Lt Col Duncan Phimister ran the hospital between April and July this year, coinciding with the start of Panther's Claw - the pre-election operation to shore up security - and a rise in UK casualty numbers.
Fatalities inevitably change the atmosphere in the camp - the main British base in Afghanistan, he says.
"It does hit home when British soldiers have died. The mood in that hospital this week will have been very sombre.
"I can remember the first fatality after I went out there. It's a really depressing occasion when somebody dies in hospital - it really affects everyone.
"It's amazing how hard these guys will fight to keep people alive... but sometimes you have to recognise you're fighting a losing battle."
However, Col Phimister - who retired on Saturday after 30 years with the Territorial Army - said that is "not at all common".
"If somebody survives as far as the hospital, their ultimate chances of survival are excellent."
This he puts down to factors including the speedy application or tourniquets by comrades, treatment by surgeon-led emergency response teams aboard Chinook helicopter and Camp Bastion's facilities.
Its medics are warned about the numbers and nationalities of the casualties, the nature of their injuries and their expected arrival time. They can call in help from the two "off-shifts" if required.
"By the time the helicopters arrive, everything is set up," says Col Phimister, 62.
"We've got enough staff. We have the blood ready, the pathology lab is on stand-by and the minute they come in the whole system swings into action.
"It's very focused. The adrenaline rushes but it's a really well-oiled machine. I've stood back in amazement at how calm people are when all hell is let loose."
Often, he says, medics must demonstrate this professionalism when faced with horrific wounds.
Lt Col Phimister said he was amazed at how calm his medics remained
"None of them are newly-qualified and experiencing trauma for the first time, but getting five or six guys blown up at the same time and seeing limbs hanging off is certainly not a common occurrence in Britain."
Despite the summer's elevated casualty rate, Col Phimister says such large-scale incidents were not common. However, staff are closely monitored for psychological effects of their work.
Injured personnel are graded according to the severity of their injuries, with up to four of the most serious cases rushed into theatre.
Medics try to treat all patients within the so-called "golden hour period" after injury, to maximise their survival chances.
Aiding that is the "awesome" capability to evacuate some casualties to Birmingham's Selly Oak Hospital - often within 24 hours of injury.
Unlike those shot on Tuesday, most serious casualties are victims of roadside bombs and have often lost a lot of blood.
"We can deal with almost anything but sadly the most common among survivors are blast injuries, a lot which end up in amputation.
"We might have double or triple amputations or a huge loss of blood through abdominal injuries. I can remember people who had massive transfusions - 50 or 60 units - when the normal human body only has 10 or 12."
A rapid infuser, which heats the blood and allows two units to be applied in the first minute of treatment has had a dramatic effect on survival rates, he adds.
In serious cases, surgery can last four hours, meaning theatre teams face 20-hour shifts when major incidents occur.
Consequently, he was always happy to see staff resting whenever they could.
During serious incidents, medical staff can work 20-hour shifts
"If there were guys asleep on trolleys during quiet spells, it wouldn't bother me," he says.
"They're not skiving, they're preserving energy because they don't know when they'll next get their heads down."
Receiving casualties is a daily occurrence at the field hospital. However, not all are severely wounded.
Many cases involve everyday injuries and illness.
Often staff treated Afghan civilians hurt during coalition movements or suicide bombings.
Col Phimister said there was "no question" they would not receive the same treatment as a British soldier.
As required by the Geneva Convention, the staff may also potentially treat injured insurgents, although they would be segregated and heavily guarded.
After a career in the NHS, firstly as a biomedical scientist and latterly as chief executive at the George Elliot Hospital in Nuneaton, West Midlands, Col Phimister says it is difficult to believe Camp Bastion's facilities are in a conflict zone.
The father-of-two said: "If I had a child in the forces in Afghanistan, I'd certainly be reassured."
Those who go back to work in Britain's hospitals take with them a wealth of experience, personal and professional, he adds.
"It will serve them very well back in civilian employment."
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