But with the immigration of these Jewish men to the United States the opportunity became available to them. Forty, fifty, sixty, seventy year old Jewish men, maybe even eighty year olds were then being brought to the operating rooms at Cedars to have circumcisions. Why the operating room? Circumcision in adults is more involved than it is in newborns only eight days old. Adults have adult diseases—coronary artery disease, diabetes, arthritis, COPD, and others, and in adults the surgery of a circumcision is more complex and the risk of surgery and anesthesia is greater.
The procedure was safer to do in the operating room because of all the monitoring equipment used by the anesthesiologist. It could be done under local anesthesia, but usually it was done under a general anesthetic.
The circumcision was performed by a Jewish urologist and there was a mohel in the operating room to make sure everything was done correctly halachically by the surgeon. And of course, there were an anesthesiologist and nurses in the room. Why was there an anesthesiologist? Because of the pain involved. When Abraham performed a circumcision on the other men and himself four thousand years ago at ninety-nine years of age, there were no anesthetics. Neither were there any drugs for postoperative pain control. Having that procedure then was an extreme personal sacrifice because of the pain involved. In addition to post operative pain, there were other hurdles in the healing process and complications of the surgery itself.
These included excessive bleeding, infections, scarring, increase in erectile dysfunction and decreased sensitivity. And what about Abraham performing all of these circumcisions (including the one on himself}, never having done one before!!!! I’m sure all of those men were quaking in their sandals!!!
So how does Abraham’s circumcision at the end of Lech Lecha have any relevance to Vayera? Remember that in the beginning verse of Vayera Abraham is sitting at the entrance of his tent and the day was growing hot.
What was he doing just sitting there (probably moaning oyyy,oyyy)? He was probably dealing with the severe pain of the third day after his circumcision . (In modern times it can take a man thirty days to heal adequately after a circumcision). 
What was about to happen was a double Mitzvah. God and his two angels were perhaps paying a visit to the ailing Abraham(visiting the sick). Abraham, on the other end, would quickly be warmly extending hospitality to these strangers. The visit to the sick has been suggested in several Torah commentaries as the primary reason for the visit. In the Talmud visiting the sick is said to provide 1/60 of the healing necessary for the patient (Berachot 57b). Maybe in the case of a visit from God and two angels there would have been a larger fraction (60/60 ?) !!! Probably God telling Abraham and Sarah that at the ages of one hundred years and ninety years old they would have a son in a year also made Abraham (and Sarah) feel better !!
 R. Hama, the son of Hanina said: it was the third day after his circumcision and the Holy One, blessed be He, came and inquired after the state of his health). Chumash with Rashi’s Commentary, by Rabbi A.M. Silbermann, 1934, Feldheim Publishers Ltd, Jerusalem Israel.