PHP + MySql + Stored Procedures, how do I get access an “out” value?

$mysqli = new mysqli(  "HOST", "USR", "PWD", "DBNAME" );
$ivalue=1;
$res = $mysqli->multi_query( "CALL myproc($ivalue,@x);SELECT @x" );
if( $res ) {
  $results = 0;
  do {
    if ($result = $mysqli->store_result()) {
      printf( "<b>Result #%u</b>:<br/>", ++$results );
      while( $row = $result->fetch_row() ) {
        foreach( $row as $cell ) echo $cell, "&nbsp;";
      }
      $result->close();
      if( $mysqli->more_results() ) echo "<br/>";
    }
  } while( $mysqli->next_result() );
}
$mysqli->close();