Blood clots affect 30 000 Australians every year. They are potentially fatal if left untreated and account for about 10% of hospital deaths (ACSQHC 2018; Healthdirect 2019a).
As a healthcare professional, being able to recognise and manage blood clots is an essential skill that may save a patient’s life.
Note: While this article is a general overview of blood clots, it will mainly focus on VTE (DVT and PE).
What is a Blood Clot?
A blood clot is a semisolid mass of blood components (platelets, proteins and cells) that clumps together in a process known as coagulation (i.e. the clotting mechanism) (Axtell & Murrell 2018).
The blood components that form clots are referred to as ‘clotting factors’ (Cancer.Net 2019).
Blood is essential for life as it delivers oxygen to the tissues and cells, and a significant loss of blood may be fatal. Coagulation, a component of haemostasis, is the body’s crucial mechanism to prevent significant blood loss when we are injured (Garmo, Bajwa & Burns 2020; Moake 2020).
Coagulation works by forming a clot to plug the blood vessel wall injury. Once the injured blood vessel has healed, the clot will generally dissolve on its own (Garmo, Bajwa & Burns 2020; Moake 2020).
What is the Clotting Cascade?
The clotting cascade is a sequence of actions that occur upon the injury of a blood vessel in order to rapidly achieve haemostasis. It causes clotting factors to activate one after the other like a waterfall, resulting in the creation of a blood clot to plug the injury site until it has healed (Lab Tests Online 2021; Chaudhry, Usama & Babiker 2020).
There are two stages of the clotting cascade:
Primary haemostasis, where a weak platelet plug is formed in order to temporarily prevent haemorrhage until stability can be achieved through secondary haemostasis. It comprises four phases: vasoconstriction, platelet adhesion, platelet activation, and platelet aggregation.
Secondary haemostasis triggers the clotting cascade in order to stabilise the weak platelet plug that has been formed. There are two possible pathways for the cascade - intrinsic and extrinsic - both of which meet at the common pathway to finish the process.
(Garmo, Bajwa & Burns 2020)
The intrinsic and extrinsic pathways have different triggers (Reading 2018).
The extrinsic pathway is the shorter and more dominant of the two pathways (Chaudhry, Usama & Babiker 2020; Reading 2018). It is activated in response to:
While haemostasis is an essential physiological process, there is a delicate balance that must be maintained between clotting factors that promote bleeding and those that promote coagulation (Cancer.Net 2019).
If there is too much bleeding, the individual is at risk of losing excessive blood from a minor injury. On the other hand, if there is too much clotting, uninjured blood vessels can become plugged. Any abnormality in haemostasis may disrupt this balance, with potentially dangerous consequences (Moake 2020).
If the clotting factors that promote coagulation are missing or damaged, there is a risk that the body will form blood clots that block normal blood flow (Cancer.Net 2019).
Types of Blood Clots
Note: A thrombus is a blood clot that forms in a vein or artery (Healthdirect 2020).
DVT occurs when a thrombus forms in a deep vein. This can occur anywhere in the body but is most common in the lower leg, thigh, pelvis or arm (CDC 2020). The most common symptoms are pain and swelling in the affected area. In some cases, a DVT will dissolve on its own (Healthdirect 2019a; ACSQHC 2020).
PE is a complication of DVT that occurs when the thrombus partially or completely dislodges and travels to the lungs. This is a serious and potentially life-threatening complication (ACSQHC 2020; Healthdirect 2019a).
Blood clot in a vein near the skin (superficial thrombosis).
(Healthdirect 2019a; 2020)
What is Virchow’s Triad?
Virchow’s triad describes the three primary risk factor categories for venous thromboembolism:
Hypercoagulability (blood disorders that increase the risk of clotting), for example, an inherited Factor V Leiden mutation
Abnormal blood flow, for example, stasis due to obesity or immobility
Vessel wall injury (aka endothelial Injury), for example, damage from smoking or sepsis.
(Garmo, Bajwa & Burns 2020; Kushner, West & Pillarisetty 2020)
Risk Factors for Blood Clots
Specific risk factors include:
Older age (over 65), partially due to increased risk of comorbidity
Immobility due to prolonged travel (e.g. long-haul flights), prolonged surgery, post-surgical immobilisation or trauma
Surgery (particularly major orthopedic and neurovascular surgeries)
Previous blood clot
Pregnancy (particularly during the postpartum period), which causes a hypercoagulable state (increased risk for women with multiple pregnancies and women of a late maternal age)
Cancer (which is associated with hypercoagulability), particularly pancreatic, ovarian, stomach, renal, adenocarcinoma, glioblastoma, metastatic melanoma, lymphoma and advanced breast cancers; acute leukemias; and myeloma