Effects of increasing doses of activated recombinant factor VII on haemostatic parameters in swine

The Utility of Thromboelastography to Guide Blood Product Transfusion

OBJECTIVES

To provide an overview of the clot viscoelastic testing technology and to describe its utility in guiding blood product transfusions.

METHODS

A case scenario will be discussed as well as interpretation of thromboelastography (TEG) tracings. In addition, literature examining the utility of viscoelastic testing in guiding patient management and blood product transfusions will be reviewed.

RESULTS

TEG/rotational thromboelastometry (ROTEM) is useful in evaluating clot kinetics in trauma and acutely bleeding patients. TEG/ROTEM parameters are reflective of values measured using standard coagulation assays; however, TEG/ROTEM parameters are more rapidly available and more costly. TEG and ROTEM are used in three main settings: cardiac surgery, liver transplantation, and trauma to assess global hemostasis and administration of blood products.

CONCLUSIONS

TEG/ROTEM can be helpful in guiding resuscitation and blood product transfusion. Several studies have demonstrated a reduction in transfusion of blood components with TEG/ROTEM; however, other studies have suggested that TEG/ROTEM is not clinically effective in guiding transfusion.

Prothrombin complex concentrate and recombinant prothrombin alone or in combination with recombinant factor X and FVIIa in dilutional coagulopathy: a porcine model

BACKGROUND

This study was conducted to assess whether newly developed recombinant clotting factor concentrates enable the reversal of dilutional coagulopathy.

METHODS

In 50 anesthetized pigs, ~60% of the blood volume was withdrawn and replaced with hydroxyethyl starch. Pigs were randomized to receive either 200 mg kg(-1) fibrinogen (n = 10), fibrinogen and 35 IU kg(-1) prothrombin complex concentrate (PCC) (n = 10), fibrinogen and 4 mg kg(-1) recombinant human factor II (rhFII) concentrate (n = 10), fibrinogen and a three-factor combination (3F) of 4 mg kg(-1) rhFII, 0.006 mg kg(-1) recombinant human FVIIa and 0.32 mg kg(-1) recombinant human FX (n = 10), or saline (n = 10). Thereafter, a standardized liver laceration was performed to induce uncontrolled hemorrhage. Survival time and blood loss were determined, and standard coagulation tests and thrombelastometry were performed.

RESULTS

Fibrinogen combined with rhFII or PCC improved survival. Blood loss was significantly decreased in all groups as compared with the animals receiving saline. Clotting time was significantly shortened in the animals treated with fibrinogen and PCC, as well as in those treated with fibrinogen and 3F. One animal died after administration of fibrinogen and PCC.

CONCLUSION

Following hemodilution, a combination of fibrinogen and PCC, rhFII or 3F enhances coagulation and final clot strength. Mortality was reduced statistically significantly only in the animals treated with fibrinogen and rhFII or PCC, whereas administration of the combination of fibrinogen and PCC caused a fatal thromboembolic complication. The combination of fibrinogen and rhFII might be effective in reversing dilutional coagulopathy and may reduce blood loss in cases of dilutional coagulopathy.

Prothrombin complex concentrate mitigates diffuse bleeding after cardiopulmonary bypass in a porcine model

Background

Extracorporeal circuit priming and intravascular volume expansion during cardiopulmonary bypass (CPB) may lead to dilutional coagulopathy and excessive diffuse postoperative bleeding. Prothrombin complex concentrate (PCC) containing clotting factors II (FII), VII (FVII), IX (FIX), and X (FX) could be of potential value in correcting dilutional coagulopathy and reducing blood loss.

Methods

Anaesthetized pigs underwent CPB with hypothermia for 2 h at 25°C followed by 1 h of normothermia. Approximately 1 h after CPB, animals randomly received either isotonic saline 1 ml kg⁻¹ or PCC 30 IU kg⁻¹ in a volume of 1 ml kg⁻¹. Diffuse coagulopathic bleeding was assessed as suture hole blood loss from a Gore-Tex patch placed over a full-thickness incision in the left carotid artery.

Results

After CPB, levels of FII, FVII, FIX, and FX declined from baseline by 32% to 48%, and PCC fully or partially reversed those deficits. Median suture hole blood loss after administration of saline placebo was 74 ml. PCC reduced suture hole bleeding by a median of 54 ml with a 95% confidence interval of 6–112 ml (P=0.026) compared with saline. PCC, but not saline, normalized skin bleeding time. Peak thrombin generation markedly decreased after CPB, but then returned in PCC-treated animals to a level higher than baseline by 28.7 nM (14.5–41.1 nM; P=0.031).

Conclusions

PCC was effective in correcting dilutional coagulopathy and reducing diffuse bleeding in an in vivo large-animal CPB model. Further research is warranted on PCC as a haemostatic agent in CPB.

Prothrombin complex concentrate versus recombinant factor VIIa for reversal of hemodilutional coagulopathy in a porcine trauma model

BACKGROUND

Fluid resuscitation after traumatic injury may necessitate coagulation factor replacement to prevent bleeding complications of dilutional coagulopathy. Recombinant activated factor VII (rFVIIa) is being widely investigated as a hemostatic agent in trauma. Multicomponent therapy with prothrombin complex concentrate (PCC) containing coagulation factors II, VII, IX, and X might offer potential advantages.

METHODS

Anesthetized mildly hypothermic normotensive pigs were hemodiluted by substituting 65% to 70% of total blood volume in phases with hydroxyethyl starch and red cells. Thereafter, animals received 12.5 mL . kg isotonic saline placebo, 35 IU . kg PCC, or 180 microg x kg rFVIIa. Immediately afterward, a standardized spleen injury was inflicted, and prothrombin time (PT) and hemostasis were assessed. Thrombin generation was also determined.

RESULTS

Hemodilution depleted levels of factors II, VII, IX, and X markedly, prolonged PT and decreased thrombin formation. PCC and rFVIIa both fully normalized the hemodilution-induced lengthening of PT. In PCC recipients, peak thrombin generation was greater by a median of 60.7 nM (confidence interval 56.4-64.9 nM) compared with the rFVIIa group (p = 0.008). After spleen trauma, time to hemostasis was shortened to a median of 35 minutes in animals treated with PCC versus 94 minutes with rFVIIa (p = 0.016).

CONCLUSIONS

In a pilot study involving an in vivo large-animal model of spleen trauma, PCC accelerated hemostasis and augmented thrombin generation compared with rFVIIa. Further investigations are warranted on PCC as a hemostatic agent in trauma.

Reproducibility of an animal model simulating complex combat-related injury in a multiple-institution format

We developed a complex combat-relevant model of abdominal and extremity trauma, hemorrhagic shock, hypothermia, and acidosis. We then simulated injury, preoperative, and operative phases. We hypothesized that this model is reproducible and useful for randomized multicenter preclinical trials. Yorkshire swine were anesthetized, intubated, and instrumented. They then underwent femur fracture, 60% total blood volume hemorrhage, a 30-min shock period, induced hypothermia to 33 degrees C, and hemorrhage volume replacement with 3:1 isotonic sodium chloride solution (NS) at each of three centers. Hemodynamic parameters were measured continuously. Thromboelastography, arterial blood gas, and laboratory values were collected at baseline, after the shock period, and after NS replacement. Thirty-seven animals were used for model development. Eight (21%) died before completion of the study period. Twenty-nine survivors were included in the analysis. MAP (+/-SEM) after the shock period was 32 +/- 2 mmHg and was similar between centers (P = 0.4). Mean pH, base deficit, and lactate levels were 7.29 +/- 0.02, 8.20 +/- 0.65 mmol/L, and 5.29 +/- 0.44 mmol/L, respectively, after NS replacement. These were similar between centers (P > 0.05). Prothrombin time values increased significantly over time at all centers, reflecting a progressive coagulopathy (P < 0.02). Thromboelastography maximum amplitude values were similar among centers (P > 0.05) and demonstrated progressively weakened platelet interaction over time (P < 0.03). Hematocrit was similar after controlled hemorrhage (P = 0.15) and dilution (P = 0.9). The pH, lactate, base deficit, and coagulation tests reflect a severely injured state. A complex porcine model of polytrauma and shock can be used for multi-institutional study with excellent reproducibility. A consistent severe injury profile was achieved, after which experimental interventions can be applied. This is the first report of a reproducible multicenter trauma and resuscitation-related animal model.

Recombinant factor VIIa reduces rebleed hemorrhage volume in a swine aortotomy model: a randomized double-blinded study

Noncompressible hemorrhage requires hypotensive resuscitation until definitive measures can be taken to prevent rebleeding by sustaining blood pressure at subphysiological levels. Previous studies have demonstrated that a 180- or 720-microg kg(-1) dose of recombinant factor VIIa (rFVIIa) increases the MAP at which rebleeding occurs in a swine aortotomy model. The purpose of the current study was to determine the efficacy of a lower dose of 90 microg kg(-1) given prophylactically to prevent or reduce rebleeding in a prospective, randomized, blinded study using a porcine model of uncontrolled hemorrhage and resuscitation. Fourteen female 40-kg Yorkshire-cross pigs were splenectomized and instrumented with venous and arterial catheters. The infrarenal aorta was exposed, and suction catheters were placed along the right and left paracolic gutters. After a 10-min baseline, 90 microg kg(-1) (i.v.) of either rFVIIa (n = 6) or vehicle (n = 8) was administered. Five minutes later, an aortotomy was created using a 2.5-mm biopsy punch. The weight of the shed blood was continuously recorded. Lactated Ringer's was given (100 mL kg(-1) min(-1)) 10 min after aortotomy until rebleeding occurred. The MAP at rebleed and the subsequent rebleed hemorrhage volume was recorded over the 2-h study period. After rebleed occurred, lactated Ringer's sufficient to maintain MAP at baseline levels was given. Initial hemorrhage volume and rebleed MAP (P = 0.31) did not differ significantly between groups. Rebleed hemorrhage volume was reduced by 54% in the rFVIIa group from 79 +/- 4 mL kg(-1) in the vehicle group to 43 +/- 6 mL kg(-1) in the rFVIIa group (mean +/- SEM; P < 0.005). The MAP at which rebleed occurred was not different between the groups, 71 +/- 4 mmHg in the rFVIIa group versus 59 +/- 5 in the vehicle group. Prophylactic administration of rFVIIa at 90 microg kg(-1), a dose similar to the recommended dose in hemophilia patients with inhibitors, reduced rebleed hemorrhage volume, suggesting that this dose is effective in this swine aortotomy model.

Hemostatic and neuroprotective effects of human recombinant activated factor VII therapy after traumatic brain injury in pigs

Human recombinant activated factor-VII (rFVIIa) has been used successfully in the treatment of spontaneous intracerebral hemorrhage. In addition, there is increasing interest in its use to treat uncontrolled bleeding of other origins, including trauma. The aim of this study was to evaluate the safety and potential effectiveness of rFVIIa to mitigate bleeding using a clinically relevant model of traumatic brain injury (TBI) in the pig. A double injury model was chosen consisting of (1) an expanding cerebral contusion induced by the application of negative pressure to the exposed cortical surface and (2) a rapid rotational acceleration of the head to induce diffuse axonal injury (DAI). Injuries were performed on 10 anesthetized pigs. Five minutes after injury, 720 microg/kg rFVIIa (n=5) or vehicle control (n=5) was administered intravenously. Magnetic resonance imaging (MRI) studies were performed within 30 min and at 3 days post-TBI to determine the temporal expansion of the cerebral contusion. Euthanasia and histopathologic analysis were performed at day 3. This included observations for hippocampal neuronal degeneration, axonal pathology and microclot formation. The expansion of contusion volume over the 3 days post-injury period was reduced significantly in animals treated with rFVIIa compared to vehicle controls. Surprisingly, immunohistochemical analysis demonstrated that the number of dead/dying hippocampal neurons and axonal pathology was reduced substantially by rFVIIa treatment compared to vehicle. In addition, there was no difference in the extent of microthrombi between groups. rFVIIa treatment after TBI in the pig reduced expansion of hemorrhagic cerebral contusion volume without exacerbating the severity of microclot formation. Finally, rFVIIa treatment provided a surprising neuroprotective effect by reducing hippocampal neuron degeneration as well as the extent of DAI.

In vitro effect of activated recombinant factor VII (rFVIIa) on coagulation properties of human blood at hypothermic temperatures

BACKGROUND

Recombinant activated factor VII (rFVIIa) is currently administered off-label to control diffuse coagulopathic bleeding of patients with traumatic injuries. These patients are often cold, acidotic, and coagulopathic upon arrival and each responds differently to rFVIIa therapy. This study investigated the effects of hypothermia on clotting and the potential benefit of rFVIIa administration on blood coagulation at different hypothermic temperatures.

METHOD

Citrated blood samples were collected from eight healthy volunteers (20-45 years old) and incubated at 37 degrees C, 34 degrees C, 31 degrees C, and 28 degrees C for 30 minutes. rFVIIa (1.26 microg/mL equivalent to 90 microg/kg in vivo dose) or vehicle solution (saline) was added to each blood sample, incubated (10 minutes), and analyzed at the respective temperatures by standard coagulation tests and thrombelastography.

RESULTS

The clot reaction time of blood samples, measured as prothrombin time, activated partial thromboplastin time, and R time (thrombelastography analysis), was significantly prolonged at 31 degrees C or below compared with at 37 degrees C. The clot formation rate ([alpha] angle, maximum clotting velocity [Vmax]) was decreased at all cold temperatures. Maximum clot strength (maximum amplitude) was only affected (reduced) at 28 degrees C. Addition of rFVIIa shortened the prothrombin time, activated partial thromboplastin time, and R times at every temperature, surpassing the normal (37 degrees C) temperature values in 31 degrees C and 34 degrees C cold samples. Similarly, clot formation rate parameters (clotting time, [alpha] angle, Vmax) were also improved by rFVIIa addition and normothermic values were restored in 31 degrees C and 34 degrees C cold blood samples. rFVIIa did not affect maximum amplitude at any temperature.

CONCLUSIONS

Mild to moderate hypothermia delayed the initial clot reaction and reduced clot formation rate without affecting ultimate clot strength. FVIIa effectively compensated for the adverse effects of hypothermia except in severe cases. These results suggest that administration of FVIIa should be beneficial in enhancing hemostasis in hypothermic trauma patients without the need for prior correction of the patient's body temperature.

Evaluation of tris-hydroxymethylaminomethane on reversing coagulation abnormalities caused by acidosis in pigs*

OBJECTIVE

To investigate the effect of tris-hydroxymethylaminomethane (THAM) pH neutralization on reversing coagulation abnormalities caused by acidosis.

DESIGN

Random and controlled study.

SETTING

Animal research facility and laboratory.

SUBJECTS

Yorkshire swine (n = 18).

INTERVENTIONS

Acidosis was induced in 12 pigs by infusing 0.2 M hydrochloric acid (HCl). When the target pH of 7.1 was achieved, the pigs were infused with either 0.3 M THAM to achieve pH of 7.4 (intervention group) or an equal volume of lactated Ringer's solution (acid control group).

MEASUREMENTS AND MAIN RESULTS

Blood samples were taken at baseline, 15 mins after reaching pH of 7.1, and 15 mins after THAM pH neutralization. Coagulation function was assessed by thrombin generation, prothrombin time, activated partial thromboplastin time, activated clotting time, and thromboelastography (maximum clot formation time [R+K], clotting rapidity [alpha], and clot strength [maximum amplitude]). An additional six pigs (sham group) were infused with THAM, and an equal volume of fluid as the 12 coagulopathic pigs was given to assess effects of THAM and hemodilution. Comparisons were made using a mixed model analysis of variance. No change in any indexes of coagulation was observed in sham pigs. Compared with baseline, acidosis of pH 7.1 decreased base excess from 6.6 +/- 0.5 mM to -12.4 +/- 0.5 mM; reduced fibrinogen levels to 72% +/- 2%, platelet counts to 53% +/- 3%, thrombin generation to 58% +/- 4%, alpha to 84% +/- 2%, and maximum amplitude to 75% +/- 3%; and prolonged prothrombin time to 113% +/- 2%, partial thromboplastin time to 122% +/- 4%, activated clotting time to 124% +/- 3%, and R + K to 119% +/- 3% (all p < .05). THAM infusion corrected pH to 7.40 +/- 0.02 and base excess to 2.6 +/- 0.9 mM (p < .05). However, there were no differences in thrombin generation, prothrombin time, partial thromboplastin time, activated clotting time, R+K, alpha, or maximum amplitude between the groups with or without pH correction.

CONCLUSIONS

Acidosis impaired coagulation by depleting clotting factors, inhibiting thrombin generation, and affecting clot strength and stability. THAM corrected acid-base deficit but did not acutely reverse the coagulation abnormalities in the model.

Recombinant activated factor VII increases survival time in a model of incompressible arterial hemorrhage in the anesthetized pig

BACKGROUND

Hemorrhage is the leading cause of death in battlefield casualties and the second leading cause of death after civilian trauma. Evacuation time for military casualties to surgical care can be prolonged and improved hemostasis could greatly reduce mortality. There are several anecdotal reports that recombinant activated factor VII (rFVIIa) may arrest uncontrolled bleeding after trauma. However, the majority of prospective randomized controlled trials show little benefit in survival. The aim of this study was to determine whether rFVIIa could increase survival time within a clinically relevant time scale for military practice and reduce the volume of blood loss in a model of incompressible arterial hemorrhage. A secondary aim was to determine the effects of hypotensive versus normotensive resuscitation on the effectiveness of rFVIIa.

METHODS

Terminally anaesthetized Large White pigs were randomly allocated to one of four treatment groups. All animals received a controlled hemorrhage of 40% of the total estimated blood volume. They were given either rFVIIa (180 microg/kg) or placebo (saline 0.3 mL/kg) intravenously and a 4 to 5 mm longitudinal aortotomy created in the infra renal aorta before resuscitation commenced with 0.9% saline to one of two target systolic arterial blood pressures (SBPs): 110 mm Hg (normotensive) or 80 mm Hg (hypotensive). Group sizes were as follows: placebo/normotensive (6), placebo/hypotensive (7), rFVIIa/normotensive (7), and rFVIIa/hypotensive (7). Survival was monitored for a maximum of 6 hours after the onset of resuscitation.

RESULTS

rFVIIa was associated with a significantly prolonged survival time in animals managed hypotensively (214 [79-349] vs. 35 [19-52] minutes mean [95% confidence interval] rFVIIa vs. placebo, p = 0.03 Peto log rank test). There was no significant difference in survival time between those given rFVIIa and placebo in groups managed normotensively (128 [6-249] vs. 40 [15-66] minutes respectively, p = 0.27). Both rFVIIa and hypotensive management were associated with reduced uncontrolled hemorrhage volumes. There was no evidence of inappropriate intravascular thrombi or microthrombi associated with the use of rFVIIa.

CONCLUSIONS

rFVIIa, combined with hypotensive resuscitation, can increase survival time and reduce hemorrhage in a model of arterial hemorrhage. The increase in survival time is clinically relevant for military evacuation of battlefield casualties to surgical care.

Recombinant activated factor VII efficacy and safety in a model of bleeding and thrombosis in hypothermic rabbits: a blind study

BACKGROUND

Recombinant activated factor VII (rFVIIa) is increasingly used to secure hemostasis in hemorrhagic situations in trauma and surgical patients. Hypothermia is often observed in these clinical settings.

OBJECTIVE

To study the efficacy and safety of rFVIIa in hypothermia in a rabbit model of bleeding and thrombosis.

METHODS

Sixty-nine rabbits were anesthetized, ventilated and monitored for blood pressure, temperature and carotid flow. The Folts model was used: a stenosis (75%) and an injury were carried out on the carotid artery, inducing thrombosis. Blood flow decreased as thrombus size increased until the pressure gradient was such that the thrombus was released and local arterial blood flow was suddenly restored. This is known as a cyclic flow reduction (CFR). After counting baseline CFRs during a 20-min period (P1), rabbits were randomized blindly to one of four groups: normothermic (NT) placebo or rFVIIa (150 microg kg(-1)), hypothermic (HT) (34 degrees C) placebo or rFVIIa. Then CFRs were recorded over a second period (P2). At the end of the experiment, a hepato-splenic section was performed and the amount of blood loss was recorded. After each period, the following were measured: ear immersion bleeding time (BT), hemoglobin, platelet count, prothrombin time (PT), activated partial thromboplastin time (aPTT) and fibrinogen.

RESULTS

Hypothermia increased BT and blood loss. These effects were reversed by rFVIIa. In NT rabbits, rFVIIa shortened BT but did not reduce blood loss. rFVIIa-treated rabbits bled similarly regardless of temperature. The incidence of CFRs was higher in treated than placebo animals regardless of temperature. rFVIIa decreased PT and aPTT without modifying platelet count or fibrinogen level.

CONCLUSION

Hemostatic efficacy of rFVIIa was maintained in hypothermia. However, the number of CFRs was higher in the rFVIIa-treated group than in the placebo groups, whether for NT or HT rabbits.

The effects of hypothermia on fibrinogen metabolism and coagulation function in swine

Clinical coagulopathy frequently occurs in the presence of hypothermia. The primary purpose of this study was to investigate the effects of hypothermia on clotting protein fibrinogen metabolism and on coagulation function in a swine model. Twelve pigs were randomly allocated into control and hypothermia groups. Hypothermia of 32 degrees C was induced using a blanket with circulating water at 4 degrees C. Fibrinogen synthesis and breakdown were quantified using a 6-hour stable isotope infusion with subsequent gas chromatograph and mass spectrometry analysis. Clotting enzyme thrombin generation kinetics was quantified at baseline and at the end of the infusion. Changes in fibrinogen metabolism and thrombin generation were correlated with coagulation function assessed by thromboelastography (TEG). Hypothermia decreased fibrinogen synthesis from the control value of 2.6 +/- 0.4 to 1.2 +/- 0.2 mg kg(-1) h(-1) (P < .05), with no effect on fibrinogen breakdown. Thrombin generation at the initiation phase was delayed by hypothermia, but there were no changes at the propagation phase. In thromboelastography measurements, the initial clotting time (R time) was prolonged from the baseline value of 3.01 +/- 0.13 to 4.30 +/- 0.24 minutes (P < .05) and clotting rapidity (angle alpha) was decreased from the baseline value of 72.30 +/- 0.90 to 65.34 +/- 1.07 (P < .05). Hypothermia caused no significant changes in clot strength (maximum amplitude) and clot lysis (LY(60)). We concluded that hypothermia caused a potential deficit in fibrinogen availability and a delay in thrombin generation, consequently inhibiting coagulation function. Our data support the current practices of rewarming and prescribing recombinant factor VIIa for hypothermic patients with coagulation defects.

Does Bicarbonate Correct Coagulation Function Impaired by Acidosis in Swine?

BACKGROUND

Coagulopathy is an important contributor to morbidity and mortality in trauma patients. Acidosis contributes to coagulopathy. Acidosis can be neutralized with intravascular bicarbonate, but it is unclear if the coagulation defect is rapidly reversed. The effects of acidosis and bicarbonate neutralization on coagulation function were investigated in vivo.

METHODS

Acidosis was induced in 12 pigs by infusing 0.2 mol/L HCl to pH 7.1. Pigs were then infused with either LR to maintain a pH of 7.1 (A-LR, n = 6) or 0.3 mol/L bicarbonate to a pH of 7.4 (A-Bi, n = 6). Blood samples were taken at baseline, 15 minutes after acidosis induction, and 15 minutes after bicarbonate neutralization. Coagulation function was assessed by prothrombin time (PT), partial thromboplastin time (PTT), thrombin generation, initial clot formation time (R), clotting rapidity (alpha), and clot strength (MA).

RESULTS

Compared with baseline values, acidosis reduced fibrinogen concentration to 66% +/- 2% in A-LR and to 71% +/- 3% in A-Bi, and decreased platelet counts to 49% +/- 4% in A-LR and to 53% +/- 4% in A-Bi. Thrombin generation decreased to 60% +/- 4% in A-LR and to 53% +/- 7% in A-Bi. Acidosis prolonged PT and PTT about 20% and decreased alpha and MA. After pH neutralization, fibrinogen and platelet levels remained depleted and no reversal of acidosis-induced changes in thrombin generation, PT, PTT, alpha, and MA were observed.

CONCLUSION

Acidosis impaired coagulation by depleting fibrinogen and platelets and by inhibiting clotting kinetics. The deficit associated with acidosis was not reversed with bicarbonate pH neutralization.

Mechanistic implications for the use and monitoring of recombinant activated factor VII in trauma

As interest in the use of activated recombinant factor VII (rFVIIa) in trauma grows, questions arise regarding how best to monitor rFVIIa therapy and when rFVIIa may be expected to improve hemostasis. Knowledge of the mechanisms of action may be combined with available data on laboratory monitoring and efficacy in various coagulopathic states in coming to clinically relevant conclusions. This review addresses the physiology of hemostasis, placing emphasis on how rFVIIa influences the process by both tissue factor dependent and tissue factor independent mechanisms. This is extended to a mechanistic consideration of how rFVIIa may function under acidotic, hypothermic, and hemodilutional and/or consumptive conditions of trauma related coagulopathy. When these considerations are viewed alongside the available clinical data, it becomes apparent that rFVIIa has potential to improve hemostasis during trauma coagulopathy, within limitations. Common laboratory procedures are discussed with reference to mechanisms of action of rFVIIa and the available clinical data. Although there is no single assay that can predict rFVIIa efficacy in trauma, the prothrombin time (PT) is recommended as a minimum. Although a shortened PT does not predict success, correction of PT into the normal range may be a better indicator. A nonresponding PT appears to indicate that rFVIIa alone will not lead to hemostasis, and that additional blood products and other measures must be applied. Once the patient is more stable, PT and thromboelastography are recommended.

Preclinical trauma studies of recombinant factor VIIa

Preclinical studies in animals and ex vivo human blood have provided a solid rationale for conducting prospective randomized trials in trauma patients. Small animal models have been utilized to study the efficacy of recombinant activated factor VII (rFVIIa; NovoSeven) in treating thrombocytopenic rabbits and for the reversal of anticoagulation. Safety models in the rabbit also exist to test for systemic activation of clotting and pathologic thrombosis. Animal models simulating traumatic injuries in humans have primarily been performed in pigs because of species similarities in terms of coagulation characteristics and the larger internal organs. The pig studies, utilizing human rFVIIa, have shown increased strength of clot formation, decreased bleeding, and improved survival. However, these findings are not uniform and are dependant on the model chosen. All of the animal models described have provided good safety data and suggest that the use of rFVIIa is not associated with systemic activation of coagulation or microthrombosis of end organs.

Effect of Recombinant FVIIa in Hypothermic, Coagulopathic Pigs with Liver Injuries

BACKGROUND

Previous experiments with diverse pig models to evaluate the ability of rFVIIa to reduce hemorrhage have provided divergent results. The current study was conducted to address concerns related to previous work by using larger sample sizes, and an extended observational period of 4 hours post-injury. The objectives were to evaluate further the hemostatic efficacy and safety of rFVIIa administration after traumatic, uncontrolled hemorrhage.

METHODS

Anesthetized, splenectomized pigs (36.6 +/- 0.3 kg; n = 18/group) underwent an approximately 50% isovolemic blood exchange with 33 degrees C 6% hetastarch, and body temperature was adjusted to 32.5 +/- 0.5 degrees C. Subsequently, a Grade V liver injury was inflicted. After 30 seconds, either vehicle or treatment (180 microg/kg or 720 microg/kg rFVIIa) was administered intravenously as a bolus. Concomitantly, laparotomy pads were packed around the liver. Resuscitation with 33 degrees C lactated Ringer's solution (260 mL/min) was initiated and pigs were monitored for 4 hour post-injury or until death. Tissues were collected and examined histologically to assess the presence of disseminated intravascular coagulation (DIC).

RESULTS

Liver injuries were comparable among all groups (p = 0.89). Measures associated with in vitro coagulation (prothrombin time, activated partial thromboplastin time, thromboelastographic split-point and R times) were enhanced by rFVIIa administration (p < 0.05). However, neither percent survival (p = 0.82), survival time (p = 0.56), nor blood loss (p = 0.63) were affected by treatment. DIC was not evident in lung or kidney tissue.

CONCLUSIONS

These data indicate an inability of rFVIIa at these doses to reduce blood loss, or to increase survival time or percent survival in this pig model. Absence of DIC provides evidence for safe use of rFVIIa under conditions specific to this study.