Junior Doctor Tips - Anticoagulation & VTE Prophylaxis
As Junior Doctors, you will frequently encounter patients who require anticoagulation therapy and venous thromboembolism (VTE) prophylaxis. Conditions such as unstable angina, heart attacks, deep venous thrombosis, and pulmonary embolisms necessitate careful management, and understanding the protocols and considerations surrounding these treatments is essential for optimal patient outcomes. In this blog post, we will delve into the key aspects of anticoagulation and VTE prophylaxis and discuss the various therapies, monitoring methods, potential side effects, and risk assessment guidelines.
Venous Thromboembolism (VTE) Prophylaxis: A Crucial Strategy
Venous thromboembolism (VTE) prophylaxis is a critical strategy that involves both pharmacological and non-pharmacological measures aimed at reducing the risk of deep vein thrombosis (DVT) and pulmonary embolism (PE). A DVT occurs when blood clot (or clots) develop in the major deep veins of the leg or thigh, leading to painful swelling. A PE is a consequence of thrombus migration to the pulmonary vasculature, often originating from distal veins in the lower extremities. In fact, approximately 51% of deep venous thrombi eventually embolise to the pulmonary vasculature, resulting in a PE.
The US Agency for Healthcare Research and Quality (AHRQ) identifies thromboprophylaxis as the top patient safety strategy for hospitalised patients as they are particularly susceptible to VTE for several reasons, namely disease burden and immobilisation. VTE remains one of the most common and preventable complications associated with hospital admission; as rates of asymptomatic hospital-acquired DVT range from 10% to 60% without thromboprophylaxis, the importance of effective prevention cannot be overstated. Furthermore, PE stands as a leading cause of preventable in-hospital mortality both in the USA as well as in Europe.
Postoperative VTE has also been identified as a significant contributor to extended hospital stays. Treating PE or DVT typically requires a minimum of 3 months of anticoagulation, which comes with a substantial bleeding risk. Even with proper anticoagulation, patients may experience long-term complications, such as chronic pulmonary hypertension (occurs in ~3% of PE patients) and post-thrombotic syndrome (occurs in ~20%-50% of DVT patients).
Stratifying Thrombotic Risk and Risk Assessment
Thrombotic risk varies based on the patient’s admission reason, the presence of risk factors and the patient’s co-morbidities. All hospitalised patients should be evaluated for VTE risk, bleeding risk, and contraindications to pharmacological VTE prophylaxis.
Baseline assessments include:
renal function (U&Es)
full blood count (FBC)
coagulation profiles if a coagulation disorder is suspected (Coag screen)
Guidelines offer recommendations for prophylaxis based on patient type (medical or surgical) and surgical procedure. Risk assessments should also consider individual patient characteristics and additional VTE risk factors.
Key risk factors include:
previous VTE
thrombophilia
malignancy
postoperative status
trauma
immobility (and more)
Risk stratification for bleeding is essential, as pharmacological agents form the core of VTE prophylaxis. These agents are contraindicated in cases of:
active bleeding
severe thrombocytopenia
presence of coagulation disorders
Non-pharmacological options are recommended for high-bleeding-risk patients:
graduated compression stockings (GCS)
intermittent pneumatic compression (IPC) devices
Clinical scores, such as the IMPROVE bleeding risk score, can assist in assessing bleeding risk and guiding clinical decisions.
Initiating Thromboprophylaxis: Assessing Renal Function and Bleeding Risk
Before starting thromboprophylaxis, several crucial tests should be performed. Renal function assessments are necessary due to drugs like LMWH and fondaparinux being eliminated through the kidneys. Baseline FBC and coagulation profiles should rule out contraindications to pharmacological thromboprophylaxis, such as acute haemoglobin (Hb) or severe thrombocytopoenia. Testing for serum anti-PF4 antibodies is recommended if heparin-induced thrombotic thrombocytopenia (HITT) is suspected.
Pharmacological agents, such as LMWH and fondaparinux, are commonly used for VTE prophylaxis. However, unfractionated heparin (UFH) or low molecular weight (LMWH) should be avoided in patients with a past history of HITT, even without detectable serum anti-PF4 antibodies. Special care is needed when considering neuraxial anaesthesia and analgesia, as spinal haematoma can occur as a rare but potentially severe complication.
Types of Anticoagulation Therapy
When initiating anticoagulation therapy, it's vital to check the patient's bleeding disorder status, full blood count, international normalized ratio (INR), and activated partial thromboplastin time (APTT). The primary methods of anticoagulation include unfractionated intravenous heparin and LMWH in combination with warfarin.
Unfractionated Heparin (UFH):
This is usually indicated when rapid reversal of anticoagulation may be required, but it has become less common.
The aPTT should be checked daily, and the heparin dose adjusted according to a sliding scale.
Low-Molecular-Weight Heparin (LMWH):
Administered subcutaneously, LMWH is widely used in hospitals.
Each hospital may have its preferred brand, and dosing is weight-adjusted as per BNF guidelines.
No routine APTT checks are required, but factor Xa activity may be monitored if necessary.
Reduced doses are often needed in patients with impaired renal clearance.
Starting Warfarin Therapy
Warfarin, a coumarin anti-coagulant, is started alongside heparin treatment. Initially, warfarin has pro-thrombotic effects, which can lead to skin and soft tissue necrosis. It's vital to have heparin cover before initiating warfarin therapy. The standard loading protocol involves administering 10mg of warfarin on the first day, 5mg on the second and third days, with subsequent adjustments based on the INR (but with all medications - always check your local Trust guidelines before prescribing ANYTHING!).
INR Monitoring and Patient Education
Daily INR checks are necessary during the first week, followed by weekly checks for the next three weeks, monthly checks for the following three months, and checks every eight weeks thereafter. The target INR is usually set between 2-3, although this may vary depending on the patient's condition.
Patient education is crucial when starting warfarin therapy (or indeed any new medication). Clearly explain potential side effects and the importance of informing their GP and other healthcare professionals about their anticoagulant use. Patients should also be aware of bleeding risks and symptoms to look out for, and they must inform pharmacists about their warfarin use when purchasing over-the-counter medications.
Side-Effects of Anticoagulation Therapy
Both warfarin and heparin carry the risk of bleeding as a common side effect.
Warfarin may also cause:
alopecia
diarrhoea
purple toes syndrome
hepatic dysfunction with jaundice.
LMWH and unfractionated heparin may cause:
bleeding
heparin-induced thrombotic thrombocytopoenia (HITT)
osteoporosis (with long-term use)
Managing High INR or Bleeding
If the patient’s INR rises too quickly or exceeds 5, warfarin and/or heparin should be stopped. For an INR greater than 10 or in cases of bleeding, administering 4 units of fresh frozen plasma (FFP) can help. Prothrombin complex can be used instead of FFP in some hospitals. Additionally, a small dose of vitamin K (1-2mg) can reverse clotting in a few hours, but caution should be exercised to avoid prolonged anticoagulation disruption.
Conclusion
Anti-coagulation plays a vital role in managing patients with various cardiovascular conditions. As junior doctors and final year medical students, understanding the protocols, monitoring, and potential side effects of anticoagulation is crucial for providing safe and effective patient care. Always consult with senior colleagues and haematologists if faced with challenging cases, and ensure thorough patient education to promote adherence and safety during anticoagulation therapy.
by Dr Ahmed Kazie
