The world’s wealthiest two billion people get 75 percent of all the surgery done each year, while the poorest two billion get only 4 percent and often die or live in misery as a result, according to a new study published in the medical journal Lancet.

Many countries lack enough surgeons to handle difficult childbirths, tumors, car accidents and other common causes of death, the study found. They often cannot remove cataracts, fix birth defects and skeletal problems or do other operations that improve lives.

Even where surgeons were available, usable operating rooms often were not.

The study asked 769 hospitals in 92 countries how many operating rooms each had and how many were equipped with pulse oximeters — the finger clips that measure how much oxygen is in a patient’s blood. The study assumed that operating theaters without that could also lack other essentials like suction pumps, instrument sterilizers, gloves, oxygen and blood banks.

In most of Africa, there was only 1 operating room per 100,000 people. In the poorer parts of Asia and Latin America, there were 4 to 10 per 100,000. In Western Europe, North America, Australia and New Zealand, there were about 15. In Eastern Europe and the wealthiest Asian countries, there were about 25.

In South Asia and most of Africa, half or more of all operating rooms lacked pulse oximetry.

The study was done by a team from the Harvard School of Public Health along with researchers from New Zealand, Canada and the World Health Organization.