3 Clinical need and practice
3.1 Viscoelastometric point‑of‑care testing may be used to determine whether bleeding is a result of coagulopathy (when the blood's ability to clot is impaired) or a surgical bleed. It is mainly used in people who are having major surgery that is associated with high blood loss, such as cardiac surgery, or in people who need emergency control of bleeding caused by trauma or post‑partum haemorrhage. Viscoelastometric testing helps guide the clinician to select the most appropriate treatment to stop the bleeding.
3.2 High blood loss is associated with a marked rise in mortality in hospital. Bleeding is a potential complication of any surgical procedure, and the risk of bleeding is proportional to the size and complexity of the surgery.
3.3 The purpose of this assessment is to evaluate the clinical and cost effectiveness of viscoelastometric testing (using the ROTEM, TEG or Sonoclot systems) to detect, manage and monitor haemostasis in cardiac surgery, and in the emergency control of bleeding after trauma and during postpartum haemorrhage.
3.4 Haemostasis is the term used to describe the process of blood clotting and the subsequent dissolution of the clot after the injured tissue has been repaired. During haemostasis, 4 steps occur in a rapid sequence. First, blood vessels constrict to reduce blood loss. Second, platelets become activated by thrombin and aggregate at the site of injury, forming a temporary, loose platelet plug. The protein fibrinogen is primarily responsible for stimulating platelet clumping. Platelets clump by binding to collagen, which becomes exposed after rupture of the endothelial lining of vessels, and the plug covers the break in the vessel wall. The third step is coagulation or blood clotting. This reinforces the platelet plug with fibrin threads that act as a 'molecular glue'. Finally, the clot must dissolve for normal blood flow to resume after tissue repair. This happens through the action of plasmin. Abnormalities, in any of these 4 haemostasis steps, either acquired, or of a genetic origin, can lead to bleeding (during and after surgery) or thrombosis.
3.5 The fibrinolysis system is responsible for removing blood clots. During surgery, the body's normal process for managing clots can become severely disrupted, leading to a condition known as 'acquired hyperfibrinolysis'. Acquired hyperfibrinolysis has been observed in a variety of clinical scenarios including liver transplantation, cardiac surgery, vascular surgery, postpartum haemorrhage and severe trauma. Hyperfibrinolysis occurs when fibrinolytic activity becomes greater than fibrin formation, leading to breakdown of the clot. This results in pronounced coagulopathy and sometimes fatal bleeding.
3.6 Coagulopathy is characterised by severe bleeding in the patient. It is not easy to detect by laboratory testing because the classical coagulation tests such as prothrombin time and activated partial thromboplastin time are not sensitive for coagulopathy. However, failure to recognise and treat it can lead to uncontrollable bleeding.
3.7 For surgical procedures, mortality ranges from less than 0.1% for most routine surgery to 1% to 2% for cardiac surgery and 5% to 8% for elective vascular surgery. Mortality may be greatly increased when severe bleeding occurs during the operation.
3.8 Two population groups were included in this assessment. These were adult patients (18 years and older) having cardiac surgery, and those who need emergency control of bleeding after trauma and during postpartum haemorrhage.
3.9 Excessive bleeding (more than 2 litres) is encountered in 5% to 7% of people having cardiac surgery. If conventional methods (see section 3.15) to stop bleeding fail, reoperation (in 3.6% to 4.2% of cases) may be needed. Major blood loss is linked to adverse outcomes and associated with an 8‑fold increase in the likelihood of death. More than 30,000 people have heart surgery in the UK each year and adult cardiac surgery accounts for approximately 15% of all allogeneic red cell and allogeneic blood coagulation transfusions.
3.10 Major trauma describes serious and often multiple injuries where there is a strong possibility of death or disability. In England, the most common cause is a road traffic accident. There is an estimated minimum of 20,000 cases of major trauma each year in England resulting in 5,400 deaths. A further 28,000 cases, which may not meet the precise definition of major trauma, are cared for in the same way. People with major trauma often need complex reconstructive surgery.
3.11 Major obstetric haemorrhage occurs in approximately 6.7 per 1,000 births in the UK and is a common cause of maternal morbidity and mortality. The recognition of major obstetric haemorrhage can be challenging. Blood loss may be concealed and difficult to quantify because of dilution with amniotic fluid. Also, the physiological changes of pregnancy may mask the normal clinical signs of decrease in blood plasma volume (hypovolaemia).
3.12 There is no NICE clinical guideline on managing blood coagulation during cases of major bleeding.
3.13 Most patients who have elective surgery have normal coagulation but if their history includes any haemostatic disorders then blood coagulation and fibrinogen tests are carried out. If there is no history of abnormal bleeding, British Committee for Standards in Haematology guidelines (2008) do not recommend preoperative coagulation testing. However, some clinicians choose to order coagulation testing that includes prothrombin time, activated partial thromboplastin time, platelet count and international normalised ratio tests. These tests look at specific areas of the clotting cascade and help determine how quickly the blood will clot during some surgical procedures, such as cardiac surgery. The tests are performed on platelet‑poor plasma (blood plasma with very low number of platelets) in vitro.
3.14 During some types of elective cardiac surgery, it may be important that the blood does not clot as quickly as normal. In such cases drug treatment (such as heparin) may be given to slow the clotting time. Conversely, if the patient's blood does not clot quickly enough, drug treatment with antifibrinolytics (like tranexamic acid) and, desmopressin or allogeneic blood transfusion using platelets, fresh frozen plasma or cryoprecipitate, may be used to speed up the clotting process. Coagulation testing in most NHS hospitals takes at least 45 minutes.
3.15 To manage bleeding, early and sufficient blood product support can be given to patients with major blood loss and to those with dilutional coagulopathy. Supportive care with fresh frozen plasma and platelets can be given to patients with severe coagulopathy while the underlying condition is being treated. People with haematological disorders such as myelodysplasia or factor VIII inhibitors will need specialist care. Pharmacological agents such as prothrombin complex concentrate, fibrinogen concentrate and recombinant VIIa can be used to increase haemostatic capacity. The British Committee for Standards in Haematology guidelines on management of major haemorrhage currently state that, during major haemorrhage, prothrombin time and activated partial thromboplastin time should be maintained at less than 1.5 times baseline, platelet count should be maintained at greater than 75 times 109 platelets per litre, and fibrinogen level should be maintained at greater than 1.0 g per litre. Transfusion of fresh frozen plasma, platelet and cryoprecipitate should be considered when the levels fall below these figures.
3.16 Complications related to transfusion include transfusion‑associated graft‑versus‑host disease, administration of an incorrect blood component, haemolytic transfusion reaction, transfusion‑related acute lung injury, febrile reaction, transfusion associated circulatory overload, acute respiratory distress syndrome, multiple organ failure and infections such as HIV, hepatitis A, B and C, and malaria.
3.17 Surgical reintervention may be necessary to find out the cause of postoperative bleeding. It involves reopening the surgical site and is associated with increased morbidity and mortality. As such, it is only used after all other interventions have failed to, or are deemed unlikely to stop the bleeding.