using prefetch_count and ack'ing messages in batches

[loki77]

If I set a consumer up so that it has a prefetch_count of 20, is there a way I can bulk acknowledge getting those 20 messages?  All the examples I've seen with kombu show calling the ack() method on a given message, but if I ack just the last of the first 20 messages I only get one more message and the rest remain un-acked.  Any idea how to make this work?

Thanks!