A British doctor received instructions through text messages on his mobile phone and went on to perform a life-saving amputation on a boy in D R Congo.
Vascular surgeon David Nott helped the 16-year-old while working 24-hour shifts with medical charity Medecins Sans Frontieres (MSF) in Rutshuru.
The boy's left arm had been ripped off and was badly infected and gangrenous.
Mr Nott, 52, from London, had never performed the operation but followed instructions from a colleague who had.
The surgeon, who is based at Charing Cross Hospital in west London, said: "He was dying. He had about two or three days to live when I saw him."
It is not clear how the boy was injured. It was suggested that he had been bitten by a hippopotamus while fishing, but Mr Nott also heard that he had been caught in crossfire between government and rebel forces.
There were just 6in (15cm) of the boy's arm remaining, much of the surrounding muscle had died and there was little skin to fold over the wound.
Mr Nott knew he needed to perform a forequarter amputation, requiring removal of the collar bone and shoulder blade.
He contacted Professor Meirion Thomas, from London's Royal Marsden Hospital, who had performed the operation before.
"I texted him and he texted back step by step instructions on how to do it," he said.
Even then I had to think long and hard about whether it was right to leave a young boy with only one arm in the middle of this fighting.