Fibrinogen catabolism in burned patients

Tranexamic acid in burn surgery: A systematic review and meta-analysis

Burn injury causes a coagulopathy that is poorly understood. After severe burns, significant fluid losses are managed by aggressive resuscitation that can lead to hemodilution. These injuries are managed by early excision and grafting, which can cause significant bleeding and further decrease blood cell concentration. Tranexamic acid (TXA) is an anti-fibrinolytic that has been shown to reduce surgical blood losses; however, its use in burn surgery is not well established. We performed a systematic review and meta-analysis to investigate the influence TXA may have on burn surgery outcomes. Eight papers were included, with outcomes considered in a random-effects model meta-analysis. Overall, when compared to the control group, TXA significantly reduced total volume blood loss (mean difference (MD) = -192.44; 95% confidence interval (CI) = -297.73 to - 87.14; P = 0.0003), the ratio of blood loss to burn injury total body surface area (TBSA) (MD = -7.31; 95% CI = -10.77 to -3.84; P 0.0001), blood loss per unit area treated (MD = -0.59; 95% CI = -0.97 to -0.20; P = 0.003), and the number of patients receiving a transfusion intraoperatively (risk difference (RD) = -0.16; 95% CI = -0.32 to - 0.01; P = 0.04). Additionally, there were no noticeable differences in venous thromboembolism (VTE) events (RD = 0.00; 95% CI = -0.03 to 0.03; P = 0.98) and mortality (RD = 0.00; 95% CI = -0.03 to 0.04; P = 0.86). In conclusion, TXA can potentially be a pharmacologic intervention that reduces blood losses and transfusions in burn surgery without increasing the risk of VTE events or mortality.

Burn-Induced Coagulopathies: a Comprehensive Review

Burn-induced coagulopathy is not well understood, and consensus on diagnosis, prevention, and treatments are lacking. In this review, literature on burn-induced (and associated) coagulopathy is presented along with the current understanding of the effects of burn injury on the interactions among coagulation, fibrinolysis, and inflammation in the acute resuscitative phase and reconstructive phase of care. The role of conventional tests of coagulopathy and functional assays like thromboelastography or thromboelastometry will also be discussed. Finally, reported methods for the prevention and treatment of complications related to burn-induced coagulopathy will be reviewed.

Venous Thromboembolism Chemoprophylaxis in Burn Patients: A Literature Review and Single-Institution Experience

Hospitalized burn patients meet the criteria for Virchow's triad (endothelial damage, hypercoagulability, and stasis), predisposing them to venous thromboembolism (VTE). Although the disease burden of VTE suggests a need for prevention in this population, unreliable reported VTE rates, costly and complicated prophylaxis regimens, and chemoprophylaxis risks have prevented the establishment of a universal protocol. This paper reviews thromboprophylaxis practices both in the literature and at our own institution. A systematic review was conducted according to PRISMA guidelines identifying studies pertaining to VTE chemoprophylaxis in burn patients. Additionally, medical records of patients admitted to an American Burn Association-verified burn center between June 2015 and June 2019 were retrospectively reviewed for demographics, chemoprophylaxis, and presence of VTE defined as either deep vein thrombosis (DVT) or pulmonary embolism (PE). Thirty-eight studies met inclusion criteria. In the 12 studies that reported VTE incidence, rates ranged widely from 0.25% to 47.1%. The two largest retrospective studies (n = 33,637 and 36,638) reported a VTE incidence of 0.61% and 0.8% in populations with unknown or inconsistently recorded chemoprophylaxis. Throughout the literature, prevention protocols were mixed, though a trend toward using dose-adjusted subcutaneous low molecular weight heparin based on serum anti-factor Xa level was noted. At our burn center, 1,068 patients met study criteria. At-risk patients received a simple chemoprophylaxis regimen of 5000U of subcutaneous unfractionated heparin every 8 hours. No routine monitoring tests were performed to limit cost. Nine cases of DVT and two cases of PE were identified with an incidence of 0.84% and 0.19%, respectively, and a total VTE incidence of 1.03%. Only one patient developed heparin-induced thrombocytopenia (HIT). No cases of other heparin-associated complications were observed. VTE incidence rates reported in the literature are wide-ranging and poorly capture the effect of any one chemoprophylaxis regimen in the burn population. Our center uses a single, safe, and cost-effective protocol effecting a low VTE rate comparable to that of large national retrospective studies.

Role of Elevated Fibrinogen in Burn-Induced Mitochondrial Dysfunction: Protective Effects of Glycyrrhizin

INTRODUCTION

Skeletal muscle wasting and weakness with mitochondrial dysfunction (MD) are major pathological problems in burn injury (BI) patients. Fibrinogen levels elevated in plasma is an accepted risk factor for poor prognosis in many human diseases, and is also designated one of damage-associated molecular pattern (DAMPs) proteins. The roles of upregulated fibrinogen on muscle changes of critical illness including BI are unknown. The hypothesis tested was that BI-upregulated fibrinogen plays a pivotal role in the inflammatory responses and MD in muscles, and that DAMPs inhibitor, glycyrrhizin mitigates the muscle changes.

METHODS

After third degree BI to mice, fibrinogen levels in the plasma and at skeletal muscles were compared between BI and sham-burn (SB) mice. Fibrinogen effects on inflammatory responses and mitochondrial membrane potential (MMP) loss were analyzed in C2C12 myotubes. In addition to survival, the anti-inflammatory and mitochondrial protective effects of glycyrrhizin were tested using in vivo microscopy of skeletal muscles of BI and SB mice.

RESULTS

Fibrinogen in plasma and its extravasation to muscles significantly increased in BI versus SB mice. Fibrinogen applied to myotubes evoked inflammatory responses (increased MCP-1 and TNF-α; 32.6 and 3.9-fold, respectively) and reduced MMP; these changes were ameliorated by glycyrrhizin treatment. In vivo MMP loss and superoxide production in skeletal muscles of BI mice were significantly attenuated by glycyrrhizin treatment, together with improvement of BI survival rate.

CONCLUSIONS

Inflammatory responses and MMP loss in myotubes induced by fibrinogen were reversed by glycyrrhizin. Anti-inflammatory and mitochondrial protective effect of glycyrrhizin in vivo leads to amelioration of muscle MD and improvement of BI survival rate.

Coagulopathy and its management in patients with severe burns

Severe burn injury is associated with systemic coagulopathy. The changes in coagulation described in patients with severe burns resemble those found patients with sepsis or major trauma. Coagulopathy in patients with severe burns is characterized by procoagulant changes, and impaired fibrinolytic and natural anticoagulation systems. Both the timing of onset and the severity of hemostatic derangements are related to the severity of the burn. The exact pathophysiology and time course of coagulopathy are uncertain, but, at least in part, result from hemodilution and hypothermia. As the occurrence of coagulopathy in patients with severe burns is associated with increased comorbidity and mortality, coagulopathy could be seen as a potential therapeutic target. Clear guidelines for the treatment of coagulopathy in patients with severe burns are lacking, but supportive measures and targeted treatments have been proposed. Supportive measures are aimed at avoiding preventable triggers such as tissue hypoperfusion caused by shock, or hemodilution and hypothermia following the usually aggressive fluid resuscitation in these patients. Suggested targeted treatments that could benefit patients with severe burns include systemic treatment with anticoagulants, but sufficient randomized controlled trial evidence is lacking.

Early coagulopathy of major burns

INTRODUCTION AND AIMS

The pathophysiology and time-course of coagulopathy post major burns are inadequately understood. The aims of this study were to review the incidence of acute coagulopathy post major burns, potential contributing factors associated with this coagulopathy and outcome of patients who developed early coagulopathy.

METHODS

A retrospective review of all patients with major burns (≥20% total body surface area (TBSA)) presenting to a tertiary burns referral centre was conducted. Data on demographic, injury characteristics and fluid resuscitation practices were recorded and tested for association with coagulopathy (INR>1.5 or aPTT>60 s) at hospital presentation and within 24 h of burns injury. Mortality, intensive care unit (ICU) admission, mechanical ventilation and blood and blood product usage were primary endpoints.

RESULTS

There were 99 patients who met the inclusion criteria with 36 (16) %TBSA burns. Coagulopathy was present in only three patients on presentation, but 37 (37%) patients developed early onset (within 24 h of injury) coagulopathy. Early onset coagulopathy was independently associated with %TBSA burnt (p<0.001) and volume of fluid administered (p=0.005). Early onset coagulopathy was associated with higher volumes of blood and blood product administration, ICU admission and prolonged mechanical ventilation.

CONCLUSIONS

Post major burns, a very low proportion of patients presented with coagulopathy, but a substantial proportion of patients developed coagulopathy within 24 h. This and the association of coagulopathy with the volume of fluid resuscitation suggest dilution as a major cause of the early coagulopathy of major burns.

Thromboelastography as a better indicator of hypercoagulable state after injury than prothrombin time or activated partial thromboplastin time

OBJECTIVES

To investigate the hemostatic status of critically ill, nonbleeding trauma patients. We hypothesized that a hypercoagulable state exists in patients early after severe injury and that the pattern of clotting and fibrinolysis are similar between burned and nonburn trauma patients.

MATERIALS

Patients admitted to the surgical or burn intensive care unit within 24 hours after injury were enrolled. Blood samples were drawn on days 0 through 7. Laboratory tests included prothrombin time (PT), activated partial thromboplastin time (aPTT), levels of activated factor XI, D-dimer, protein C percent activity, antithrombin III percent activity, and thromboelastography (TEG).

RESULTS

Study subjects were enrolled from April 1, 2004, to May 31, 2005, and included nonburn trauma patients (n = 33), burned patients (n = 25), and healthy (control) subjects (n = 20). Despite aggressive thromboprophylaxis, three subjects (2 burned and 1 nonburn trauma patients [6%]) had pulmonary embolism during hospitalization. Compared with controls, all patients had prolonged PT and aPTT (p < 0.05). The rate of clot formation (alpha angle) and maximal clot strength were higher for patients compared with those of controls (p < 0.05), indicating a hypercoagulable state. Injured patients also had lower protein C and antithrombin III percent activities and higher fibrinogen levels (p < 0.05 for all). Activated factor XI was elevated in 38% of patients (control subjects had undetectable levels).

DISCUSSION

Thromboelastography analysis of whole blood showed that patients were in a hypercoagulable state; this was not detected by plasma PT or aPTT. The high incidence of pulmonary embolism indicated that our current prophylaxis regimen could be improved.

Degree of hypercoagulability and hyperfibrinolysis is related to organ failure and prognosis after burn trauma

Severely burned patients often present a hypercoagulability situation. However, its magnitude, time course, and relationship with organ failure and outcome remains to be established. Forty-three patients were studied on the first and seventh day after burn for hypercoagulability and fibrinolysis parameters. A hypercoagulability and hyperfibrinolysis state was found the first day after burn demonstrated by high levels of activated factor VII (VIIa, p<0.01), thrombin-antithrombin III complex (TAT, p<0.01), tissue plasminogen activator (t-PA, p<0.001) and D dimer (DD, p<0.01) and low levels of antithrombin III (ATIII, p<0.01), protein C (PC, p<0.01), plasminogen (PG, p<0.001) and alpha2 antiplasmin (AP, p<0.001). A paradoxical coexisting hypofibrinolysis was found as suggested by a low global fibrinolytic activity in the euglobulin plasma fraction fibrin plate assay (FA, p<0.01) and high levels of tissue plasminogen activator inhibitor type 1 (PAI-1, p<0.01). On day 7, a less marked hypercoagulability situation was found, with low ATIII (p<0.01) and PC (p<0.01), persisting the hypofibrinolytic situation observed on the first day. Non-survivors (NS) showed higher levels of VIIa (p<0.01), TAT (p<0.05) and t-PA (p<0.05), and lower levels of ATIII (p<0.05), PC (p<0.05) and AP (p<0.001) than survivors (S) on the first day. Also, there was a positive correlation of Marshall organ failure score with ATIII, (r2=0.49, p<0.001), PC, (r2=0.14, p<0.045) and PG levels, (r2=0.41, p<0.0003). Severely burned patients show a state of transient disseminated intravascular coagulation, related to the development of organ failure and outcome.

Is there a need for antithrombin III substitution early after burn injury?

The changes in antithrombin III (AT-III) levels in the blood and restitution in coagulation parameters between patients receiving and not receiving AT-III substitution were examined early after burn injury. The study was divided into two parts with a total of 14 consecutive patients (per cent total body surface area (TBSA) > or = 20 per cent). The first six patients were given AT-III substitution when AT-III levels fell below 50 per cent. The second part examined the restitution of the coagulation parameters when the patients (n = 8) obtained AT-III substitution only at extremely low values of AT-III. The decline in AT-III observed occurred in parallel to the permeability changes and the haemodilution normally seen secondarily to the initial fluid rescucitation. The observed changes in the coagulation parameters were modest and no hepatic dysfunction was noted. In addition, no differences of the restitution in these coagulation parameters were noted between the substituted and non-substituted groups. These results suggest that changes in AT-III early after burn injury depend mainly on factors other than an ongoing disseminated coagulation process. Probable causes are increased capillary leak and haemodilution. Our results suggest that substitution of AT-III in the early postburn period, on the assumption that low levels alone indicate ongoing coagulation, is not warranted.

An investigation of the role of diet and burn injury on wound healing

Forty-four rats underwent standard laparotomies and were randomly allocated to four groups according to injury (control or burned) and diet (maintenance or protein depleted). Wound healing was assessed tensiometrically on the 14th postoperative day. The energy intakes of the four groups were comparable. Both injury by burning and protein depletion caused significant weight loss. The peak force applied to the laparotomy wounds was unaltered by burning, but protein depletion caused a significant reduction in wound strength. It is concluded that any impairment in wound healing in burned patients is more likely to result from inadequate feeding rather than the injury itself or any resultant weight loss.

Anticoagulation therapy for renal insufficiency after burns

The changes in blood coagulation, fibrinolysis and kidney function and the effect of anticoagulation therapy using herapin were investigated in rabbits with full thickness skin loss burns covering 35 per cent of the total body surface area. Determinations of various kidney function tests, blood coagulation and fibrinolysis tests, blood viscosity and haematocrit values were made before burning and after 8 and 24h. Thirty rabbits were divided into a non-therapy group, an intravenous infusion group, a heparin group, an antithrombin III group and an antithrombin III plus heparin group and the results were compared. Oliguria and a disturbance of kidney function were noted 8 h after the burn in the non-therapy group. In the intravenous infusion group urine volume was well maintained although the early stage of non-oliguric renal insufficiency was noted. The changes noted in the intravenous infusion group were prevented almost completely in the heparin group but FENa and CH2O were elevated at 24h probably because antithrombin III activity was markedly depressed. In the antithrombin III group and the antithrombin III plus heparin group, however, creatinine clearance (Clcr) was moderately elevated while FENa and CH2O remained unchanged as compared with the values before the burn. The antithrombin III plus heparin group showed slightly better results than the antithrombin III group in Ucr/Pcr ratio, Clcr and CH2O. The results of the present study indicate that it is extremely effective to initiate appropriate fluid therapy immediately after a burn and to administer antithrombin III concentrate in combination with or without heparin for the prevention of acute renal insufficiency in patients with a severe burn.

Formation of soluble fibrin oligomers in purified systems and in plasma

The kinetic parameters for release of fibrinopeptide A (FPA) from human fibrinogen by thrombin are: Km = 2.3 X 10(-6)M and Vmax. = 1.1 X 10(-10)mol of FPA/s per unit of thrombin; for fibrin formation, Km is similar to that for FPA release, but, the conditions of the present study, Vmax. was approximately half of that for FPA release. The formation of fibrin polymer before the sol-gel transition was studied by gel-permeation chromatography combined with effluent analysis for fibrinogen antigen and residual FPA. Polymer formation in purified fibrinogen incubated with thrombin proceeded as a bimolecular association of exposed sites in a manner predicted by probability calculations and assuming random FPA cleavage. Each oligomer consisted of n molecules of fibrin monomer and two fibrinogen molecules, each of the latter lacking one FPA molecule, i.e. each oligomer, regardless of molecular size, retains two FPA molecules. The addition of 5 mM-CaCl2 to the reaction mixture changed the rate of polymer formation, so that dimer was no longer the prevalent oligomer; in the presence of Ca2+, the trimer was the oligomer in highest concentration. The polymers formed in the presence of calcium were similar in composition to those without, i.e. 2 mol of FPA/mol of oligomer. EDTA-treated plasma samples incubated for short periods of time, 30s or less, with thrombin ranging in concentration up to 1 N.I.H. unit/ml did not form clots during the 10-15 min period of observation until they were applied to the column, though a large proportion of the available FPA was cleaved (maximum 45%). The soluble polymers in plasma were mostly of the high-Mr variety (tetramer and greater); these high-Mr polymers contained less than 2 mol of FPA/mol of polymer, whereas dimer and trimer in plasma were similar to those in the purified systems, i.e. 2 mol of FPA/mol.