How to perform purge old or unused objects in Etcd in OCP 3

Issue

Openshift 3.11 cluster with 5 ETCD nodes . The /var/lib/etcd directory on each of them is growing a lot and, interestingly, have different sizes on each one.
The difference in content between these directories makes us suspect that some of the objects stored in each ETCD node are obsolete.
It is needed to purge this obsolete or unused data urgently to control Etcd disk usage.