Moist-heat sterilization of blood bags

In their complete configuration, Blood Bags (BBs) are sets of four bags; there are also single, double
and triple sets. The bags are constituted by bonded and plasticized PVC film, heat-sealed along its perimeter. The tubing is made of thicker PVC; the elements for connection, flow control and sampling are made of polypropylene or polycarbonate. The donation needle is made of stainless steel.

Two bags of the same size contain the anticoagulant and the nutrient solutions. The other bags, generally smaller (satellite bags), are initially empty and dry; they are isolated from the main bags by closed break-valves. The amount of air in the bags is left as small as possible. A label is pasted onto each bag and bears manufacturer information. The set of bags is protected by an
outer package (bag or blister).

The complexity of BBs and the critical nature of their use inevitably lead to the choice of moist-heat as sterilization method. Due to a combination of heat- and pressure-related effects, a traditional sterilization process with initial vacuum and pure saturated steam would cause deformation of the
PVC bags and alteration of the solutions contained in them.

The most suitable type of autoclaves for sterilizing blood bag systems are autoclaves in which sterilizing medium is a mixture of steam and air. This method, one of the counterpressure types of sterilization, is also called ‘air-over-steam’. It allows controlling the sterilization pressure independently of the temperature: this independence is impossible with conventional pure-steam autoclaves, as the temperature and pressure of pure saturated steam are linked by a one-to-one relation.