Donor blood, oxytocin, tetanus vaccine, and a number of diagnostic reagents used in maternal/neonatal care all require refrigeration at 2-8°C for optimal efficacy. Donor blood, like food and some other medical products, require refrigeration in order to prevent bacterial growth. Additionally, medicines and vaccines often require refrigeration to prevent the degredation of their chemicals and weakened pathodgens. Too much time at too high a temperature can render these items inoperable.
Mechanism of Action
The cool air in refrigerators slows chemical processes and often greatly slows bacterial reproduction. Most refrigerators cool the air in them by allowing a circulating refrigerant to vaporize (absorbing heat) inside the refrigerator. The refrigerant then is moved outside the refrigerator and condensed, releasing energy to the outside world. Electric (and solar electric) refrigerators typically compress R134a or a similar refrigerant in this process.
Gas and kerosene refrigerators (which can operate in the absence of electricity) circulate ammonia, which vaporizes (absorbing heat) in the presence of hydrogen gas and later condenses (releasing heat) in the presence of water. A gas or kerosene flame then boils the ammonia out of the water to restart the cycle. Ideally, refrigerators are equipped with visual and audible alarms signaling failure as well as temperature indicators which change color if the cold chain has been broken. Ruggedized refrigerators are often built with ice liners which increase the time the refrigerator remains cold without power.
Current Use in High-Resource Settings
Electric, compression refrigerators are both more efficient and less expensive than the gas or kerosene refrigerators, making them the common choice in high-resource settings. Furthermore, these refrigerators can maintain close temperature control and alerts to avoid unexpected warming.
Application in Low-Resource Settings
Where grid electricity is reliable with only short blackouts, electric refrigerators are the norm. Ice-lined electric refrigerators are suitable when power is available for more than 8 hours per day. Where electricity is unavailable, the WHO first recommends propane (LPG) provided that it can be obtained for less $1.50/day of refrigerator run time. Without LPG, the WHO recommends kerosene if available for less than $1.50/day of run time. In general, LPG refrigerators require less maintenance than kerosene and provide a thermostat for temperature control whereas kerosene typically requires adjustment of the wick to control temperature. If all other energy sources are unavailable, the WHO recommends solar as a last resort, primarily because of its relatively high cost and maintenance requirements.