Catechism of the Catholic Church 1503 Christ's compassion toward the sick and his many healings of every kind of infirmity are a resplendent sign that "God has visited his people" and that the Kingdom of God is close at hand. Jesus has the power not only to heal, but also to forgive sins; he has come to heal the whole man, soul and body; he is the physician the sick have need of. His compassion toward all who suffer goes so far that he identifies himself with them: "I was sick and you visited me." His preferential love for the sick has not ceased through the centuries to draw the very special attention of Christians toward all those who suffer in body and soul. It is the source of tireless efforts to comfort them.
1504 Often Jesus asks the sick to believe. He makes use of signs to heal: spittle and the laying on of hands, mud and washing. The sick try to touch him, "for power came forth from him and healed them all." and so in the sacraments Christ continues to "touch" us in order to heal us.
1509 "Heal the sick!" The Church has received this charge from the Lord and strives to carry it out by taking care of the sick as well as by accompanying them with her prayer of intercession. She believes in the life-giving presence of Christ, the physician of souls and bodies. This presence is particularly active through the sacraments, and in an altogether special way through the Eucharist, the bread that gives eternal life and that St. Paul suggests is connected with bodily health.
1510 However, the apostolic Church has its own rite for the sick, attested to by St. James: "Is any among you sick? Let him call for the elders [presbyters] of the Church and let them pray over him, anointing him with oil in the name of the Lord; and the prayer of faith will save the sick man, and the Lord will raise him up; and if he has committed sins, he will be forgiven." Tradition has recognized in this rite one of the seven sacraments.
WHO CAN RECIEVE THE SACRAMENT?
Canon 1004 §1. The anointing of the sick can be administered to a member of the faithful who, having reached the use of reason, begins to be in danger due to sickness or old age. §2. This sacrament can be repeated if the sick person, having recovered, again becomes gravely ill or if the condition becomes more grave during the same illness.
The sickness or injury has to be directly affecting a person that their life reasonably comes into question, such as cancer. Not all surgeries meet the requirements for this sacrament, nor does going under anesthesia constitute a right to this sacrament. It is similar to a soldier going into war. Just because the soldier could be injured or die by a bullet or other ordinance, does not mean we anoint that soldier. The danger of death is extrinsic to the soldier not intrinsic. If an extrinsic threat exists one should request the sacrament of Reconciliation.