On which post-operative day is pulmonary embolism (PE) most likely to occur?

From the Guidelines

Pulmonary embolism is most likely to occur between post-operative days 3 to 7, with the highest risk typically around day 5. To understand this risk, it's essential to consider the natural history of venous thromboembolism (VTE), which includes deep vein thrombosis (DVT) and pulmonary embolism (PE). The risk of VTE is highest during the first two post-operative weeks but remains elevated for two to three months 1.

Key Points to Consider:

• The incidence of VTE is reduced with increasing duration of thromboprophylaxis after major orthopaedic surgery and, to a lesser extent, cancer surgery 1.
• The majority of patients with symptomatic DVT have proximal clots, complicated by PE in 40–50% of cases, often without clinical manifestations 1.
• The rate of recurrence is highest during the first two weeks and declines thereafter, with active cancer and failure to rapidly achieve therapeutic levels of anticoagulation appearing to independently predict an increased risk of recurrence 1.

Prevention Strategies:

1. Start early mobilization within 24 hours after surgery, if possible, to reduce the risk of VTE.
2. Use mechanical prophylaxis (compression stockings or intermittent pneumatic compression devices) immediately after surgery to prevent DVT.
3. Administer pharmacological prophylaxis, such as low molecular weight heparin (e.g., enoxaparin 40 mg subcutaneously once daily) or unfractionated heparin (5000 units subcutaneously every 8-12 hours), starting 6-12 hours post-operatively for most patients, as suggested by recent guidelines 1. Continue these preventive measures until the patient is fully mobile or discharged, typically for 7-14 days post-surgery. For high-risk patients, extend prophylaxis for up to 35 days. The timeline for the highest risk of PE correlates with the physiological changes post-surgery, including the activation of clotting mechanisms for healing, prolonged immobility, and the stress response to surgery, which can lead to excessive clot formation and, subsequently, PE as patients begin to mobilize around day 3-7 1.

From the Research

Post-operative Pulmonary Embolism Timing

• The exact post-operative day when pulmonary embolism (PE) is most likely to occur is not explicitly stated in the provided studies.
• However, according to the study 2, the risk of postoperative pulmonary embolism is highest during the first 5 weeks after surgery, with the highest risk during the immediate postoperative period (1 to 6 weeks).
• Another study 3 presents a case of a patient with pulmonary embolism diagnosed on the third day after cancer-related laparoscopic prostatectomy, suggesting that PE can occur early in the post-operative period.
• Study 4 found that pulmonary embolism developed in most patients within 2 weeks of a coronary bypass operation, but does not specify the exact day.
• Overall, while the exact day is not specified, the risk of pulmonary embolism appears to be highest in the early post-operative period, particularly within the first 1-6 weeks after surgery 2.