exclude page from general rewrite rules

Hi

I need to remove a page from the general rewrites rules. My .htaccess is:

<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /portal/
RewriteRule ^index\.php$ – [L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /portal/index.php [L]

RewriteRule mipagina/(.*)/(.*)/?$ index.php?page_id=122&codigo=$1&b=$2 [L]
</IfModule>

but nothing happened . I need because i need this page acept 2 params.

Anyone help plz ?