working with result of wp_dropdown_pages()

Not sure what your trying to do with the custom field but you can create your own drop down select using the get_pages() function which returns an array of pages similar to the get_posts() function.

$pages = get_pages();
    foreach( $pages as $page ) {
        echo get_post_meta( $page->ID, 'your_meta_key', true );
    }