• Wolfgang Huber, Claudia Wiedemann, Tobias Lahmer, Joseph Hoellthaler, Henrik Einwächter, Matthias Treiber, Christoph Schlag, Roland Schmid, and Markus Heilmaier.
• Medizinische Klinik und Poliklinik II, Klinikum rechts der Isar der Technischen Universität München, Ismaninger Straße 22, D-81675 München, Germany.
• Math Biosci Eng. 2019 Nov 14; 17 (2): 1132-1146.

AbstractAssessment of peripheral perfusion and comparison of surface and body core temperature (BST; BCT) are diagnostic cornerstones of critical care. Infrared non-contact thermometers facilitate the accurate measurement of BST. Additionally, a corrected measurement of BST on the forehead provides an estimate of BCT (BCT_Forehead). In clinical routine BCT is measured by ear thermometers (BCT_Ear). The PiCCO-device (PiCCO: Pulse contour analysis) provides thermodilution-derived Cardiac Index (CI_TD) using an arterial catheter with a thermistor tip in the distal aorta. Therefore, the PiCCO-catheter might be used for continuous BCT-measurement (BCT_PiCCO) in addition to intermittent CI-measurement. To the best of our knowledge, BCT_PiCCO has not been validated compared to standard techniques of BCT-measurement including measurement of urinary bladder temperature (BCT_Bladder). Therefore, we compared BCT_PiCCO to BCT_Ear and BCT_Bladder in 52 patients equipped with the PiCCO-device (Pulsion; Germany). Furthermore, this setting allowed to compare different BSTs and their differences to BCT with CI_TD. BCT_PiCCO, BCT_Ear (ThermoScan; Braun), BCT_Bladder (UROSID; ASID BONZ), BCT_Forehead and BSTs (Thermofocus; Tecnimed) were measured four times within 24h. BSTs were determined on the great toe, finger pad and forearm. Immediately afterwards TPTD was performed to obtain CI_TD. 32 (62%) male, 20 (38%) female patients; APACHE-II 23.8 ±8.3. Bland-Altman-analysis demonstrated low bias and percentage error (PE) values for the comparisons of BCT_PiCCO vs. BCT_Bladder (bias 0.05 ±0.27° Celsius; PE = 1.4%), BCT_PiCCO vs. BCT_Ear (bias 0.08 ±0.38° Celsius; PE = 2.0%) and BCT_Ear vs. BCT_Bladder (bias 0.04 ±0.42° Celsius; PE = 2.2). While BCT_PiCCO, BCT_Ear and BCT_Bladder can be considered interchangeable, Bland-Altman-analyses of BCT_Forehead vs. BCT_PiCCO (bias =-0.63 ±0.75° Celsius; PE = 3.9%) Celsisus, BCT_Ear (bias = -0.58 ±0.68° Celsius; PE = 3.6%) and BCT_Bladder (bias = -0.55 ±0.74° Celsius; PE = 3.9%) demonstrate a substantial underestimation of BCT by BCT_Forehead. BSTs and differences between BCT and BST (DCST) significantly correlated with CI_TD with r-values between 0.230 and 0.307 and p-values between 0.002 and p < 0.001. The strongest association with CI_TD was found for BST_forearm (r = 0.307; p < 0.001). In a multivariate analysis regarding CI_TD and including biometric data, BSTs and and their differences to core-temperatures (DCST), only higher temperatures on the forearm and the great toe, young age, low height and male gender were independently associated with CI_TD. The estimate of CI based on this model (CI_estimated) correlated with CI_TD (r = 0.594; p < 0.001). CI_estimated provided large ROC-areas under the curve (AUC) regarding the critical thresholds of CI_TD ≤ 2.5 L/min/m2 (AUC = 0.862) and CI_TD ≥ 5.0 L/min/m2 (AUC = 0.782). 1.) BCT_PiCCO, BCT_Ear and BCT_Bladder are interchangeable. 2.) BCT_Forehead significantly underestimates BCT by about 0.5° Celsius. 3.) All measured BSTs and DCSTs were significantly associated with CI_TD. 4.) CI_estimated is promising, in particular for the prediction of critical thresholds of CI.

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