Nobody ever said the Light Saber was a practical weapon – it's no match for a good blaster, if you ask me – but it exerts a powerful fascination. Special Operations Command have "completed ongoing testing and field evaluation studies" of the next best thing, according to a Pentagon budget document. It's a Plasma Knife which cuts through flesh with a "blade" of glowing ionized gas. But rather than being a weapon, the Plasma Knife is a surgical instrument that could save lives.

Prompt medical care has proven extremely effective at reducing the mortality rates of combat casualties in Iraq and Afghanistan. A policy of basing medics as far forward as possible and carrying out essential treatment before transfer to a full medical facility has reduced the chances of dying from battlefield injuries from 25% during the Korean war – to just 10% today.

But commandos often find themselves in remote areas without the luxury of medical backup, which is why they require their own emergency medical capability. And that's where the Plasma Knife comes in. If you survive the massive tissue damage caused by a bullet or an improvised bomb, then the biggest immediate risk is bleeding to death. The Plasma Knife is a tool to stop bleeding.

In a sense it goes right back to the old technique of cauterization, where you stop the bleeding by applying red-hot irons. Modern surgeons have electrocautery which uses an electrically-heated wire, for the same purpose. The more advanced version is radiosurgery, which replaces the wire with high-energy radio-frequency radiation which heats tissue directly.

All of these work on the same basic principle of stopping bleeding by creating an impermeable layer of necrotic tissue. Or to put it another way, you melt the flesh the form a bandage. The necrotic – that is, dead – tissue is comprised of two layers, a porous outer layer in which all the moisture has been completely vaporized, and an impervious layer where proteins have been broken down but some water remains. The key thing is not to simply blast the bleeding wound with heat, as that literally burns away the flesh and makes the injury deeper. Energy has to be applied in a controlled fashion.

The Plasma Knife resembles tools used for radiosurgery, but has the advantage that it produces plasma (hot ionised gas– not the liquid sort of plasmafound in blood) which penetrates the outer porous layer of dead tissue without damaging it. In principle this means that more serious blood flow, such as that caused by large blood vessels being severed, can be stemmed without doing major damage.

As the name suggests, the Plasma Knife can also be used as a surgical cutting instrument. As with laser and radiosurgery tools, it can be sterile even in field conditions. And it cauterizes and seals the incision as it goes. A normal medical Plasma Knife relies on mains power, but the commando version is described as being low-power and wearable, suggesting it has a separate power pack. Just don't run the batteries down playing Jedi Knights.

Special Operations Command are also looking at a range of other technologies to improve field medicine, including some which are on the far end of extreme, such as recombinant agents suitable for controlling the bleeding in penetrating brain injuries – “Looks like a bullet in the head – take two aspirin and one of these”.

The Plasma Knife might not impress Luke Skywalker. But it might be a step forward for field medicine.

[Photo: Wikimedia]