Care of the surgical patient—part 2: oral anticoagulants

Anticoagulation therapy

Anticoagulant therapy and its role in the treatment of cardiovascular disorders (people with atrial fibrillation and mechanical prosthetic heart valves) is well recognised (National Institute for Health and Care Excellence (NICE), 2020); however, there is now an increased awareness and acceptance of its use to treat and prevent stroke and thromboembolism, all of which have implications for patients who are undergoing surgery (Pavord and Webster, 2015; Douketis and Lip, 2019). If prescribed anticoagulants are continued during surgery or invasive procedures, the risk of bleeding increases and additional potential harm may occur from the use of regional anaesthetics, including epidurals; however, if they are stopped, further thromboembolisms may develop (Keeling et al, 2011). Therefore, for patients receiving anticoagulation therapy, perioperative management must be holistically tailored, dependent on the patient's current medication, international normalised ratio (INR), thromboembolism risk and the type of surgery/anaesthetic that the patient is scheduled to receive (Association of Anaesthetists of Great Britain and Ireland (AAGBI), 2016; Dubois et al, 2017). With recent developments in pharmacology, there is now a range of direct oral anticoagulants (DOAC), such as apixaban, dabigatran, edoxaban and rivaroxaban, which have a fast onset of action; however, this article will focus on vitamin K antagonists and heparin, as these are the most commonly used (McIlmoyle and Tran, 2018).

Vitamin K antagonists, as the name would suggest, inhibit several coagulation processes in which vitamin K is a co-factor (McIlmoyle and Tran, 2018). Namely, this is the conversion of glutamine acid to y-carboxyglutamic acid, which is needed for the synthesis of prothrombin (coagulation factor ii), proconvertin (coagulation factor vii), plasma thromboplastin component (coagulation factor ix) and Stuart-Prower factor (coagulation factor x), and natural anticoagulants protein S and C (Pavord and Webster, 2015). The most commonly used vitamin K antagonist is warfarin (AAGBI, 2016). Warfarin is orally bioavailable and rapidly absorbed in the gastrointestinal tract; however, it has a varied half-life and causes many pharmacological interactions. These can decrease the effectiveness of the warfarin, increasing the risk of clot formation or the risk of bleeding and haemorrhage. Therefore, warfarin requires careful and close monitoring, especially when administered alongside drugs that are known to interact with it, such as paracetamol, ibuprofen, aspirin-based medications and antacids or laxatives (Pavord and Webster, 2015).

Heparins are sulphated glycosaminoglycans that are isolated from porcine tissue (Martin and Hine, 2014). They are used for their ability to inhibit blood coagulation by binding to antithrombin and enhancing its ability to inhibit thrombin production and fibrin clot formation, which are involved in the coagulation cascade process (see Figure 1) (Pavord and Webster, 2015). The two main types of heparin are unfractured heparin (UFH) and low molecular weight heparin (LMWH); however, LMWH is usually preferred over UFH because LMWH has increased bioavailability and the potential for reduced side effects (McIlmoyle and Tran, 2018; Douketis and Lip, 2019) (see Table 1).

International normalised ratio

INR is a laboratory test used to check the anticoagulant effect of warfarin by using the outcome of the prothrombin time (PT) test, a measurement that monitors the time it takes blood to coagulate (Anderson et al, 2019). The target INR for those prescribed anticoagulants is ideally 2.5 (therapeutic range between 2 and 3), or 3.5 for individuals with recurrent venous thromboembolisms (VTEs) (Keeling et al, 2011; Pavord and Webster, 2015; AAGBI, 2016; NICE, 2020). If the patient's INR is 1.5 or above at the time of surgery, the balance of the risk of haemorrhage versus the urgency of undertaking the operation must be considered by the surgical team. Ideally, INR should also be measured the day before an operation in patients taking warfarin so that vitamin K can be administered if the INR is 1.5 or above, as this reverses warfarin's effect of inhibiting the synthesis of vitamin K-dependent clotting factors, reducing the risk of bleeding and the possible need to cancel the surgery (Keeling et al, 2011; NICE, 2020). If surgery is required urgently, prothrombin complex concentrate can be used to reverse warfarin anticoagulation (Pavord and Webster, 2015), and to reverse the effects of heparin, protamine sulfate can be used to ensure the action of thrombin and fibrin in the coagulation cascade (AAGBI, 2016).

Thromboembolism risk

VTE is the overarching term used to describe deep vein thrombosis (DVT) and pulmonary embolism (PE) and is associated with the formation of a blood clot, known as a thrombus, in a vein. Thrombi have the potential to become dislodged, creating an embolism in another part of the body (Duff et al, 2013; Rayt and Nasim, 2015). A thrombus usually develops in one of the larger and deeper veins of the body (most commonly the deep veins of the pelvis, thigh and lower leg). They are more prevalent in individuals whose blood is hypercoagulable and can also be caused by venous injury and venous stasis. As the body usually relies on movement and contraction of the lower limb muscles to assist with venous return, surgical patients, especially those undergoing a general anaesthetic and who are thus immobile, are therefore at higher risk of developing a thrombus. VTE is a major cause of death in hospitalised patients, with approximately 6500 annual deaths attributed to VTE in the UK, many of which could be avoidable (NICE, 2019). Consequently, VTE prevention has been recognised as a clinical priority for the NHS and completion of a VTE risk assessment is required for all patients admitted to hospital, just after admission or before the first consultant review (NICE, 2019). This also has significance for surgical patients, as deaths due to postoperative strokes are substantially higher than fatalities because of bleeding (Keeling et al, 2011; NICE, 2020). These risk assessments can be used to help determine and document if a patient is at increased risk of developing a thrombus as well as their risk of bleeding, both of which are taken into account when making decisions on whether anticoagulants are continued, stopped or if bridging therapy is required (Douketis, 2019). An example of a general VTE risk assessment is given in Table 2).

Type of surgery

Another factor used when making a decision about treatment is also related to the surgery type, the surgical site and the individual patient's anatomy (Keeling et al, 2016). For example, if patients are undergoing procedures with a low risk of bleeding including minor dermatological surgery, a biopsy of a site that can be compressed to stop bleeding or joint aspiration/injection, anticoagulants may be continued (Keeling et al, 2011; Dubois et al, 2017). In contrast, for procedures with a high risk of bleeding, such as cardiovascular surgery, thoracic surgery, spinal surgery, liver and kidney biopsy, major abdominal surgery, cranial surgery and orthopaedic surgery, anticoagulants may need to be stopped (Lai et al, 2014). Keeling et al (2016) suggested that although some surgeries can be considered at a lower or higher risk of bleeding, each case should be examined individually, and decisions to reduce, stop or replace anticoagulants should be made collaboratively between the operating team and patient. If it is necessary to stop warfarin before a procedure, individuals should be instructed to cease medication 5 days before the surgery, INR should be measured on the day before surgery, to allow administration of vitamin K if it is greater than or equal to 1.5 and re-checked on the morning of surgery if vitamin K has been administered (AAGBI, 2016).

Bridging therapy

In anticoagulant therapy, bridging therapy refers to a pharmacological bridge that is created during a period when warfarin therapy is interrupted and when the INR is not within a therapeutic range. Medications that may be used for bridging therapy include UFH and LMWH eg tinzaparin (AAGBI, 2016). Bridging therapy may be required both preoperatively and postoperatively to balance the risk between a thromboembolism forming and major haemorrhage during the surgical intervention and patients will need to remain on this bridging therapy until they can resume their usual anticoagulant. If the patient has undergone surgery with a high risk of postoperative bleeding, it may be necessary to wait at least 48 hours before commencing bridging therapy (Keeling et al, 2016).

However, bridging therapy should not be used routinely, as warfarin should never be interrupted for procedures of low bleeding risk or when patients are assessed as being at low risk of thromboembolism (Douketis and Lip, 2019). For patients who are at intermediate risk, the decision for perioperative use will depend on the type of surgery and whether there is an increased risk of bleeding during or after the surgery and this will be patient-specific (McIlmoyle and Tran, 2018). For high-risk patients, bridging therapy should be considered and warfarin should be stopped 5 days before the surgery (see Table 3) (AAGBI, 2016).

Neuraxial and peripheral nerve blocks

The AAGBI et al (2013) have recommended that regional anaesthesia should be used where possible for high-risk patients due to the postoperative benefits of early mobility and the continuation of anticoagulant therapy. However, careful consideration must be undertaken with regard to the use, insertion and removal of epidurals or spinal anaesthesia/analgesia for patients who are receiving anticoagulant therapy, as clinically significant bleeding can cause neurological dysfunction (Horlocker, 2011; AAGBI et al, 2013). During insertion, coagulation status (INR) must be within the therapeutic range and postoperative removal of indwelling catheters should never be undertaken if the patient has been recommenced on therapeutic anticoagulation therapy. Additionally, if the insertion is traumatic, the restarting of anticoagulant medication postoperatively may need to be delayed due to the risk of bleeding, haematoma formation and subsequent nerve damage (Horlocker, 2011).

Patients with epidural and spinal blockades must be monitored closely for any signs of neurological dysfunction in the postoperative period, as prompt interventions may be required (AAGBI et al, 2013). This observation should be undertaken by qualified, trained staff who are aware of the significance and the action required if any abnormal values are recorded. Epidural blockades are known to cause hypotension (low blood pressure); however, it is important to be mindful that, postoperatively, hypotension can occur for various reasons, such as myocardial insufficiency, sepsis or dehydration, so these should be considered and excluded (AAGBI et al, 2013). Postoperatively, if haemostasis has been achieved, warfarin can usually be recommenced at the maintenance dose on the first evening or the following day (Keeling et al, 2016).

Conclusion

The increase in the number of individuals living with complex needs and comorbidities means that the NHS is treating more and more surgical patients (Holt, 2012; Dhatariya et al, 2016; Keeling et al, 2016). Patients who are undergoing continuous anticoagulant therapy are more at risk of several conditions, such as severe headaches, stomach pain and vision changes, but bleeding is a frequent issue that these individuals face. It is the responsibility of every health professional to ensure that all patients are as safe as possible, so when these patients require surgical intervention, it is important that altered management strategies and associated risks are a part of healthcare education to ensure continued safety for these patients. Approximately eight million surgical interventions are carried out every year by the NHS. Therefore the continued awareness of conditions and diseases, such as cardiovascular disorders that impact the care of the surgical patient (such as people with atrial fibrillation and mechanical prosthetic heart valves) is an important part of becoming a well-rounded and inclusive nurse or perioperative practitioner.

KEY POINTS

CPD reflective questions