It's the cold bit of the night. We've been shuffling up the side of the mountain for the past two hours, a long chain of us with head torch beams climbing upwards, and the cold has had time to sink deep into our multiple layers.
As the doctor, I walk at the back of the group, encouraging stragglers, keeping the pace going and picking up the sick ones. Altitude sickness can hit fast, but from experience, there is some degree of denial of initial symptoms before someone presents as acutely unwell, staggering, vomiting and with a headache.
The dark shape of the trekker in front of me suddenly stops, her head torch beam bends forwards and she vomits. She slumps down, perched on a rock, head in hands.
There is always a psychological dimension as to why people do these things. Ideally as doctor, you don't want to discover this at 2am, -10 degsC and 5,500m up a mountain.
She starts to cry and explains she will feel a failure if she doesn't get to the top, her husband has cancer, her mother died of cancer and she is doing this for them. She doesn't want to let them down.
Not the ideal setting for a counselling session. GP training on consultation models did not include this situation.
Nevertheless, I sit next to her, put my hand on her shoulder and offer her a tissue. I suggest that the biggest failure would be not to descend at all. Not to return alive to the husband who needs her.
I also mutter something about summits being for egos and mountains being for the soul. She nods and agrees to descend.
I first became interested in expedition medicine when, as a medical student, I ascended Kilimanjaro. I was fit and young, and had to be held back from running up there.
Almost predictably, I became very unwell. I was so fatigued at one point that I honestly would have preferred to die on the edge of the path than take another step forward. I had a pounding headache and was vomiting, but I did make the summit.
Stupid. I now know better.
However, I gained an appetite for further adventures and knowledge about altitude, emergency and travel medicine. Medical school had neglected these areas.
After medical school, I worked in a trauma unit in Johannesburg, in South Africa. By complete contrast my next job was in medicine in the UK, in a rather 'elderly and retired' area. I lasted a year there before applying for a job with the British Antarctic Survey.
For more than a year I was the single-handed doctor on the sub-Antarctic island of South Georgia. Behind my medical room was a snowy mountain slope that was great for skiing and penguins wandered between the base buildings, bemused by the down-jacketed humans on planks.
There was no TV, no radio, no internet, no jet contrails across the sky and no shops. Just 13 base staff on a 200km glaciated island.
It wasn't hard. It was all discovery and excitement. The hard bit was coming back. Readjusting to the speed of cities and development. Trying to find a career that would allow me to glimpse some of that world again and to show it to others.
Best of both worlds
I applied to the GP training scheme and became a GP in the south-west of the UK. With my experience, I was offered work as an expedition medic and at times, as a leader on various trips across the globe.
I try to fit in the best of both worlds. I enjoy work as a GP partner. I enjoy teaching students about travel and expedition medicine, but I also enjoy the completely different world of expeditions. I fit in about two trips a year. I've worked on trips to Nepal, China, Vietnam, Cambodia, Morocco and Kenya.
Cycling in Cambodia
I don't think there's any one route into expedition medicine. Experience is key, but you can't get expedition experience without being given work on an expedition. Ability to manage A&E-type problems as well as all of the routine GP problems is important.
Courses such as advanced trauma life support are excellent and a diploma in remote healthcare/wilderness medicine gives a solid background.
The reality is that on an expedition, the medic worries about major trauma and resuscitations, but the most commonly seen problems are the type we see in everyday practice. Diarrhoea and vomiting, sunburn, chest infections, sore throats, forgotten medications, aches and pains, migraines and psychological problems.
I received an email two weeks after the trip up the mountain from the woman who had broken down and felt a failure. She wanted to thank me. She said that she would never forget my words. I wouldn't have remembered what I'd said to her unless she had reminded me - she was one of many ill people that night.
I realised that to me, they are a collective group to keep safe. But to them, I was the individual who was there when they desperately needed help. I was the helping hand that kept them safe as they looked into a different world. This means a lot.
- Dr Corser is a GP in Devon