There are no official rules for surgery
O Remédio skill is used to handle all medical procedures in the system, but I haven't heard of any books that has expanded the skill to include detailed surgery procedures. If anything, I would say it's a hard test and apply a reduction, depending on your edition, either roll at half the normal chance, or apply -40%.
Runequest, the original system that spawned Roleplaying básico (aka "the Chaosium system") did have rules for Hit Locations, as such, BRP also inherited some of those (optional) rules and the 4th edition expanded those. Major Wounds are caused randomly when the character loses more than half his total hit points in damage. You could use the results of such damage for your purposes.
So, here are a few examples of the consequences of hurt organs as presented by BRP 4e (p. 207):
- 01–10 Severed leg tendons cause limping; fused ankle bones cause
limping; back muscles or spinal nerve damage bend the torso
to the left or right; a shattered knee cannot bend; or make
up a new wound effect. Lose 1D3 DEX. The maximum MOV
is now reduced by the same 1D3 result. Your character is still
able to fight.
- 11–20 Much of the nose has been sliced away; multiple scars deface
both hands; an ear has been cut off; a livid scar lends an evil
cast to your character’s appearance; or make up a new
wound effect. Lose 1D3 APP. The visible and unappealing
deformity cannot be disguised. Your character is still able to
fight.
- 21–30 Wrist or hand damage; a slab of arm or shoulder muscle has
been cut away; a chunk was hewn from thigh or calf muscles;
spinal nerves are damaged; several fingers or toes are
severed; or make up a new wound effect. Lose 1D3 STR; this
loss may change what weapons can be used. Your character
is still able to fight with a weapon, but not a shield.
- 31–40 A punctured lung leads to a weakened respiratory system;
deep stomach wounds become chronically reinfected or belly
wounds weaken digestion and general health; kidneys and
liver are damaged; or make up a new wound effect. Lose 1D3
CON; maximum MOV is now reduced by the same 1D3, and
hit points may be lowered. Your character is still able to
fight.
- 41–50 Concussion damages hearing and limits Listen and Insight to
maximums of 65 percent; injury to the head thereafter
require Luck rolls each time to use any Mental skills; blows or
cuts which affect depth perception leave missile weapon skill
ratings at a maximum of 65%; multiple wounds to the face
and neck limit the skills of any Communication skills to 65%
maximum; or make up a new wound effect. Lose 1D3 INT;
this loss may affect your character’s ability to use any
powers. Your character is still able to fight.
- 51–60 Refer to 01–10 for what happened, which now expands to
the loss of one or both arms or legs. Lose 1D6 DEX and
reduce maximum MOV by that same amount. Your character
is unable to fight.
- 61–70 Refer to 11–20 for what happened, though the major wound
now includes worse mutilations. Lose 1D6 APP; it creates
one or more visible deformities that cannot be disguised.
Your character is still able to fight.
- 71–80 Refer to 21–30 for examples of mutilating cuts and losses.
Lose 1D6 STR; change hit points and damage bonus. Your
character is still able to fight.
81–90 Refer to 31–40 for various wounds to the vitals. Lose 1D6
CON; may affect hit points, damage bonus, and reduces
MOV by that number of units equal to the 1D6 result rolled.
Your character is unable to fight.
- 91–92 Bad facial and vocal-cord injuries. Lose 1D6 APP; lower the
Charisma roll respectively. Your character is still able to fight.
93–94 Broken bones and severed ganglia. Lose 1D6 DEX; from now
on your character can only use one-handed melee weapons.
Your character is still able to fight using his or her remaining
arm.
- 95–96 Nerve damage to left or right arm (roll 1D6; a result of 1–3 is
the left arm, 4–6 is the right arm). Lose 1D6 DEX; hereafter
your character can only wield weapons or equipment in his
or her undamaged arm. Your character is still able to fight
using his or her remaining arm.
- 97–98 Nerve damage to both arms. Lose 1D6 DEX; though the legs
are fine, neither arms nor hands can wield anything. Your
character is unable to fight, unless using his or her legs or
head butts.
- 99 Your character is mutilated with vicious wounds. Lose 1D3
points each from APP, DEX, and CON, and describe the
results. Your character is unable to fight.
- 00 Your character was deliberately mutilated after collapsing.
Remove 1D4 points each from any of four characteristics
(gamemaster’s discretion as to which) and describe the
results. Your character is unable to fight.
Aqueles Major Wounds can either be temporary, being removed after natural rest and the use of the medicine skill, or be permanent if you roll badly on a Luck check. As such, I certainly would use those if you asked me for consequences of a bad Remédio skill check on a character.