Hitting one’s parents:
One who hits his father or mother during their lifetime is liable for the death penalty of strangulation. This applies whether to a son or a daughter. However it only applies if blood was drawn through the hit. If however blood was not drawn through the hit, then [one is not liable for death, although] it is included within the negative command against hitting any Jew.
Giving medical treatments to a parent:
A. Removing a splinter from a parent:
It is forbidden to remove a splinter from a father [or mother] due to that one may come to cause him a wound.
B. Amputation and bloodletting:
It is forbidden for a doctor to amputate the limb of one’s father [or mother] or to cut him to perform bloodletting, even though he intends to do so for healing purposes. This however only applies if there is another doctor available to perform the procedure. If however there is no one else available and the parent is in pain [or danger] then he may blood let him and amputate him according to that which the parent allows.
May one scratch his father’s back?
One may only do so if it will not cause bleeding.
 Rama 241/1; Mishneh Sanhedrin 85b
 Rama ibid; Tur 241
 Michaber 241/3; Rambam
 Michaber ibid
 Rama ibid; Rambam Mamarim 5; Ramban
Other opinions: Some Poskim rule it is forbidden to do the above procedures even if no one else is available. [Rif and Rosh; Shulchan Gavoa in accordance to Michaber ibid]