Abstract
IntroductionHypothermia has notable effects on platelets, platelet function, fibrinogen, and coagulation factors. Common laboratory techniques cannot identify those effects, because blood samples are usually warmed to 37°C before analysis and do not fully reflect the in vivo situation. Multiple aspects of the pathophysiological changes in humoral and cellular coagulation remain obscure. This in vitro experimental study aimed to compare the measurements of thromboelastometry (TEM), multiple-electrode aggregometry (MEA) and Real Time Live Confocal Imaging for the purpose of identifying and characterizing hypothermia-associated coagulopathy.MethodsBlood samples were drawn from 18 healthy volunteers and incubated for 30 min before being analyzed at the target temperatures (37, 32, 24, 18, and 13.7°C). At each temperature thromboelastometry and multiple-electrode aggregometry were measured. Real Time Live Confocal Imaging was performed at 4, 24, and 37°C. The images obtained by Real Time Live Confocal Imaging were compared with the functional results of thromboelastometry and multiple-electrode aggregometry.ResultsThromboelastometry standard parameters were impaired at temperatures below baseline 37°C (ANOVA overall effect, p < 0.001): clotting time was prolonged by 27% at 13.7°C and by 60% at 18°C (p < 0.044); clot formation time was prolonged by 157% (p < 0.001). A reduction in platelet function with decreasing temperatures was observed (p < 0.001); the area under the curve at 13.7°C was reduced by 96% (ADP test), 92% (ASPI test), and 91% (TRAP test) of the baseline values. Temperature-associated changes in coagulation were visualized with Real Time Live Confocal Imaging. Molecular changes such as the temperature-associated decrease in the fibrin network are paralleled by cellular effects like the lesser activity of the platelets as a result of decreased temperature. The maximum clot firmness (MCF) in TEM only changed slightly within the temperature range tested.ConclusionThe inhibitory effects of temperature on clot formation were visualized with Real Time Live Confocal Microscopy and compared with standard point-of-care testing. Inhibition of clotting factors and impaired platelet function are probably a result of hypothermia-induced impairment of thrombin. Measurement of MCF in TEM does not fully concur with Real Time Live Confocal Microscopy or MEA in hypothermia.
Highlights
Hypothermia has notable effects on platelets, platelet function, fibrinogen, and coagulation factors
Examination of basic coagulation values under regular standard laboratory conditions at a temperature of 37◦C (PT, activated partial thromboplastin time (aPTT), INR, fibrinogen, thrombin time, AT III) and platelet count showed no pathological deviation in any participant
The inhibitory effects of temperature on clot formation were visualized with Real Time Live Confocal Microscopy in this study and compared with standard point-of-care testing
Summary
Hypothermia has notable effects on platelets, platelet function, fibrinogen, and coagulation factors. Multiple aspects of the pathophysiological changes in humoral and cellular coagulation remain obscure This in vitro experimental study aimed to compare the measurements of thromboelastometry (TEM), multipleelectrode aggregometry (MEA) and Real Time Live Confocal Imaging for the purpose of identifying and characterizing hypothermia-associated coagulopathy. Experimental research is focusing on the concept of “Suspended Animation” where profound hypothermia rapidly induced by cardiopulmonary bypass in severe trauma resulting in delayed resuscitation improved survival and preserved neurological function (Moffatt et al, 2018; Mohiyaddin et al, 2018). Trauma-related hypothermia has notable effects on the coagulation system and is an independent risk factor for increased morbidity and mortality in trauma patients (Jurkovich et al, 1987; Wolberg et al, 2004; Gerecht, 2014; Vardon et al, 2016). In mild hypothermia (35– 32◦C), bleeding results primarily from a defect in platelet adhesion, and at
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