I don't think that there is such a thing as a PDOStatement. PDO is more like data access layer and it stands for PHP Data objects. So you can get a reference to the PDO through the connection:
DB::connection()->getPdo();
or if you want to write a statement you can use:
DB::connection()->statement()
here is the definition of the statement function:
/**
* Execute an SQL statement and return the boolean result.
*
* @param string $query
* @param array $bindings
* @return bool
*/
public function statement($query, $bindings = []);