The effects of supraceliac aortic clamping on the anticoagulant effects of heparin

Resuscitation with Hextend decreases endogenous circulating heparin activity and accelerates clot initiation after hemorrhage in the rabbit

Hemorrhagic shock can result in a hypercoagulable state and has been associated with both hemorrhagic and thrombotic complications in the perioperative period. The author hypothesized that hemorrhage and resuscitation could result in a hypercoagulable state via changes in the heparin-antithrombin III anticoagulant mechanism in rabbits. Rabbits sedated with ketamine underwent sham operation (n = 8) or hemorrhage (25 mL/kg blood shed) for 60 min, followed by resuscitation with an equal volume of 5% human albumin (n = 8) or Hextend (n = 8). Coagulation analysis with the Thrombelastograph analyzer and determination of endogenous heparin and antithrombin III activity were performed on arterial blood samples obtained before hemorrhage and 30 min after resuscitation. The reaction time significantly decreased by 34% after hemorrhage and resuscitation with Hextend, whereas no other significant changes in Thrombelastograph variables were noted. Antithrombin III activity was significantly less in the Albumin (83% +/- 8% of control, mean +/- SD) and Hextend (88% +/- 8%) Resuscitated groups compared with the Sham-Operated animals. Of interest, only the Hextend-Resuscitated animals demonstrated a significant decrease in heparin activity (53.4 +/- 13.6 mU/mL before hemorrhage, 42.3 +/- 5.6 mU/mL after resuscitation). A Hextend)-mediated decrease of both heparin and antithrombin III activity may explain the acceleration of clot initiation compared with albumin administration after hemorrhage in the rabbit.

IMPLICATIONS

Hemorrhage may result in a hypercoagulable state after resuscitation. Decreases in both endogenous heparin and antithrombin III activity after hemorrhage and Hextend resuscitation in rabbits resulted in a significantly decreased time to clot coagulation analysis initiation without a significant change in the rate of clot formation or final clot strength.

Endogenous heparin decreases the thrombotic response to hemorrhagic shock in rabbits

PURPOSE

The purpose of this study was to determine if endogenous heparin release would modulate the hemostatic response to hemorrhagic shock in rabbits.

MATERIALS AND METHODS

Anesthetized rabbits (n = 13) underwent hemorrhagic shock (MAP 30-40 mm Hg) for 60 minutes. Blood samples obtained before and 60 minutes after hemorrhagic shock had thrombelasto-graphic variables (R, reaction time [min]; angle, alpha [ degrees ]; and G [dynes/cm(2)]) determined. Hemostatic function was assessed by modified thrombelastography under four conditions: (1) unmodified sample; (2) platelet inhibition with cytochalasin D; (3) heparinase I exposure; and (4) platelet inhibition and heparinase I exposure.

RESULTS

Thrombelastographic variable values in samples without platelet inhibition or heparinase exposure did not significantly change after hemorrhage (before hemorrhage: R = 22.01 +/- 0.7 min, alpha 43.6 +/- 1.3 degrees, G 7,089 +/- 379 dyne/cm(2); after hemorrhage: R 22.1 +/- 2.4, alpha 41.6 +/- 3.9, G = 5,662 +/- 564; mean +/- SEM). However, blood samples exposed to heparinase after hemorrhage demonstrated enhanced hemostatic function with thrombelastographic values (R = 13.4 +/- 1.5, alpha 56.0 +/- 3.4, G = 7012 +/- 565) significantly different (P <.05) from samples not exposed to heparinase. Samples with platelet inhibition demonstrated a similar pattern.

CONCLUSION

Hemorrhagic shock significantly increased circulating endogenous heparin activity, attenuating the thrombotic response to hemorrhage in rabbits. Heparin-mediated regulation of hemostasis may serve as a protective mechanism in shock states.

Pentalyte does not decrease heparinoid release but does decrease circulating thrombotic mediator activity associated with aortic occlusion-reperfusion in rabbits

Hemorrhage and thrombosis are associated with major vascular and trauma surgery. Release of heparinoids and thrombotic mediators may contribute to these complications and have been described in rabbits after aortic occlusion-reperfusion. We hypothesized that the resuscitative fluid used could reduce heparinoid and thrombotic mediator release after aortic occlusion-reperfusion in rabbits as assessed by thromboelastographic variables (R, reaction time; alpha, angle; and G, a measure of clot strength). Anesthetized rabbits were administered lactated Ringer's solution (n = 8) or PentaLyte (n = 8) at reperfusion after 30 min of ischemia. Blood was obtained before ischemia and after 30 min of reperfusion for thromboelastography under four conditions: 1) unmodified sample, 2) platelet inhibition, 3) heparinase, and 4) platelet inhibition and heparinase. During reperfusion, unmodified samples demonstrated a significant increase in R and decrease in alpha and G that was not affected by PentaLyte. In the presence of heparinase, no significant fluid-specific thromboelastographic differences were noted. However, thrombotic mediator release (discerned by a decrease in R and an increase in alpha) during reperfusion in samples with platelet inhibition and heparinase was significantly attenuated by PentaLyte. PentaLyte administration does not decrease heparinoid release but does decrease thrombotic mediator release after aortic occlusion-reperfusion.

Hepatoenteric ischemia-reperfusion increases circulating heparinoid activity in rabbits

PURPOSE

The purpose of this study was to determine if an increase in circulating heparinoid activity contributes to the hemostatic abnormalities associated with hepatoenteric ischemia-reperfusion.

MATERIALS AND METHODS

Anesthetized rabbit (n = 18) underwent thoracic aorta occlusion for 30 minutes with a balloon catheter, followed by 30 minutes of reperfusion. Blood samples were obtained after 30 minutes of equilibration and 30 minutes of reperfusion. Hemostatic function was assessed by changes in the thrombelastographic variables R (reaction time), alpha (a measure of the speed of clot formation), and G (a measure of clot strength). Thrombelastography was performed on blood without platelet inhibition in the presence or absence of heparinase (n = 9 rabbits). Additional samples (n = 9) were exposed to cytochalasin D (platelet inhibitor) with or without heparinase.

RESULTS

Compared with preischemic values, blood samples with intact platelet function obtained during reperfusion demonstrated a decrease in hemostatic function evidenced by a significant (P<.05) increase in R, decrease in alpha, and decrease in G. R, alpha, and G values of samples without platelet inhibition exposed to heparinase did not significantly change after ischemia. Blood samples exposed to cytochalasin D displayed a similar pattern.

CONCLUSION

An increase in circulating heparinoid activity significantly contributes to the hemostatic disorder associated with hepatoenteric ischemia-reperfusion in rabbits.

Thoracic aorta occlusion-reperfusion decreases hemostasis as assessed by thromboelastography in rabbits

Perioperative hemorrhage and thrombosis are serious complications associated with major vascular surgery. We hypothesized that thoracic aortic occlusion-reperfusion in rabbits would adversely affect hemostasis as assessed by thromboelastographic variables (reaction time, alpha angle and G [a measure of clot strength]). Isoflurane-anesthetized rabbits underwent either sham operation (n = 10) or 30 min of aortic occlusion followed by 90 min of reperfusion (n = 10). Blood samples (350 microL) were exposed to 10 microL of either 0.9% NaCl or cytochalasin D (a platelet inhibitor, 10 microM final concentration) and analyzed for 1 h by using thromboelastography after 30 min of postpreparation equilibration and at 30 and 90 min of reperfusion. Aortic occlusion-reperfusion resulted in a significant (P: < 0.05) increase in reaction time, decrease in alpha angle, and decrease in G at 30 and 90 min of reperfusion compared with the sham-operated group. The decrease in hemostatic function after aortic occlusion-reperfusion was observed to the same degree in samples with or without platelet inhibition. There were no significant differences in platelet concentration between the sham-operated and aortic occlusion-reperfusion groups. Aortic occlusion-reperfusion decreased hemostatic function in rabbits primarily by decreasing the coagulation factor-dependent, platelet-independent contribution to clotting.

IMPLICATIONS

Thoracic aortic occlusion-reperfusion decreased hemostatic function in rabbits primarily by decreasing the coagulation factor-dependent, platelet-independent contribution to clotting. This decrease in hemostatic function may contribute to hemorrhagic complications associated with major vascular surgery.