Hemostatic drugs

Redo cardiac surgery in a Jehovah's Witness, the importance of a multidisciplinary approach to blood conservation

Although Jehovah's Witnesses present a particular problem when undergoing surgery because of their refusal to accept stored blood, it is now quite common to undertake uncomplicated cardiac surgery in these patients. Complex or redo cardiac surgery however, is often associated with major blood loss, and is conventionally contraindicated in Jehovah's Witnesses. We describe the perioperative management of a Jehovah's Witness who underwent a resternotomy for mitral valve replacement and coronary artery bypass grafting having previously had an aortic valve replacement and mitral valve repair. The importance of a multidisciplinary approach to blood conservation is discussed.

Severe hyponatraemia secondary to desmopressin therapy in von Willebrand's disease

A 42-year-old female with von Willebrand's disease was managed with desmopressin and tranexamic acid to aid haemostasis following a vaginal hysterectomy. Severe acute hyponatraemia (134 to 108 mmol/l) developed over two days, culminating in a generalized tonic-clonic seizure and cerebral oedema. Fluid restriction, cessation of desmopressin and hypertonic saline administration led to a full recovery. Desmopressin is known to reduce free water elimination and produce hyponatraemia, but its extent and rate of development in this patient was surprising. Close monitoring of serum sodium and fluid balance is recommended in these patients.

Hematologic management of gastrointestinal bleeding

The hematologic management of gastrointestinal (GI) bleeding requires evaluation of the underlying cause of bleeding, associated diseases that can exacerbate the bleeding, and identification of related and unrelated coagulation abnormalities. Erythrocyte transfusions are given to increase oxygen carrying capacity; however, there is limited information on the level of anemia that places a patient at increased risk of adverse events after a GI bleed and when patients should receive erythrocyte transfusion. Isolated thrombocytopenia is uncommon in patients with GI bleeding, and there is little evidence documenting the degree of thrombocytopenia associated with an increased risk of bleeding. Platelets are often administered when the count is 50,000 per cu/mL in a bleeding patient. The coagulopathy of liver disease is the most common abnormality seen in the setting of GI bleeding. Fresh-frozen plasma (FFP) should be given in a dose equivalent to the underlying abnormality and the common practice of administering 2 units of FFP is often insufficient in a bleeding patient.

Improved purification of the membrane-bound hydrogenase-sulfur-reductase complex from thermophilic archaea using epsilon-aminocaproic acid-containing chromatography buffers

A hydrogenase-sulfur reductase (SR) complex was purified from membrane preparations of the extremely thermophilic, acidophilic archaeon Acidianus ambivalens using a combination of sucrose density gradient centrifugation and column chromatography (FPLC). All chromatographic steps were performed in the presence of 0.5% epsilon-aminocaproic acid resulting in the elution of the SR complex as a sharp peak. In contrast, chromatography using buffers without epsilon-aminocaproic acid, or in the presence of detergents, were not successful. The purified A. ambivalens SR complex consisted of at least four subunits with relative molecular masses of 110000, 66000, 39000 and 29000, respectively. A similar procedure was applied to purify the membrane-bound hydrogenase from Thermoproteus neutrophilus, a non-related extremely thermophilic but neutrophilic archaeon, which consisted of only two subunits with relative molecular masses of 66000 and 39000, respectively.

Pharmacological strategies to decrease excessive blood loss in cardiac surgery: a meta-analysis of clinically relevant endpoints

BACKGROUND

Excessive bleeding may complicate cardiac surgery, and is associated with increased morbidity and mortality. Pharmacological strategies to decrease perioperative bleeding have been investigated in a large number of controlled trials, most of which have shown a decrease in blood loss. However, most studies lacked sufficient power to detect a beneficial effect on clinically more relevant outcomes. We did a meta-analysis of all randomised, controlled trials of the three most frequently used pharmacological strategies to decrease perioperative blood loss (aprotinin, lysine analogues [aminocaproic acid and tranexamic acid], and desmopressin).

METHODS

Studies were included if they reported at least one clinically relevant outcome (mortality, rethoracotomy, proportion of patients receiving a transfusion, or perioperative myocardial infarction) in addition to perioperative blood loss. In addition, a separate meta-analysis was done for studies concerning complicated cardiac surgery.

FINDINGS

We identified 72 trials (8409 patients) that met the inclusion criteria. Treatment with aprotinin decreased mortality almost two-fold (odds ratio 0.55 [95% CI 0.34-0.90]) compared with placebo. Treatment with aprotinin and with lysine analogues decreased the frequency of surgical re-exploration (0.37 [0.25-0.55], and 0.44 [0.22-0.90], respectively). These two treatments also significantly decreased the proportion of patients receiving any allogeneic blood transfusion. By contrast, the use of desmopressin resulted in a small decrease in perioperative blood loss, but was not associated with a beneficial effect on other clinical outcomes. Aprotinin and lysine analogues did not increase the risk of perioperative myocardial infarction; however, desmopressin was associated with a 2.4-fold increase in the risk of this complication. Studies in patients undergoing complicated cardiac surgery showed similar results.

INTERPRETATION

Pharmacological strategies that decrease perioperative blood loss in cardiac surgery, in particular aprotinin and lysine analogues, also decrease mortality, the need for rethoracotomy, and the proportion of patients receiving a blood transfusion.

Management of bleeding with uremia and liver disease

Bleeding can complicate the clinical course of both liver disease and uremia. The pathogenesis of bleeding in both syndromes is complex. A variety of options are available for treatment of uremic bleeding including desmopressin, erythropoietin, and estrogens. Bleeding complications of liver disease reflect the importance of this organ for the production of both coagulation factors and thrombopoietin. Careful assessment of both the patient's clinical situation and laboratory findings is important for tailoring therapy of the bleeding patient.

Tranexamic acid: a review of its use in surgery and other indications

Tranexamic acid is a synthetic derivative of the amino acid lysine that exerts its antifibrinolytic effect through the reversible blockade of lysine binding sites on plasminogen molecules. Intravenously administered tranexamic acid (most commonly 10 mg/kg followed by infusion of 1 mg/kg/hour) caused reductions relative to placebo of 29 to 54% in postoperative blood losses in patients undergoing cardiac surgery with cardiopulmonary bypass (CPB), with statistically significant reductions in transfusion requirements in some studies. Tranexamic acid had similar efficacy to aprotinin 2 x 10(6) kallikrein inhibitory units (KIU) and was superior to dipyridamole in the reduction of postoperative blood losses. Transfusion requirements were reduced significantly by 43% with tranexamic acid and by 60% with aprotinin in 1 study. Meta-analysis of 60 trials showed tranexamic acid and aprotinin, unlike epsilon-aminocaproic acid (EACA) and desmopressin, to reduce significantly the number of patients requiring allogeneic blood transfusions after cardiac surgery with CPB. Tranexamic acid was associated with reductions relative to placebo in mortality of 5 to 54% in patients with upper gastrointestinal bleeding. Meta-analysis indicated a reduction of 40%. Reductions of 34 to 57.9% versus placebo or control in mean menstrual blood loss occurred during tranexamic acid therapy in women with menorrhagia; the drug has also been used to good effect in placental bleeding, postpartum haemorrhage and conisation of the cervix. Tranexamic acid significantly reduced mean blood losses after oral surgery in patients with haemophilia and was effective as a mouthwash in dental patients receiving oral anticoagulants. Reductions in blood loss were also obtained with the use of the drug in patients undergoing orthotopic liver transplantation or transurethral prostatic surgery, and rates of rebleeding were reduced in patients with traumatic hyphaema. Clinical benefit has also been reported with tranexamic acid in patients with hereditary angioneurotic oedema. Tranexamic acid is well tolerated; nausea and diarrhoea are the most common adverse events. Increased risk of thrombosis with the drug has not been demonstrated in clinical trials.

CONCLUSIONS

Tranexamic acid is useful in a wide range of haemorrhagic conditions. The drug reduces postoperative blood losses and transfusion requirements in a number of types of surgery, with potential cost and tolerability advantages over aprotinin, and appears to reduce rates of mortality and urgent surgery in patients with upper gastrointestinal haemorrhage. Tranexamic acid reduces menstrual blood loss and is a possible alternative to surgery in menorrhagia, and has been used successfully to control bleeding in pregnancy.

Acute hyperkalemia associated with intravenous epsilon-aminocaproic acid therapy

Epsilon-aminocaproic acid (Amicar) is used to treat severe hemorrhage refractory to usual medical management. This antifibrinolytic drug has been associated with a number of renal complications. However, there are no descriptions of this medication causing hyperkalemia. This report describes the development of hyperkalemia in a patient with underlying chronic renal insufficiency treated with intravenous epsilon-aminocaproic acid. The patient, who underwent coronary artery bypass grafting, had no other obvious cause for the acute increase in serum potassium concentration. Based on data in animals and humans, the cationic amino acids lysine and arginine have been shown to enter muscle cells in exchange for potassium and lead to hyperkalemia through a shift of potassium from the intracellular to the extracellular space. Epsilon-aminocaproic acid, a synthetic amino acid structurally similar to lysine and arginine, also has been noted to cause an acute increase in serum potassium in anephric dogs infused with this medication. It is probable that the mechanism underlying the increase in serum potassium with epsilon-aminocaproic acid is also based on the shift of potassium from the intracellular to the extracellular space. Hence, it appears that intravenous epsilon-aminocaproic acid can also cause hyperkalemia in humans.

Comparison of the effects of transfusions of cryopreserved and liquid-preserved platelets on hemostasis and blood loss after cardiopulmonary bypass

OBJECTIVE

The aim of the study was to compare the clinical effects and hemostatic efficiency of transfusions of platelets preserved in the frozen state for as long as 2 years with transfusions of platelets preserved in the conventional manner for as long as 5 days in patients undergoing cardiopulmonary bypass.

METHODS

Seventy-three patients were prospectively randomly assigned to receive transfusions of cryopreserved or liquid-preserved platelets. Nonsurgical blood loss was measured during and after the operation. Bleeding time, hematologic variables, and the bleeding time site shed blood were assayed before cardiopulmonary bypass and at 30 minutes and 2, 4, and 24 hours after transfusion. In vitro platelet function tests were conducted on platelets obtained from healthy volunteers.

RESULTS

No adverse sequelae of the transfusions were observed. Blood loss and the need for postoperative blood product transfusions were lower in the group receiving cryopreserved platelets. Lower posttransfusion platelet increments and a tendency toward decreased platelet survival were observed in patients receiving cryopreserved platelets. Hematocrit and plasma fibrinogen were significantly higher in this group, and the duration of intubation was shorter. In vitro, cryopreserved platelets demonstrated less aggregation, lower pH, and decreased response to hypotonic stress but generated more procoagulant activity and thromboxane.

CONCLUSIONS

(1) Cryopreserved platelet transfusions are superior to liquid-preserved platelets in reducing blood loss and the need for blood product transfusions after cardiopulmonary bypass. (2) The reduction in blood loss in the patients receiving cryopreserved platelet transfusions after cardiopulmonary bypass probably reflects improved in vivo hemostatic function of cryopreserved platelets. (3) Some in vitro measures of platelet quality (aggregation, pH, hypotonic stress) may not reflect in vivo quality of platelet transfusions after cardiopulmonary bypass, whereas other in vitro measures (platelet procoagulant activity and thromboxane) do.

Treatment of von Willebrand Disease

The general goal of therapy in von Willebrand disease is to correct the two defects that are related to the bleeding tendency of these patients, i.e., the abnormal primary hemostasis expressed by a prolonged bleeding time (BT) and the abnormal intrinsic coagulation due to low factor VIII (FVIII) levels. There are two main treatments in von Willebrand disease, i.e., desmopressin and transfusional therapy with blood products. Desmopressin is most effective in patients with type 1, who account for about 80 per cent of all patients. The remaining patients with type 2 and type 3 von Willebrand disease do not respond consistently to desmopressin and need the infusion of blood products containing FVIII and von Willebrand factor. Virally-inactivated concentrates that are currently on the market are preferable to fresh-frozen plasma and cryoprecipate, that still carry a small risk of transmitting blood-borne infections. In rare instance, particularly for hemorrhoages in mucosal tracts such as gastrointestinal bleeding, platelet concentrates are useful adjuncts to plasma concentrates when patients do not respond to the latters. The role of purified von Willebrand factor and of recombinant products is still unclear.