Pain is the 5th vital sign.
The currently accepted pain scale is based on a scoring system of zero to ten.
0/10 equals no pain.
10/10 equals worst ever, unbearable, agonizing distress.
13/10 is not allowed.
Even 10+/10 pain is not allowed.
Folks would never report 0-/10 pain for "less than no pain."
I like to keep things as simple as possible.
Therefore, there is no pain greater than WORST EVER, UNBEARABLE, AGONIZING DISTRESS or 10/10.