Learn as we explore common misconceptions about IR thermometers and surface temperature vs. core temperature
The following PathLabTalk post describes something we encounter repeatedly in blood banks – and illustrates several problematic misconceptions about determining blood product temperature on return to the blood bank. At the same time, this post demonstrates a reliable, good practice!
“Our transfusion service is looking for an infrared thermometer that we can use to determine the internal temperature of our donor units. We issue products in validated coolers to surgery, ED, and other locations and sometimes we receive the products back that have not been used. Currently, we attach a temperature indicator to the unit, but want something more accurate that is not difficult to operate, calibrate, etc….”1
First, we congratulate this PathLabTalk poster for reaching out to the blood bank community for ideas and support. She/he has realistic, everyday needs that many may identify with. In this VUEPOINT, we present some problems and misconceptions, along with this blood banker’s good practices, that are communicated in the post.
Infrared Thermometers (a.k.a. infrared “guns”) do not measure “internal temperature”
Infrared thermometers are used to measure surface temperature without contacting the product being measured. Most specifications for these devices state “non-contact surface temperature measurement.” They do not measure “core temperature” of any product, including blood. Infrared thermometers are used in many different applications ranging from food service, to residential heating/cooling, to industrial. Typically they are used for “hard to reach” areas where contact temperature measurement is difficult/impossible.
A one-time temperature reading of a returned blood product provides little assurance that the blood was kept at the correct storage or transport temperature over the entire time period that it was out of blood bank control.
No matter how well everyone is trained and how conscientious they are, we all know that once the blood product leaves the blood bank, anything can happen. For example, in the OR or ED there are many critical functions being performed at once, and often over long periods of time. Blood can be taken from the cooler and left on a table for hours – and then returned to the blood bank, having had time to “cool” to what may appear to be an acceptable temperature.
The precariousness of this situation is compounded when an IR thermometer is used to check SURFACE temperature when the product is returned.
• Perhaps the blood bag was placed on an OR table for 6 hours during a long procedure, but was placed back in the cooler just long enough for the SURFACE to cool to a seemingly “acceptable” temperature…?
• Is it safe to assume that the blood temperature never reached unsafe temperatures?
Accuracy of IR thermometers is affected by how they are used – due to “distance to target” a.k.a. FOV (Field of View) or D/S Ratio (Distance to Spot)
Accuracy specifications for most IR thermometers range from +/- 1.0oC to +/- 2oC. Looking at a few models from major manufacturers, their D/S specifications are documented as: 1 meter, 1.5 meters and 2 meters – which might surprise blood bankers using IR thermometers. The distance between the device and the target (blood product) affects the reading accuracy – and also means that the dependability and repeatability of temperature readings is “user dependent” in how they use the IR thermometer from variable distances (you’ll read about this problem in the PathLabTalk post responses). If you’d like to learn more about this particular characteristic, Grainger (industrial and facilities maintenance equipment resource) has an excellent “Quick Tip” on IR thermometers.
Temperature indicators provide irreversible visual evidence if the blood product exceeds its specified temperature, even if the product is “re-cooled” prior to return to the blood bank.
Attaching an irreversible temperature indicator to the blood product, as done by the PathLabTalk poster, IS one way to know if the blood was maintained at correct storage/transport temperatures. When the blood product reaches the indication temperature (typically 6oC or 10oC), the indicator provides “irreversible” visual evidence of the temperature excursion – even if the blood product is “re-cooled” after being out of blood bank control.
This elicits a similar question that we raised regarding IR thermometers – do temperature indicators that adhere to the surface of the blood product provide indication of the surface temperature or core temperature?
Safe-T-Vue indicators (Temptime Corporation) are chemical indicators, and the algorithms that are used to formulate them are based on thousands of laboratory tests that incorporate the CORE blood product temperature. While the indicator may be applied to the surface, its color response is correlated to core temperature.
Why this all matters
Bacteria are very rarely transmitted during blood component transfusion, but if they are, they usually cause severe, life-threatening adverse reactions, with the mortality rate of 20-30%.2
Periodically, there are reports of incidents likely to have caused serious injury or death, that have been linked to bacterial sepsis from blood products that were dispensed for extremely long surgeries, and returned to the blood bank unused.3 Those very products could be returned to inventory after checking the temperature with an IR thermometer, and reissued to another patient. Unbeknownst to the blood bank, the blood products may have reached temperatures that allowed for contaminants to thrive. When that unit is then reissued and transfused to the next patient, the results can be catastrophic.
Kudos to the PathLabTalk poster for good practice
In summary, we understand that it’s unrealistic to assume that blood products will be handled outside of the blood bank with the same watchful eye and expertise that trained, focused blood bankers have. And there is little certainty of blood product maintenance at appropriate storage/transport temperatures, even when using a temperature sensing device to check the product on return to the blood bank.
The most sure way to know that the blood did not reach non-compliant temperatures – that could result in bacterial sepsis – is to use an irreversible temperature indicator that stays with the blood product during its entire time out of the blood bank – as the PathLabTalk post noted.