Dr. Gao, who had been busy all day conducting physicals on other volunteers, called Mr. Castle’s phone twice, but got no answer, so she telephoned the roommate and asked him to have Mr. Castle call her. He never did, and she did not follow up.

At 8 a.m. the following day, Jan. 28, Mr. Castle’s roommate, increasingly worried, called Dr. Gao and put Mr. Castle on the phone. A case summary notes that Dr. Gao thought he sounded “mildly distressed,” and that she went to see him at 9:30 a.m. “His lips appeared dry, and he looked fatigued,” the summary said. Dr. Gao made a diagnosis of acute gastroenteritis and prescribed Cipro, along with an anti-nausea drug.

Image Carrie Hessler-Radelet, the Peace Corps director, said the agency was examining all aspects of its operations, including health care. Credit... Angel Valentin for The New York Times

But she did not recommend that he be sent to the hospital, a decision that would later draw a rebuke, although a mild one, from the outside expert the Peace Corps consulted. Dr. Gao resumed her duties and did not return to Mr. Castle’s room until she was summoned there later that day, about 2 p.m., after a hotel maid discovered Mr. Castle lying in bed in sheets soaked with vomit. The scene in the hotel room quickly became chaotic.

Dr. Gao could not read Mr. Castle’s blood pressure and thought her battery-operated blood pressure cuff was not working. She called for another doctor to bring a manual cuff, which at 2:45 p.m. recorded Mr. Castle’s blood pressure at 80 over 40 — abnormally low. His hands were cold.

“We realized this is a critical situation,” Dr. Gao wrote in her notes.

She called for a physician assistant and told the medical office to send a nurse with intravenous fluids and to arrange for a Peace Corps driver to take Mr. Castle to a hospital. But the Peace Corps vehicle was in use by the agency’s country director, an internal inquiry later found, and none of the medical staff members “felt empowered enough” to ask her to give it up “even during an emergency.”

The physician assistant, an American named Kandice Christian, showed up at 3:15 p.m. She found Mr. Castle to be “lucid,” but with no detectable blood pressure, and the team called for an ambulance. Moments later, as they tried to clear Mr. Castle’s mouth of vomit, he sat up, gasped for breath and collapsed. The ambulance, in the meantime, was lost in Chengdu’s streets and did not arrive until 3:45 p.m. By then, the nurse had come with the fluids, but after a debate between the ambulance doctor and the Peace Corps medical staff, they postponed giving them to Mr. Castle in favor of getting him into the ambulance. Since the ambulance stretcher would not fit in the elevator, he had to be carried down three flights of stairs.