eorge Edwards' 1966 thriller Planet of Blood, a major inspiration for Ridley Scott's original Alien, pits an astronaut crew against an anemic space vixen who, as the men discover one by one, must drink their hemoglobin to survive. In one of the film's genuinely interesting scenes, the crew discovers their sickbay has been raided, and its supply of artificial blood is missing. This is one of the very few instances I can think of where artificial blood has been mentioned in cinema, or really anywhere in science fiction. Which is interesting, because experiments in this area date back at least as far as the early 1600s, when English physicians injected wounded soldiers with the blood of sheep in a vain and horrific attempt to save their lives.
Typically, an adult human body contains about 10 to 12 pints of blood, and can expire from the loss of as little as 25% of it. Fifty percent loss, untreated, is invariably fatal—usually due to lack of circulating pressure rather than lack of oxygen-carrying red cells, which the body usually keeps more of than it actually needs at any given time. Animal-to-human transfusions were quickly banned because of the fatal immune reactions they triggered. Studies in human-to-human transfer continued sporadically, and finally saved a life for the first time in Philadelphia in 1795. Still, the success
record remained spotty, with most recipients dying either of their injuries or from reactions to the foreign blood. Not too surprisingly, the procedure was considered a dangerous last resort until the period between 1900 and 1912, when the discovery and cataloguing of the various blood types made it
possible for the first time to match up donors and recipients safely.
By the late 1990s, industrialized countries were dealing with blood in industrial quantities, pouring tens of thousands of units per day into accident victims, surgery patients and sufferers of assorted injuries and illnesses. Blood banks in the United States were collecting 13 million pints per year, from 8 million individual donors, for the benefit of around 4.5 million patients. Supplies were almost always short; only 3% of Americans ever donated blood, while 95% would use it at some point in their lives. Collection and consumption were locked in a constant race, with supplies usually good for four days or less, and sometimes zero, and sometimes a negative number, which required the cancellation or postponement of vital surgeries.
All this changed in September, when millions of people, horrified at the carnage in New York and anxious to help, rushed out to donate a pint of themselves. It was far more blood than the city actually needed, so the excess was shipped to national distribution centers, and for the first time in decades, the on-hand supply jumped to more than 7 days.
Blood by any other name
Patients are sometimes transfused with "whole blood" straight from the vein, and many people opt, for various reasons, to donate and freeze their own blood for their own later use. More often, though, today's treatments rely on specialized blood products which are separated and refined from the original fluid. Red blood cells are used to treat blood loss and anemia, while plasma (the salty, protein-rich broth) is for burns and traumas, and platelets and clotting factors speed the healing of wounds and ease the side effects of hemophilia and chemotherapy. Other blood products include granulocytes to fight certain infections and cancers, and immune globulins to protect against exposure to viral illnesses such as hepatitis. With the blood divided up this way, every donated pint winds up helping multiple patients.
But it's the red blood cells that are needed most. Supplies fluctuate, and so does demand, but victims of bloody trauma don't have the luxury of postponing their treatment. The blood they need has to be on hand at all times. But what happens if we run out? This question was seriously addressed for the first time in the period leading up to the Gulf War, when military planners feared that U.S. troop casualties could easily use up the available supply. Thankfully, that didn't happen, but the Army's last-ditch answer remains with us: a stockpile of artificial blood.
Actually, this idea isn't new either; physicians in the 1870s experimented with milk as a substitute for dangerous blood transfusions. You have to give them credit for the idea, ignorant as they were of the vagaries of the human immune system. Not surprisingly, this practice also resulted in adverse reactions, sometimes fatal. Still, the field's pioneers soldiered on, and finally hit on saline (salt water) as an acceptable additive in 1884. Saline doesn't carry oxygen—at least not in significant quantity—and has none of the nutritional, clotting or disease-fighting properties of whole blood or even blood plasma. But it does replace lost blood volume and thus maintain pressure, and this turns
out to be sufficient in many cases to save a trauma victim's life.
Hemoglobin is the oxygen-carrying molecule that makes red blood cells red—or blue, when they're carrying CO2 from the tissues back to the lungs—and as early as 1916, researchers were adding hemoglobin to saline as an experimental blood substitute. It was another good idea gone badly wrong—the raw molecule turns out to be both short-lived and toxic in the human body, unless surrounded by the fatty envelope of the red cell. One answer to this is to encapsulate the hemoglobin in artificial fat globules the size of red blood cells—a practice which began in 1957, and continues through today. It even works, kinda sorta, although the mixture's half-life in the body remains short—around 6 hours at best.
Other alternatives, first tried in the '80s and '90s, include engineering friendlier versions of the hemoglobin molecule, chaining multiple hemoglobins together into larger supermolecules, and embedding hemoglobin into the surface of tiny plastic beads. These microspheres are slightly smaller than red cells, but can carry up to 50% more oxygen. Other molecules, such as antioxidants, may be included on the bead's surface as well. Health effects of the beads themselves may require further study, although several supermolecule preparations are already in clinical trials.
Our body's bloody future
Another promising avenue has nothing to do with hemoglobin at all. Oxygen and CO2 can dissolve directly into liquids called perfluorocarbons, which hold and release the two gases about as efficiently as hemoglobin does. When oxygenated, the solution is even breathable by rats, humans and other mammals, as featured in James Cameron's underwater classic, The Abyss. Like oils, perfluorocarbons don't mix well with water, so using them in blood requires breaking them up into microscopic droplets—which can be carried in the plasma in the same way that nutritious oils and fats are.
Under the trade name Fluosol, such preparations have been available for 20 years as a blood additive for use during heart surgery. As a blood substitute they are more controversial; heart patients using the additive suffered an increased likelihood of complications such as stroke. Test animals have survived 100% replacement of their blood with Fluosol, but only while breathing pure oxygen. Unfortunately, building back a natural blood supply can take weeks, and pure oxygen is toxic to the body over such long periods of time. What's more, the half-life of fluorocarbon emulsions in the body is only about 12 hours; it tends to escape into the lungs, where it's exhaled as an ozone-damaging vapor. As if this weren't bad enough, Fluosol has to be stored in a freezer, and warmed to human temperature before use. More recent perfluorocarbon preparations, such as Sanguine Corporation's Pher-O2, are storable at room temperature and have been shown to perform better, but may still face some of the same limitations.
At this point, nobody really knows the effectiveness of these artificial blood products in the treatment of human diseases and traumas, and hopefully we won't find out anytime soon. Not only does North America's blood supply finally exceed minimum safe guidelines, but the Red Cross is working on a
Strategic Blood Reserve where thousands or possibly even millions of units will be stored in deep freeze against any future spikes in demand. If you are eligible to donate, you should do so as often as possible, keeping in mind that the lives you heroically save may well include your own. There really is no substitute for human blood, or even purified red blood cell suspensions.
Still, the future does hold great promise for a variety of blood additives and substitutes, probably including nanoengineered solutions which surpass natural blood's ability to transport oxygen, carbon dioxide, nutrients and biochemical messengers. These could not only serve as treatments for the sick and injured, but also potentially as performance enhancers for healthy individuals such as athletes. Imagine the Olympic committee headaches in a world where sprinting and breath-holding events rely on the respiratory equivalent of a camel's hump! Zyvex Corporation nanoscientist Robert A. Freitas even estimates that a bloodstream supplemented with trillions of tiny pressure tanks—made of diamond and incredibly strong—could keep a patient's brain alive for an hour or more, even in the absence of a measurable heartbeat. It may be possible, in other words, to exercise yourself to death, and still get up to finish the race. Now that's what I call wanting it more.
Wil McCarthy is a rocket guidance engineer, robot designer, science fiction author and occasional aquanaut. He has contributed to three interplanetary spacecraft, five communication and weather satellites, a line of landmine-clearing robots, and some other "really cool stuff" he can't tell us about. His short fiction has graced the pages of Analog, Asimov's, Science Fiction Age and other major publications, and his novel-length works include Aggressor Six, the New York Times notable Bloom, and The Collapsium.
