Monitoring Coagulation Status For Critical Ill Patients
1Acute and Critical Care Medicine, Sapporo Higashi Tokushukai, Japan
The purpose of monitoring the coagulation status for critical illness is the early detection of both thrombosis and bleeding tendency and the assessment of the efficacy of vitamin K antagonists and direct oral anticoagulants. The platelet counts, bleeding time, prothrombin time (second, activity, ratio, international normalized ratio; INR) (PT), activated partial thromboplastin time (APTT), fibrinogen, fibrin/fibrinogen degradation products (FDP) and D-dimer are global standard markers of coagulation and fibrinolysis that are readily available worldwide and are not cumbersome to assess.
Diverse etiologies can induce thrombocytopenia due to a decreased production or increased destruction of the platelets. However, platelet counts give no information about the functional capability of the platelets. The bleeding time is independent both of coagulation and fibrinolytic factors and reflects an impaired platelet function when outside the normal range. Importantly, this is true only when the counts are above 80,000/mm3. Below this count, the bleeding time increases in parallel with the decline in the platelet counts.
PT represents extrinsic and common coagulation pathways, and APTT consists of the components of both the intrinsic and common coagulation pathways. By measuring both the PT and APTT simultaneously, we can diagnose which coagulation factors have decreased or are malfunctioning. Normal PT and prolonged APTT values suggest abnormality of Factors VIII, IX, XI and XII, which may be used to diagnose hemophilia and to detect the existence of acquired inhibitors for these factors that can induce severe bleeding.
Fibrinogen levels are critical for stopping bleeding via fibrin thrombus formation at the site of injury. It has been well recognized that in massive bleeding, the fibrinogen levels first decrease to critical levels among the various coagulation factors. Under trauma conditions, dilution, extravasation, and consumption and fibrinogenolysis due to disseminated intravascular coagulation (DIC) are the main reasons underlying decreases in the levels of fibrinogen.
FDP and D-dimer are markers of fibrin(ogen)olysis and fibrinolysis, respectively, and are fundamental components of the DIC diagnosis. Furthermore, both may be useful for diagnosing deep vein thrombosis, pulmonary thromboembolism and aortic dissection and aneurysm. DIC as well as all these conditions are important to accurately diagnose patients in critical a care setting.
Viscoelastic devices, such as thromboerastography and thromboelastometry are enthusiastically used in the North America and other Western countries. However, these approaches are not available worldwide and have not yet been recognized as standard monitoring tools in the critical care setting. The Cochrane Database failed to demonstrate evidence supporting the application of these approaches in bleeding patients to reduce the need for blood products and to improve the prognosis of the patients.
DIC, thrombotic microangiopathy, acquired inhibitors for coagulation factors, and heparin-induced thrombocytopenia are important diseases in the critical care setting. A brief summary of these conditions will be delivered if the time permits.