// code JS

$(".form-offset").each(function(index, el) {
        var $form = $(this);
        $form.find('select.form-control:visible:first').change(function(){
            $form.submit();
        });
    });


<?php

// le form dans la vu
            print $this->Form->create('Users', array(
                'type'  => 'get',
                'style' => 'padding: 15px;', 'class' => 'pull-left form-offset',
                'url'   => ['controller' => 'patients', 'action' => 'index', $_SERVER['QUERY_STRING']]
            )) .
                $this->Form->input('offset', array(
                    'div'     => false,
                    'label'   => false,
                    'type'    => 'select',
                    'class'   => 'form-control',
                    'default' => 10,
                    'options' => array(1 => 1, 10 => 10, 15 => 15, 20 => 20, 30 => 30)
                )) .
            $this->Form->end() .
            $this->Paginator->numbers(array(
                'tag' => 'li',
                'after' => '</ul>',
                'currentTag' => 'a',
                'separator' => false,
                'currentClass' => 'active',
                'before' => '<ul class="pagination pull-right" style="margin-right: 15px;">'
            )); ?>