Thermometry of Red Blood Cell Concentrate: Magnetic Resonance Decoding Warm Up Process

Abstract

PurposeTemperature is a key measure in human red blood cell concentrate (RBC) quality control. A precise description of transient temperature distributions in RBC units removed from steady storage exposed to ambient temperature is at present unknown. Magnetic resonance thermometry was employed to visualize and analyse RBC warm up processes, to describe time courses of RBC mean, surface and core temperatures by an analytical model, and to determine and investigate corresponding model parameters.MethodsWarm-up processes of 47 RBC units stored at 1–6°C and exposed to 21.25°C ambient temperature were investigated by proton resonance frequency thermometry. Temperature distributions were visualized and analysed with dedicated software allowing derivation of RBC mean, surface and core temperature-time courses during warm up. Time-dependence of mean temperature was assumed to fulfil a lumped capacitive model of heat transfer. Time courses of relative surface and core temperature changes to ambient temperature were similarly assumed to follow shifted exponential decays characterized by a time constant and a relative time shift, respectively.ResultsThe lumped capacitive model of heat transfer and shifted exponential decays described time-dependence of mean, surface and core temperatures close to perfect (mean R2 were 0.999±0.001, 0.996±0.004 and 0.998±0.002, respectively). Mean time constants were τ mean = 55.3±3.7 min, τ surface = 41.4±2.9 min and τ core = 76.8±7.1 min, mean relative time shifts were Δsurface = 0.07±0.02 and Δcore = 0.04±0.01. None of the constants correlated significantly with temperature differences between ambient and storage temperature.ConclusionLumped capacitive model of heat transfer and shifted exponential decays represent simple analytical formulas to describe transient mean, surface and core temperatures of RBC during warm up, which might be a helpful tool in RBC temperature monitoring and quality control. Independence of constants on differences between ambient and storage temperature suggests validity of models for arbitrary storage and ambient temperatures.

Temperature-Sensitive Indicators for Monitoring RBC Concentrates Out of Controlled Temperature Storage

“…4 However, the 30-minute rule as a time-based surrogate for temperature monitoring of RBC concentrates does not take into account a multitude of parameters besides time that influence individual RBC concentrate warming: volume and width of the RBC concentrate storage bag, thermal isolation (eg, air cushion envelopes), sample handling, and exact storage and ambient temperatures the RBC concentrates are exposed to, including variations in air conditioning and solar radiation. [5][6][7][8] In addition, the dynamics of RBC concentrate warming also depend on the number of units packed together. 9 Thus, time-based rules potentially contribute to unnecessary wastage, since RBC concentrates will be discarded even if core temperature is still within acceptable limits, and may be detrimental for patient safety, since RBC concentrates with elevated core temperatures may remain undetected.…”

“…With regard to the 30-minute rule, core temperature of RBC concentrates removed from refrigerated storage at 6°C will remain below 10°C during a 30-minute exposure only if ambient temperature does not exceed 20°C. 8 Consequently, time-based rules can contribute to unnecessary wastage and are potentially detrimental to patient safety. TIs can address these issues since they monitor temperatures of individual RBC concentrates.…”

“…7 Prediction of RBC concentrate core temperature is also influenced by the gradient of storage to ambient temperature. 8 Since thermal insulation reduces temperature and time drifts between RBC concentrate surface and core temperatures during warming, 7 it can ensure validity of label readings with respect to representing RBC concentrate core temperature. In our study, insulation was achieved through placement of each individual RBC concentrate in an additional plastic tube within the pneumatic tube container.…”

“…This limit can serve as the basis for the recalibration of TIs and, if desired, establishment of a new time limit as second-choice surrogate. The latter could be defined with the help of existing heat transfer models 6,8 and the use of empirical data. There are two major limitations to our study.…”

Logistical and safety implications of temperature‐based acceptance of returned red blood cell units

“…On the contrary, it has also been suggested that time‐based rules can result in reissuing RBC units not maintained within the appropriate temperature range . In addition, time‐based rules do not take into account other parameters affecting RBC warming, including unit volume, bag width, unit handling, fluctuation in ambient temperature during transport, and number of units packed together during transport …”