By the time dawn broke over Annapurna I (8,091m), Dawa Nurbu Sherpa had been standing inside a crevasse for nearly twelve hours.

At 7,500 metres, where the air contains barely a third of the oxygen available at sea level, sitting down risked freezing to death and moving risked falling into darkness. So he remained upright, his crampons driven into the ice to stop himself sliding deeper into the chasm. Snow had blown into his gloves and frozen around his hands. His radio battery had died. The rescue helicopter promised from base camp could not reach him.

It was April, but on one of the world's deadliest mountains the season offered little comfort.

Three weeks later, surgeons in Kathmandu amputated seven of his fingers.

Sherpa, 26, had done what Sherpas have done for generations in the Himalayas: put the client first. Near Annapurna's summit, after the Swiss climber he was guiding ran out of bottled oxygen, Sherpa handed over his own supply and continued climbing without it. The client reached the summit. So did Sherpa. It was the descent that changed his life.

His story has become an uncomfortable illustration of the unequal compact that sustains Nepal's booming mountaineering industry. Every spring, wealthy climbers arrive to pursue a lifetime ambition. Behind every successful ascent stands an army of Sherpa guides carrying equipment, fixing ropes, making decisions and, increasingly, assuming the risks that others pay to avoid.

Sherpa grew up in Bungim, a remote village beneath Makalu in Sankhuwasabha district, where farming offered little prospect beyond survival. He left school before completing fifth grade and moved to Kathmandu as a teenager, first working in expedition kitchens before learning the trade that promised something more: high-altitude guiding.

The work is among the best-paid available to young men from Nepal's mountain districts, but also among the most hazardous. Success depends not only on strength and judgement but on weather, luck and clients willing to listen.

This spring, that last ingredient was missing.

Sherpa says he advised his client to climb with the other expeditions scheduled to leave on April 18. The mountain would be safer with other teams nearby. His client preferred solitude. They departed the following day.

Near the summit, Bolt exhausted his oxygen supply. Sherpa surrendered his own cylinder without hesitation. They stood on Annapurna's summit shortly after seven in the morning, took photographs and began descending separately. Sherpa, exhausted after a 16-hour summit push without oxygen, soon fell behind.

Then the weather closed in. Visibility deteriorated. Searching for the descent route, Sherpa spotted what he believed was a fixed rope leading down the couloir. It was not. The rope had been abandoned by an earlier fixing team and ended abruptly. By the time he realised his mistake, darkness had fallen and snow was sweeping across the mountain.

He found shelter only by chance. The crevasse was deep enough to shield him from the worst of the wind but too dangerous to sleep inside. He wedged his crampons into the ice and remained standing throughout the night. Snow collected inside his gloves, freezing against his skin. His fading radio carried one final reassurance from base camp: hold on until morning and a helicopter would come.

"That hope kept me alive," he told Everest Chronicle.

Morning did arrive. The helicopter did not.

Strong winds prevented it from climbing above Camp III. Instead, another IFMGA-certified mountain guide, Ashok Lama, was flown as high as conditions allowed while Sherpa searched for the correct route under his own strength. Eventually he found the fixed line and descended until the two men met.

"I nearly turned back — then I saw him," Ashok recalled of the rescue.

Oxygen, food and water restored enough strength to continue. By Camp III, however, another injury had emerged: severe snow blindness left him unable to open his eyes.

Insurance covered his medical treatment. It could not compensate for what came next.

Doctors amputated seven fingers to prevent infection. His employer has promised work suited to his disability, but the profession for which he had trained since adolescence has effectively ended. Married with two young children, Sherpa now worries less about mountains than school fees.

Guides in his position, he says, have no financial safety net beyond whatever an individual company chooses to offer. "People like us, who lost limbs and parts working in high altitude, do not have any safety net, not from the government nor from the private sector," he says. "Our work ensures climbers visit Nepal to fulfil their lifetime dream."

Nearly three months after returning from Annapurna, he still has not gone home.

His daughter is five. His son is two and a half. They know he lost his fingers. He has not yet found the courage to show them.

"I keep telling them," he said. "I'll show you later."

Nepal's mountaineering industry has become a finely tuned business, generating millions of pounds each climbing season and selling access to the world's highest summits with remarkable efficiency. Yet beneath the polished logistics remains an old truth: mountains do not distinguish between client and guide.

The difference is that one usually returns with a summit photograph.

The other sometimes returns without seven fingers.