The second figure of importance in this era was Ambroise Paré (sometimes spelled "Ambrose"), a French army surgeon from the 1530s until his death in 1590. The practice for cauterizing gunshot wounds on the battlefield had been to use boiling oil; an extremely dangerous and painful procedure. Paré began to employ a less irritating emollient, made of egg yolk, rose oil and turpentine. He also described more efficient techniques for the effective ligation of the blood vessels during an amputation. Modern surgery
The discipline of surgery was put on a sound, scientific footing during the Age of Enlightenment in Europe. An important figure in this regard was the Scottish surgical scientist, John Hunter, generally regarded as the father of modern scientific surgery. He brought an empirical and experimental approach to the science and was renowned around Europe for the quality of his research and his written works. Hunter reconstructed surgical knowledge from scratch; refusing to rely on the testimonies of others, he conducted his own surgical experiments to determine the truth of the matter. To aid comparative analysis, he built up a collection of over 13,000 specimens of separate organ systems, from the simplest plants and animals to humans. He greatly advanced knowledge of venereal disease and introduced many new techniques of surgery, including new methods for repairing damage to the Achilles tendon and a more effective method for applying ligature of the arteries in case of an aneurysm.
For hospital stays in 2012 in the United States, private insurance had the highest percentage of surgical expenditure. in 2012, mean hospital costs in the United States were highest for surgical stays. Special populations
Elderly people
Older adults have widely varying physical health. Frail elderly people are at significant risk of post-surgical complications and the need for extended care. Assessment of older people before elective surgery can accurately predict the persons recovery trajectories. One frailty scale uses five items:  unintentional weight loss, muscle weakness, exhaustion, low physical activity, and slowed walking speed. A healthy person scores 0; a very frail person scores 5. Compared to non-frail elderly people, people with intermediate frailty scores (2 or 3) are twice as likely to have post-surgical complications, spend 50% more time in the hospital, and are three times as likely to be discharged to a skilled nursing facility instead of to their own homes. People who are frail and elderly (score of 4 or 5) have even worse outcomes, with the risk of being discharged to a nursing home rising to twenty times the rate for non-frail elderly people. Children
Surgery on children requires considerations that are not common in adult surgery. Children and adolescents are still developing physically and mentally making it difficult for them to make informed decisions and give consent for surgical treatments. Bariatric surgery in youth is among the controversial topics related to surgery in children. Vulnerable populations
Doctors perform surgery with the consent of the person undergoing surgery.