are sent and cleaning the output buffer but it didn't work. Any sugestions?