Saad Tarabichi, Eric Smith.
Response/Recommendation: Advances in imaging have resulted in an increased ability to visualize emboli in the lungs, some of which may be clinically non-significant and may even not be a true pulmonary embolism (PE). The “gold standard” for diagnosis of PE is still the computer tomography pulmonary angiography (CTPA).
Strength of Recommendation: Strong.
Rationale: The risk of deep venous thrombosis (DVT) and PE in patients undergoing surgery is well established. In the context of orthopaedic surgery, patients undergoing elective total hip/knee replacement are considered at highest risk for developing venous thromboembolism (VTE). Manifestation of VTE in these patients includes DVT and subsequent PE that can be fatal. Prior to rapid post-operative patient mobilization, some historical estimates have put the incidence of DVT without prophylaxis to be between 40% and 84% after total knee arthroplasty (TKA), and around 39% to 74% for patients undergoing total hip arthroplasty (THA)1. Over the years, comprehensive guidelines on venous thromboembolism prevention have been established. These include measures such as prevention with effective preoperative and postoperative anticoagulation, to more conservative measures like early and aggressive postoperative mobilization, pneumatic compression stockings, and tools to identify high-risk patients2. Despite this, the National Institute of Health (NIH) projects that the number of patients needing joint arthroplasty and consequently the number of thromboembolic complications is on the rise3.
In the past, the gold standard for the diagnosis of suspected PE was the two-dimensional ventilation-perfusion (V/Q) scan. Sostman et al.4, estimated the sensitivity and specificity of a V/Q scan, when used to diagnose PE, to be around 77.4% and 97.7%, respectively. However, the Prospective Investigation of Pulmonary Embolism Diagnosis (PIOPED) I clinical trials showed that V/Q imaging reported an uncertain likelihood for PE in 65% of confirmed PE cases, indicating that a V/Q scan could not make a reliable diagnosis5. Parvizi et al.6, showed that over their study period of five years, the incidence of PE rose from 0.21% when using V/Q scans to 0.98% with spiral CT and peaked at 1.72% with the introduction of multidetector CT. Newer techniques like the multidetector-row CTPA proved to be more sensitive for detecting PE. CTPA has also been shown to have exceptionally high specificity for diagnosing PE. The PIOPED II trial estimated that CTPA had a sensitivity of 83% and specificity of 96%, respectively7. Despite only being introduced in 1998, by 2006 several institutions documented a 7-to-13-fold increase in the utilization of CTPA8–11. It is now considered the gold standard for the diagnosis of PE. Parvizi et al. 6, also suggested that more advanced imaging techniques, like CTPA, have led to an increase in incidence of non-clinically significant PE. In other words, they have caused a rise in detection of abnormalities that are not harmful and cause no increase in morbidity or mortality. Previous investigators have examined trends in incidence of PE before and after the introduction of CTPA. An 81% increase in incidence of PE was noted with no significant increase in mortality. Furthermore, there was a 71% increase in complications secondary to anticoagulation12. Overdiagnosis of PE resulting in unnecessary harm to patients who are anticoagulated for non-clinically significant PE is an important clinical issue. Ranji et al., reported that 25.4% of their patients had false-positive CTPA findings and were subsequently treated with anticoagulants13. Another benefit is that CTPA can identify the location of the emboli within pulmonary arteries. Some studies have shown that the size and location (central versus segmental or subsegmental) of clots correlate with clinical severity. Auer et al.8, stated that patients with central PE were more likely to require intensive care unit (ICU) admission and had higher 30-day mortality rates. Additionally, the authors of a different study proposed that subsegmental emboli are non-clinically significant even when they are left untreated14. However, Valle et al., found that there is no association between PE location and clinical severity (calculated by employing the PE Severity Index)15.
Outcomes in patients with VTE have significantly improved over the last two decades. Despite a recent rise in incidence of DVT and PE following orthopaedic procedures, recent studies have shown that morbidity and mortality secondary to these disorders is at an all-time low6. This is due to the established international guidelines on preoperative optimization and risk stratification of patients undergoing surgery16. Additionally, our ability to effectively diagnose patients with PE has substantially increased since the worldwide incorporation of the CT scan. We now know that once commonly used imaging modalities, such as V/Q scans, are not as reliable as previously believed. With constant developments in medical imaging, we must ensure judicious use of advanced imaging. Currently, CTPA appears to be the most accurate and effective imaging modality for the diagnosis of suspected PE. Given the risks posed to patients receiving anticoagulation with clinically non-significant emboli, we recommend the prudent use of CTPA only in patients with high clinical suspicion or high pretest probability of pulmonary embolus.
References:
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