Blood Warmer Lab Report

II.BLOOD WARMING TECHNIQUES

The existing blood warmer techniques can be classified as (i) Countercurrent Heat Exchanger, (ii) Dry heater, (iii) Microwave blood warmer, (iv) Blood warmer using peltier, (v) Screw blood warmer (vi) Split blood warmer.

The ideal blood warmer should be able to deliver the blood safely at normothermia at both high and low flow rates. At high flows, the device should be capable to detecting air emboli and automatically shut down the system to prevent infusion of air in the IV tube. The factors affecting normothermia during blood transfusion are likely to be, limited heat-transfer because of materials such as plastic, limited surface area of the heat exchange mechanism, inadequate heat transfer of the exchange mechanism

Due to several layers of thermal resistance intervened between the heating element and the blood to be warmed, the productivity of the system is reduced. If the warming blood is placed in a non-sterile water bath. It is a perfect medium for growing bacteria which can contaminate the whole blood. Apparently, the intravenous tube must be verified prior to the transfusion. If there is a leak with the intravenous tube, it causes mixing of the blood and non-sterile warming fluid in the water bath [12]. The Countercurrent Heat exchanger has various disadvantages including time delay between the control action and response, the outlet temperature of the blood after warming is not monitored, and a large mass of water thermal inertia is needed to minimize the temperature instabilities. The water-bath warmer is not effective at higher flow rates [13]. Hence, the system is unavoidably bulky, heavy and difficult to use. The water bath can spill or overflow and create electrically unsafe conditions

The dry-heat plate warmer is used to increase the heat transfer of the material [13]. Thermostats are used to monitor the temperature of the aluminium plate surface in contact with the intravenous tube containing the blood and turn the heaters on/off accordingly to the pre-set temperature value. The disadvantages includes, flow resistance in dry warmers is typically high and heat transfer to the blood is inefficient. Since plastic is a poor conductor of heat, it leads to a large temperature drop between the aluminium plate surface and the blood in the intravenous tube. The thermal inertia of the heated aluminium plate surface and the intravenous tube creates a time delay which reduces the response time. If the intravenous tube is made of thin plastic (less than 3mm) to improve heat transfer, it very easy to rupture the intravenous tube and spill the blood