Pulmonary embolism: diagnosis, risk factors and preventive management

Introduction

Pulmonary embolism (PE) is a condition that occurs when a pulmonary artery, or its branches, become blocked by an embolus (Piovella and Iosub, 2016). Most commonly, this embolus is a deep vein thrombosis (DVT) that has originated in the peripheral venous system – typically in the lower limbs (Palareti et al, 2019; Park, 2016). Together, DVT and PE fall under the common umbrella term of venous thromboembolism (VTE). Rarer aetiologies for PE include fat emboli, amniotic fluid emboli, air emboli and foreign bodies, such as from intravenous drug use (Konstantinides et al, 2014). As most PEs are caused by DVT, this article refers to thrombi/blood clots, rather than other possible causes of PE, when describing pathophysiology. Nursing staff have a key role in the identification and risk reduction of PEs to reduce patient morbidity and mortality.

PE is a relatively common condition in the UK (Howard et al, 2018). Thrombosis UK (All-Party Parliamentary Thrombosis Group, 2020) gives an estimated incidence rate for VTE of 1-2 per 1,000 of the UK population. PE is of clinical importance as it can be life threatening; if not identified and treated quickly, it can lead to right-sided heart dysfunction and cardiac arrest.

When left undetected or untreated, PEs are fatal in approximately 30% of cases (Richardson et al, 2020; Rolving et al, 2019; Widimsky, 2013). Roughly 10% of PEs are fatal within the first hour of symptom onset. However, when treated, the morbidity rate falls to 8% (Widimsky, 2013). Unfortunately, identifying PE can be difficult as it has no specific signs or symptoms (Piovella and Iosub, 2016). Only 30-50% of cases of PE are correctly identified (Widimsky, 2013).

Due to the challenges with correctly diagnosing PEs in a timely fashion, the aim for all patients is to provide a quick, accurate diagnosis (Prentice and Wipke-Tevis, 2019). Nurses are well placed to have an important role in the identification, risk reduction and management of PE, in both acute and primary care settings. With nurses increasingly responsible for the triage of patients in primary and secondary care settings, it is critical they are able to:

• Identify at-risk groups for PE;
• Recognise signs and symptoms of PE;
• Identify prevention and management strategies.

Causes and at-risk groups

There are three major elements that increase the likelihood of thrombus formation: blood stasis, hypercoagulability and vessel injury (Park, 2016; Widimsky, 2013). These elements are known collectively as Virchow’s triad (Fig 1). Risk factors that increase the likelihood of VTE can, therefore, be categorised into one of, or a combination of, these three elements.

Blood stasis

Prolonged periods of reduced mobility increase the likelihood that a blood clot will form. As such, surgical procedures and paralysis are significant risk factors for VTE (National Institute for Health and Care Excellence (NICE), 2022a). Additionally, conditions that obstruct or restrict venous blood flow, such as varicose veins or tumours, can also increase the risk of VTE (Konstantinides et al, 2014). Travel-related DVT can occur due to prolonged immobility, particularly during long-distance travel that interferes with venous flow causing venous stasis (NICE, 2018).

Hypercoagulability

Many conditions can increase the risk of clot formation, such as malignancy, pregnancy, thrombophilia and significant trauma (NICE, 2022a). Additionally, certain hormonal medications can increase this risk – most notably, the oral contraceptive pill (OCP) and hormone replacement therapy (HRT) (Palareti et al, 2019).

Vessel injury

Injury to the wall of blood vessels will increase the risk of VTE. Most significantly, this occurs during trauma, childbirth and surgery (NICE, 2022a).

The British Thoracic Society (BTS) guidelines for VTE (Howard et al, 2018) categorise risk factors as major and minor. Major risk factors increase the risk of PE 5-20 fold, while minor risk factors increase the risk two to four times (NICE, 2022a). These factors are shown in Box 1.

More recently, patients who have been infected with SARS-CoV-2/Covid-19 have been identified as having a higher risk of PE (Akiyama et al 2020; Ullah et al, 2020; Van Dam et al, 2020). The cause behind this is yet to be determined, but it is thought to be a combination of factors. Patients with severe Covid-19 often spend significant amounts of time hospitalised with very reduced mobility, which can predispose them to clot formation (Van Dam et al, 2020). Other theories for increased risk of PE in patients with Covid-19 include microvascular damage related to cytokine response, reactive thrombocytosis and a disease-specific hypercoagulable state (Ullah et al, 2020; Van Dam et al, 2020).

Signs and symptoms

The signs and symptoms of PE are non-specific, so it can be difficult to recognise PE from symptoms alone, particularly when just fewer than a quarter of patients with PE will present without signs of DVT (Palareti et al, 2019; Takach Lapner and Kearon, 2013). However, PE should be suspected in a person with:

• Dyspnoea;
• Tachypnoea;
• Pleuritic chest pain
• Features of DVT, including:
  • Leg pain and swelling (usually unilateral);
  • Lower abdominal pain;
  • Redness;
  • Increased temperature and venous distension (NICE, 2022b).

Other possible symptoms include:

• Retrosternal chest pain (due to right ventricular ischaemia);
• Difficulty breathing;
• Cough and/or haemoptysis;
• Dizziness and/or syncope, in severe cases, (due to right ventricular failure).

Other possible signs that may be present include:

• Tachycardia (heart rate >100 beats per minute);
• Tachypnoea (>20 breaths per minute);
• Hypoxia;
• Pyrexia;
• Elevated jugular venous pressure;
• Gallop heart rhythm, a wide split-second heart sound, tricuspid regurgitant murmur;
• Pleural rub;
• Hypotension (systolic blood pressure <90mmHg) and cardiogenic shock (rare signs indicating central PE and/or a severely reduced haemodynamic reserve).

The presence of risk factors – such as pregnancy, previous DVT or PE, active cancer or recent surgery – makes the diagnosis of PE more likely.

Be aware that PE may be completely asymptomatic and be discovered incidentally when assessing for another condition (NICE, 2022b).

Adding these clinical observations and assessments into routine nursing assessments for patients who are at high risk of PEs, or when PE is suspected, can help to identify patients who need further medical management.

Up to 85% of PEs are thought to be caused by DVT (Widimsky, 2013). Approximately 70% of patients with confirmed PE will have identifiable proximal DVTs on ultrasound (Konstantinides et al, 2014). PEs that occur in the absence of DVT are more likely to occur in females, patients aged >75 years, and patients who are taking hormonal contraception (Palareti et al, 2019). Moreover, patients with chronic lung disease – such as chronic obstructive pulmonary disease and interstitial lung disease – are more likely to develop PE in the absence of DVT, further complicating identification (Park, 2016).

The location of the thrombus in the pulmonary vasculature can affect its resulting symptoms. Blood clots that lodge themselves distally in the pulmonary arteries can result in pulmonary infarction, which will present with pleuritic chest pain and haemoptysis (Meyer et al, 2010). Thrombi that lodge themselves more proximally, in the larger arteries, may only present with dyspnoea (Meyer et al, 2010).

Clots that become fixed at the bifurcation of the two main pulmonary arteries (so-called ‘saddle embolisms’) typically present with cardiopulmonary instability and can rapidly become fatal (Wong, 2021). Importantly, the size of the thrombus does not necessarily correlate to the severity of the patient’s clinical condition: large clots can be asymptomatic, while small clots still have the potential to be life threatening (Piovella and Iosub, 2016).

When assessing patients with suspected PE, it is important to remember that they may present with a variety of non-specific symptoms (Prentice and Wipke-Tevis, 2019), making accurate diagnosis a challenge. Conducting a structured clinical examination and interpretation of the findings can help identify patients for whom the clinical suspicion of PE is high.

Clinical examination for patients with PE can be normal but, most commonly, such patients will have tachycardia and tachypnoea (NICE, 2022b). The signs of a DVT may be present, such as an erythematous, swollen, tender calf. Atrial fibrillation may be present when palpating the pulse and, when auscultating the lungs, a pleural rub may be heard. Hypoxia is commonly noted in patients with PE, but it should be borne in mind that patients aged <40 years are often better able to compensate and so may have oxygen saturations of 94-98%.

Patients with more-severe PE may present with signs of low cardiac output (syncope, hypotension, tachycardia) and poor perfusion (confusion, dyspnoea, hypoxia), as well as raised jugular venous pressure (Takach Lapner and Kearon, 2013).

Clinical investigations may also suggest the presence of a PE. The most-frequent electrocardiogram finding in patients with PE is sinus tachycardia, although right bundle branch block can also be seen commonly. Signs of right heart strain, such as T-wave inversion, may also be seen in severe PE cases. Rarely, an S1Q3T3 pattern (an S wave in V1, a Q wave in lead III, and an inverted T wave in lead III) may be present (Morrone and Morrone, 2018).

Chest X-rays will often appear normal in severe PE, but features that may be present include atelectasis, pleural effusion, or elevation of a hemidiaphragm (NICE, 2022b). Chest X-rays are largely used for ruling out other causes of dyspnoea, such as pneumothorax or pneumonia.

Most commonly, a D-dimer blood test will be used as a simple, fast and inexpensive screening method to exclude PE in patients with possible PE (Gao et al, 2018). A negative D-dimer test result (in patients who have a low or moderate pre-test probability of PE) can be used to safely rule out a diagnosis of PE (Crawford et al, 2016). Those with a negative D-dimer test result will not need further testing.

In patients with a high pre-test probability of PE, a D-dimer test should not be used; rather, these patients should be considered for a computed tomography pulmonary angiogram (CTPA) (Crawford et al, 2016). A D-dimer test can give a negative result in the presence of a PE, so a negative test would not safely rule out PE in these patients. Conversely, a positive D-dimer test result can be caused by many factors such as inflammation, malignancy, pregnancy, trauma and older age. As such, low- or moderate-risk patients with a positive D-dimer test result require further testing before a diagnosis of PE can be confirmed. This is usually a CTPA or ventilation perfusion scan.

“Large clots can be asymptomatic, while small clots still have the potential to be life-threatening”

Prevention: summary of key points

The prevention of VTE can be achieved by acting to avoid the components of Virchow’s triad. To avoid haemostasis, wherever possible, patients admitted to hospital should be encouraged to mobilise early and often, particularly after surgery. Until a patient is able to mobilise, compression stockings should be worn.

Haemostasis can also be reduced by treating varicose veins, controlling arrhythmias and carrying out VTE risk assessments upon hospital admission in all patients. VTE assessments are used to identify the risk of VTE in all hospitalised patients, ideally before the first consultant review (NICE, 2019); this places nursing teams as key in identifying risk.

Planning for appropriate and timely discharge from the acute setting for patients who are at increased risk of VTE also calls for nursing teams to provide appropriate advice and support for patients and their families (NICE, 2019).

Support for patients in primary care or community settings would require nurses to not only identify high-risk patients, but also offer advice to minimise the risk of VTE – for example, by offering advice to patients who are considering long-distance travel (NICE, 2018). Having specific advice for travellers dependent on their VTE risk is recommended. Generic advice for all long-distance travellers (NICE, 2018) includes:

• Regular mobility;
• Calf-muscle exercises;
• Maintaining fluid intake;
• Avoidance of alcohol or sleeping tablets (NICE, 2018).

Specialist advice for high-risk patients should be considered; compression stockings and low molecular weight heparin may both be indicated, but local pathways should be followed (NICE, 2018).

Hypercoagulability can be reduced by encouraging patients to stop smoking (Senst et al, 2022). Clinicians should be cautious about prescribing the OCP or HRT to patients at risk of VTE. Patients in a hypercoagulable state, such as pregnant women or patients with cancer, should be counselled on, and monitored for, VTE.

Assessment of all surgical and trauma patients is required to reduce the risk of VTE, and nurses must use a published tool (NICE, 2019). Pregnant women should all have a VTE assessment on admission to hospital; as should women who have given birth, had a miscarriage or termination of pregnancy in the last six weeks (NICE, 2019).

Reassessment of VTE and the possible need for thromboprophylaxis is required within six hours of giving birth, having a miscarriage or termination of pregnancy (NICE, 2019), or if there is any change in clinical condition.

Management

Treatment for PEs aims to prevent thrombus progression and recurrent embolisation, and reduce the risk of mortality (Kruger et al, 2019). For a suspected PE, immediate hospital admission should be arranged when:

• There are signs of haemodynamic instability (including pallor, tachycardia, hypotension, shock and collapse);
• The individual is pregnant;
• The person has given birth in the previous six weeks.

For other patients with suspected PE, the Wells scoring system (Table 1) can be used to estimate the probability of PE being present (Wells et al, 2003).

For a Wells score of >4, hospital admission should be arranged for CTPA. If a CTPA cannot be organised, interim therapeutic anticoagulation therapy should be provided and hospital admission arranged (NICE, 2020).

For a Wells score of ≤4 (when PE is unlikely), a D-dimer test should be arranged within four hours. If this is not possible, interim therapeutic anticoagulation therapy should be arranged (NICE, 2020). If the D-dimer test result is positive, immediate hospital admission for a CTPA should be arranged; if CTPA is not possible, interim anticoagulation therapy should be arranged (NICE, 2020). If the D-dimer test result is negative, any commenced anticoagulation therapy should be discontinued and an alternative diagnosis sought (NICE, 2020).

Ambulatory pathways for the management of confirmed PEs are an option to manage suitable patients in the community, rather than as inpatients (Howard et al, 2018). Patients can be screened via the Simplified Pulmonary Embolism Severity Index (sPESI) (Table 2); those who score zero should be considered for ambulatory care.

Suitable patients who have a confirmed PE, or who have suspected PE and are awaiting CTPA results, can have the first dose of anticoagulant administered in the assessment area, with further appropriate treatment arranged with the ambulatory care team. They should be given the appropriate information and discharged home, with follow-up in ambulatory care clinics and further investigations provided, as necessary.

Patients should be excluded from ambulatory pathways if there is any clinical evidence of:

• Shock/hypovolemia;
• Pregnancy (Howard et al, 2018);
• Right ventricle dilation with elevated cardiac enzymes (NT-proBNP/troponin levels);
• Social concerns (such as inability to return home or concerns over compliance) (Howard et al, 2018).

PE can be a frequent complication in patients with cancer (Ay and Posch, 2020). Due to high risk of haemorrhage, thrombolysis is not a recommended standard treatment for patients who are haemodynamically unstable (Ay and Posch, 2020). The current standard of care for cancer-associated PE is anticoagulation therapy for six months with low-molecular-weight heparin (LMWH) or a novel oral anticoagulant (NOAC) (Ay and Posch, 2020).

Patients with gastrointestinal malignancies (such as oesophagogastric and colorectal cancer) should be administered NOACs cautiously, due to an increased bleeding risk when compared with LMWHs (Ay and Posch, 2020).

Patients who inject intravenous drugs, particularly those who inject into central veins, are at risk of DVT (Jain et al, 2021). This cohort of patients can present a challenge in managing PEs due, in part, to chaotic lifestyles (Howard et al, 2018). Oral anticoagulation is rarely prescribed due to the risk of non-compliance with medication regimes and monitoring (Jain et al, 2021). Patients with suspected or confirmed PE will usually be admitted to hospital for close monitoring and investigation (Howard et al, 2018), and subsequently managed for 3-6 months with LMWHs. This cohort of patients is usually treated with co-administration of antibiotics because PE in this group is often associated with sepsis (Klester, et al, 2017).

Most patients who present with PE are treated successfully and do not develop complications. Complications can, however, potentially be serious and include:

• Collapse and cardiac arrest;
• Death;
• Heart failure;
• Recurrent PEs;
• Bleeding;
• Pulmonary hypertension for small repeated PEs.

Nursing considerations in the management of PE include:

• Maintaining levels of activity to prevent venous insufficiency by encouraging mobilisation and active leg exercises;
• Monitoring thrombolytic and anticoagulant therapy with the international normalised ratio blood test or the partial thromboplastin time blood test;
• Managing pain;
• Turning the patient often and repositioning them to improve their ventilation-perfusion ratio;
• Assessing for signs of hypoxemia, managing oxygen therapy and monitoring pulse-oximetry values;
• Relieving anxiety by encouraging the patient to talk about any fears or concerns they may have;
• Providing appropriate support with discharge planning – this includes advice to reduce the risk of VTE, such as keeping well hydrated and increasing mobility levels;
• Informing patients, family and carers of the signs and symptoms of a DVT and PE, and where to seek appropriate help if one is suspected (Belleza, 2021; NICE, 2019).

Nurses have a huge role to play in the management of patients with PE and VTE. Specialist nursing VTE roles can provide an important educational and advisory capacity for health practitioners, as well as the appropriate initiation and monitoring of treatment, including improving the care pathway for patients (Filipino UK Nurses, 2021). Specialist nurses can help reduce unnecessary hospital admissions and have a pivotal role to play in research and service improvement. However, all nurses should work towards PE prevention and management, as outlined above.

Conclusion

PE is a relatively common condition in the UK and can be life threatening if not identified and treated quickly. The signs and symptoms of PE are non-specific, so recognising it from symptoms alone can be difficult, particularly when a sizeable proportion of patients with PE will present without signs of DVT. However, for a suspected PE, immediate hospital admission should be arranged. The Wells score can be used to estimate the probability of PE and the sPESI screening tool used to help determine an appropriate clinical pathway.

Nurses play a pivotal role in the management of patients with PE through identification, treatment, monitoring, education and support. Timely diagnosis and treatment can lead to significant reduction in mortality and morbidity rate, so nurses need to be aware of risk factors to identify high-risk patients. Nurses also have a key role to play in preventing PE and reducing risk by providing appropriate assessments and ongoing risk-reduction strategies as part of their routine clinical practice.