Hi Luis,
I believe you are specifically looking for Dead Connection Detection. Please use the link below to understand the same. Go through the configuration example which has been mentioned at the end of the document :
http://www.cisco.com/c/en/us/td/docs/security/asa/asa82/configuration/guide/config/conns_connlimits.html#wp1080752
Rate if it helps!
Regards,
Akshay Rastogi