What are the risk factors and preventive measures for pulmonary embolism (PE)?

Risk Factors for Pulmonary Embolism

Pulmonary embolism results from the interaction between patient-related (usually permanent) and setting-related (usually temporary) risk factors, with major trauma, surgery, lower-limb fractures, cancer, and immobilization representing the strongest provoking factors. 1

Strong Provoking Factors (Temporary)

The following represent the highest-risk temporary factors that dramatically increase PE risk:

• Major trauma and surgery are among the strongest provoking factors for venous thromboembolism 1
• Lower-limb fractures and joint replacements (hip or knee) carry particularly high risk 1, 2
• Spinal cord injury is a strong provoking factor 1
• Recent immobilization or major surgery within the preceding weeks 1
• Myocardial infarction within the previous 3 months significantly increases risk 2
• Hospitalization for heart failure or atrial fibrillation/flutter within the previous 3 months 2

Major Patient-Related Risk Factors (Often Permanent)

These factors represent ongoing or recurrent risk:

• Cancer is a well-recognized predisposing factor, with pancreatic cancer, hematological malignancies, lung cancer, gastric cancer, and brain cancer carrying the highest risk 1
• Previous venous thromboembolism (DVT or PE) is a strong risk factor for recurrence 1, 2
• Clinical deep vein thrombosis at presentation 1
• Pregnancy and the postpartum period, particularly with operative delivery 1

Cardiorespiratory and Medical Conditions

• Congestive cardiac failure and chronic symptomatic cardiorespiratory disease (including irreversible airways disease) 1
• Congenital heart disease 1
• Stroke and other neurological diseases causing lower limb immobility (brain tumor, acute spinal injury) 1

Hormonal and Medication-Related Factors

The risk varies substantially by formulation and generation:

• Combined oral contraceptives (containing both estrogen and progestogen) increase VTE risk approximately 2- to 6-fold over baseline 1, 2
• Third-generation combined oral contraceptives (containing desogestrel or gestodene) carry higher VTE risk than second-generation formulations (levonorgestrel or norgestrel) 1
• Hormone replacement therapy in postmenopausal women, with risk varying widely by formulation 1
• Hormone-releasing intrauterine devices and progesterone-only pills (at contraceptive doses) are NOT associated with significant VTE risk increase 1

Other Significant Risk Factors

• Infection is a common trigger for VTE 1
• Blood transfusion and erythropoiesis-stimulating agents are associated with increased VTE risk 1
• Age over 40 years (risk increases exponentially with age) 1, 2
• Obesity has been confirmed as an independent risk factor 1
• Central venous catheters 1
• Prolonged air travel due to lower limb immobility 1

Risk Stratification for Clinical Practice

When assessing PE probability, the British Thoracic Society recommends scoring patients based on:

Score +1 if other diagnoses are unlikely (on clinical grounds and after basic investigations) 1

Score +1 if a major risk factor is present:

• Recent immobilization or major surgery
• Recent lower limb trauma and/or surgery
• Clinical deep vein thrombosis
• Previous proven DVT or PE
• Pregnancy or postpartum
• Major medical illness 1

Important Clinical Caveats

• PE is rare if age <40 with no risk factors 1
• Oestrogens are only a minor risk factor when considered in isolation 1
• Over 70% of cases of fatal or non-fatal proven PE have proximal thrombus, even though this is usually clinically undetectable 1
• The incidence of venous thromboembolism is particularly high when there are multiple risk factors present simultaneously 1
• Inherited thrombophilia should be considered in those without another apparent explanation, though it is unusual for these to present as unheralded PE 1

Preventive Measures

Pharmacological and physical measures to reduce postoperative DVT risk in high-risk patients have achieved substantial reduction in fatal PE incidence, though wide variations in practice exist and protocols may be overlooked in emergency surgery patients 1

• Consider initial assessment of provoking risk factors for the index PE at an early stage (immobility, surgery, cancer, intercurrent illness) since this determines duration of anticoagulation 1
• Screening for malignancy should have mechanisms in place to review results within a prompt time frame when performed 1