Quantitative evaluation of hypothermia, hyperthermia, and hemodilution on coagulation.

The purpose of this study was to investigate the effects of temperature change on the coagulation time of blood at two different hematocrit levels by using various coagulation-monitoring devices. The devices used in this study were the Bayer Rapid Point Coag Analyzers, Hemochron Jr. Signature, Hemochron Response, Medtronic ACT II, and Haemoscope Thrombelastograph. One unit of human bank blood was used in this study. The hematocrit level was adjusted to 40% and 20%. A control bath and experimental bath were set up. Control blood was maintained at 37 degrees C and tested every 45 +/- 15 min throughout the experimental period of 6 h to demonstrate the stability of the model. The experimental blood was tested at temperature points of 37, 32, 27, 32, 37, 42, and 37 degrees C. Activated clotting time (ACT) tended to increase when the temperature was initially decreased from 37 to 27 degrees C, which reached a statistically significant level when measured by the Hemochron Response at both the 20% (147 +/- 10.7 to 159.3 +/- 11.0, p < .0332) and 40% hematocrit level (130 +/- 14.9 to 152.1 +/- 19.7, p < .0148). ACT was decreased significantly (p < .05) when the temperature was increased to 42 degrees C as measured by all machines except the Hemochron Jr. Signature at the 20% hematocrit level. ACT was significantly higher (p < .05) at a 20% hematocrit level as compared to that at a 40% hematocrit level on all devices for the majority of temperature points. These data suggested that hypothermia only increased ACT when measured by a macrosample device requiring a milliliter sample (Hemochron Response). However, hemodilution induced anticoagulatory effects and hyperthermia caused an acceleration in coagulation by all devices utilized in this study.

Effects of ultrafiltration on enoxaparin: an in vitro analysis.

The use of low molecular weight heparins (LMWH) as an anticoagulant in the heparin-resistant patient poses challenges during cardiopulmonary bypass (CPB). The ultrafiltrability of LMWH has not been previously examined. The purpose of this study was to determine the effects of continuous ultrafiltration on the concentraton of a LMWH, enoxaparin. An in vitro analysis was performed using fresh whole human blood and an extracorporeal circuit containing four parallel ultrafiltrators and a cardiotomy reservoir with an integrated heat exchanger. Constant conditions included temperature (37 degrees C), flow (0.20 L-min(-1)) transmembrane pressure (200 mmHg), and hematocrit (25 +/- 2%). Samples were collected at the inlet, outlet, and ultrafiltrate line at one and three min for one control trial and again for each of the four hemoconcentrators following the bolus of enoxaparin. Coagulation measurements included a viscoelastic monitor (TEG), activated clotting time (ACT), activated partial thromboplastin time (aPTT), and quantitative analysis utilizing a membrane-based electrode for potentiometric measurement of polyanionic concentrations of enoxaparin. Enoxaparin concentration, from inlet to outlet, increased from 2.95 +/- 0.64 to 5.89 +/- 0.95 (p < .001) at 1 min and 4.24 +/- 0.49 to 7.89 +/- 0.606 (p < .001) at 3 min. Kinetic clot activity, as assessed by the TEG index, decreased from -3.8 +/- 2.5 vs. -10.5 +/- 6.0; (p < .01) pre- to postultrafiltrator samples after 3 min. ACT and aPTT results demonstrated no significant change. In conclusion, this study demonstrates enoxaparin is concentrated with the use of continuous ultrafiltration. Functional coagulation studies also indicate a concentrating effect, primarily via the TEG.

The effect of volume replacement on serum protein concentration during cardiopulmonary bypass.

Although controversy exists concerning the optimal total protein and colloid osmotic pressure that should be maintained during cardiopulmonary bypass (CPB), the primary volume expanders remain albumin and 6% hetastarch. The purpose of this study was to quantify the effect of adding boluses of volume replacement agents under various conditions to total serum protein values during CPB. A standard CPB circuit was utilized in eight 45-kg swine that had a priming volume (physiologic saline solution) of 2309 +/- 245 mL. Volumetric alterations occurred throughout the CPB period by the addition of combinations of physiologic saline solution, 6% hetastarch or 5% swine albumin. Pre- and postadministration samples were assayed for total serum protein, total protein, and albumin throughout the CPB period and at pre- and postvolume administration times. There was a significant decline in total serum protein with the initiation of CPB (6.14 +/- 0.49 g/dL vs. 3.40 +/- 0.43 g/dL, p < .0001). Addition of 12.5 g of swine albumin (N = 5) to two different swine increased total serum protein significantly when compared to adding 500 mL of 6% hetastarch (N = 6) (swine albumin 12.4 +/- 6.3% vs. hetastarch 3.3 +/- 2.1%, p < .005). A reduction in total serum protein occurred after hemodilution with varying amount of physiologic saline solution: 250-450 mL (7.4 +/- 4.5%), 451-650 mL (9.6 +/- 5.6%), and 651-1050 mL (19.4 +/- 4.0%). In summary, knowledge of total serum protein concentration and estimated circulating blood volume can be used to guide albumin and hetastarch administration following hemodilution.