Effect of temperature on thromboelastography and implications for clinical use in newborns undergoing therapeutic hypothermia

Abstract

Background: Encephalopathic neonates undergoing therapeutic hypothermia have increased risk for coagulopathy secondary to perinatal asphyxia and effects of cooling on the coagulation enzyme cascade. Thromboelastography (TEG) allows for a comprehensive assessment of coagulation that can be regulated for temperature. TEG has not been previously evaluated in newborns undergoing hypothermia treatment.

Methods: Encephalopathic neonates treated with systemic hypothermia were enrolled in this prospective observational study. Daily blood specimens were collected for standard coagulation tests and platelet counts during hypothermia and after rewarming. Concurrent TEG assays were performed at 33.5 and 37.0 °C for comparison.

Results: A total of 48 paired TEGs from 24 subjects were performed. Forty percent of the subjects were males, the mean (± SD) birth weight was 3.2 ± 0.7 kg, and the mean gestational age was 38.4 ± 1.4 wk. TEG results differed significantly between assays performed at 37.0 vs. 33.5 °C, indicating more impaired coagulation at 33.5 °C. TEG parameters clot kinetics, angle, maximum amplitude (MA), and coagulation index were significantly associated with clinical bleeding (P < 0.05). These remained significant (except for MA) after controlling for transfusion therapy.

Conclusion: TEG results are affected by temperature, consistent with the known association of hypothermia with coagulopathy. Several TEG parameters are predictive of clinical bleeding in newborns undergoing hypothermia. Selected cutpoints to predict bleeding risk are temperature dependent.

Figures

1

Representative example of thromboelastograph with measured parameters depicted schematically.

2

Effect of temperature on TEG parameters. The gray bars represent 37°C while the white bars represent 33.5°C. All bars represent mean ± 95% confidence interval. Significant differences by paired T-tests are shown with asterisks (*p

3

Receiver operating curves for K, α, MA and CI. The diagonal line represents an Area under the curve (AUC) of 0.5, indicating a non-informative test. Panel A: K performed at 33.5°C. AUC = 0.7377, Cutpoint = 3.4 min, Sensitivity = 62.5% and Specfificity = 90.9%. Panel B: K performed at 37°C. AUC = 0.7876, Cutpoint = 2.6 min, Sensitivity = 76.9%, Specificity = 81.8%. Panel C: α performed at 33.5°C. AUC = 07377, Cutpoint = 52.3 degrees, Sensitivity = 66.7% and Specfificity = 88.4%. Panel D: α performed at 37°C. AUC = 0.7955, Cutpoint = 57.6 degrees, Sensitivity = 76.9%, Specificity = 81.8%. Panel E: MA performed at 33.5°C. AUC = 0.8172, Cutpoint = 56.1 mm, Sensitivity = 70.83% and Specfificity = 81.82. Panel F: MA performed at 37°C. AUC = 0.8217, Cutpoint = 58.1 mm, Sensitivity = 88.46%, Specificity = 61.18%. Panel G: CI performed at 33.5°C. AUC = 0.7173, Cutpoint = −4.6, Sensitivity = 70.83% and Specfificity = 76.19%. Panel H: CI performed at 37°C. AUC = 0.6476, Cutpoint = −3.3, Sensitivity = 68%, Specificity = 66.67%.