When Michael Putzker receives a phone call that units of stored blood are needed abroad, he prepares a parcel and brings it to the airport. From there on, it is all alone on its journey, for instance to the blood storage of the German armed forces in Afghanistan. But unlike letter paper, the units of stored blood consist of living cells, and the red blood cells react especially sensitive to the transport conditions. Therefore, major Thomas Klose, Putzkers colleague, looks to improve the conditions on the way to distant countries.
One of the main points to take into account is that blood does not like it too cold or too hot – European guidelines give a limit of two to six degrees in the transport box. Does the temperature go beyond this, the worst case occurs: the blood units are ruined and wasted.
“So far, ice is mostly used for cooling“, says Klose who works together with Putzker at the Central Institute of the Sanitary Service of the German Federal Armed Forces in Koblenz. Its disadvantage is that it is many minus degrees cold which makes a complex calculation necessary. How much ice is needed, how many polystyrenes have to separate the blood units from the ice so that the blood does not freeze? Just as well, the expected outdoor temperature on the way to the destination country and the number of blood units in the transportation box has to be considered. „Quite tricky“ argues Klose.
There are already more modern products than frozen water to buy on the market. Yet the cooling devices do not live up to what the manufacturers promise, explains Klose: „We could hardly ever affirm the producers’ test results.” One booklet, he remembers, said that blood units could be transported over 129 hours with special cooling devices, with 43 degree outdoor temperature. „That is far more than we ever obtained in studies“, clarifies the major.
As he does not want to put patients abroad at risk, Klose has to test the cooling devices in an independent study before the armed forces can use them. Therefore, he and Putzker have tested different insulating boxes and cooling devices in the past years. Again and again, in various combinations, they stuffed the boxes and placed them in a climatic chamber. They stayed there at minus ten or plus 40 degree for two to five days. The best outcomes were achieved when box and cooling devices were pre-cooled at four degree and then a bundle of 40 blood units per box was enclosed by paraffin cooling devices on every side. „The cooling devices form a cube in the end“, Klose describes.
Paraffin that is mainly known as ceraceous part of candles has several states of aggregation. The freezing point is at four degree, here fluid paraffin becomes solid. That is exactly the temperature that blood units ideally keep during their transportation and at which the sensitive cells feel good.
Before packing, the insulating box has to be lined with bubble wrap – to defend from percussions. If, finally, the boxes are transported in the cabin or the cockpit of a plane, and not in the cargo hold, the air pressure is balanced and the cells have a really good chance to arrive alive. Klose observed: at a constant outdoor temperature of 40 degree, following the European guidelines, blood has 36 hours to reach the blood storage with this method. With ice, in contrast, the units would have been too warm already after twelve hours.