CANBERRA (Xinhua) — The medical experts behind the rescue of 12 young “Wild Boars” soccer players and their coach from the Tham Luang Cave in Chiang Rai last year said that the evacuees were anesthetized with Ketamine before being swum to safety.

Richard Harris, the South Australian anaesthetist and cave diver who led the medical part of the rescue operation, and his Thai counterparts have provided a new account of the operation in a letter to the New England Journal of Medicine (NEJM).

They wrote that the plan to “urgently extricate” the 12 boys and their coach from the Tham Luang caves was developed amid concerns about approaching monsoon rains and falling oxygen levels.

“The plan involved the use of ketamine-based anesthesia and a positive-pressure full-face mask (supplying 80 percent oxygen); the boys were swum out of the cave wearing poorly fitting wet suits in cold water,” the letter, which was published on Thursday, said.

The 12 members of the team aged between 11 and 16 and their 25-year-old coach were successfully evacuated from the cave, which they became stuck in when partial flooding blocked their exit, on July 10, 2018, 18 days after they first entered.

According to the letter, Harris’s team identified hypothermia as the biggest risk to the 13 evacuees’ health and decided to use Ketamine, an anaesthetic that is also used illegally for recreational purposes, because it impairs shivering.

Harris and Craig Challen, a friend and fellow Australian who is a proficient technical diver, were jointly awarded 2019 Australian of the Year for their involvement in the rescue.