When Is It Appropriate to Work Up a Pulmonary Embolism in the Trauma or Post-Operative Patient?

Pulmonary embolism (PE) can be a fatal complication for any patient.  One of the most difficult tasks for clinicians is determining an appropriate threshold of clinical signs and symptoms that deem examinations like a CTA of the chest to be more beneficial than harmful to a patient with a suspected PE. 

One set of criteria used to determine clinical characteristics of a patient who is suspected of PE where the benefit of receiving a diagnostic radiologic exam would outweigh its risks of receiving that examination is the Pulmonary Embolism Rule-out Criteria (PERC).  The difficulty in applying this criteria to the post-operative or post-traumatic injury patients is that, according to the criteria, all of these patients will receive more benefit than harm from further CT workup.  Unfortunately PERC has a very low specificity (23%) in adequately diagnosing PE⁽¹⁾ which leads to many unnecessary CT scans.

Other clinical scales used for the detection of PE like the Wells criteria and Geneva score all are able to assign probable risk of PE from low (4-10%) or intermediate (13-40%) to high (67-80)⁽²⁾.  Again, the difficulty with these scales is they were developed for an otherwise low-risk patient population suspected of a PE.  Recent post-operative or trauma patients who are tachycardic or where PE is deemed likely via clinical judgment are immediately placed into the intermediate risk and likely receive a CT scan even if they only have a 13-40% chance of having a PE.

The intent of this review is to gather research over the last five years that can better guide clinicians on specific clinical criteria of the post-operative patient to utilize diagnostic imaging with increased specificity for detecting PE in order to reduce unnecessary imaging.  This review was conducted via PubMed with the keywords “post-operative pulmonary embolism”, “post-traumatic pulmonary embolism”, “traumatic embolism”, and “embolism threshold”. 

Research found in this literature search stratified risk according to several different categories.  Risk of PE was based on type of surgery^(3-5), weeks post-operation⁽⁴⁾, and thrombotic prophylaxis⁽⁵⁾.  The surgeries most associated with post-operative PE in these studies were major abdominal surgery related to colorectal cancer⁽⁵⁾ and knee or hip replacement in middle aged women⁽⁴⁾.  This study of middle aged women also determined that the first twelve post-operative weeks provide the greatest risk of PE.  While these criteria provide a pre-operative stratification of who will be at increased risk and a general timeline for how long patients have increased risk of PE, none of these studies provided specific clinical criteria that could be found in the post-operative assessment of a patient that would confidently tell a physician to favor PE in his differential diagnosis.  In fact, only one of these studies even provided a generalized criteria of “breathing difficulty, pleuritic chest pain, and pleural rubs” that made the physician concerned enough to work-up a PE in their post-operative patients. 

However, one study out of Germany did attempt to create a post-operative finding that had a very high specificity for PE.  Prell, et al, found that in post-craniotomy patients an elevated D-dimer of 2 mg/L had both a high sensitivity (95.3%) and specificity (74.1%) for venous thromboembolism (VTE) ⁽⁶⁾.  The study determined that while D-dimer levels rise in post-operative patients, both with and without PE, but the rise in D-diner levels of those patients with a PE was far greater.  In fact D-dimer levels of >4mg/L were observed in all patients (n=9) who had a venous thrombotic event.  Additionally, the most pronounced difference in D-dimer levels between VTE+ and VTE- post-operative patients was found on day 3 when VTE+ group had a mean D-dimer of 5.49mg/L while the D-dimer of the VTE- group was only 1.59m/L.   This study has provided both a measurable value in patients that is specific for PE and a timeline when one can expect the PE.  The total N of this study was small (n=101), but considering the significant difference between the two groups this type of trial could prove very beneficial if expanded to a larger sample size.

The data for a highly sensitive and specific threshold for using diagnostic imaging in suspected PE patients is very limited at this time.  Most information gathered at this time concerns the type of surgery involved.  However, with new ideas concerning the use of post-operative D-dimer as a clinical marker for PE it may soon be possible for clinicians to more confidently use radiographic imaging to diagnose a PE leading to less unnecessary uses of diagnostic imagery.

 References

1.  Diagnostic accuracy of pulmonary embolism rule-out criteria: a systematic review and meta-analysis. Singh B, Parsaik AK, Agarwal D, Surana A, Mascarenhas SS, Chandra S.  Ann Emerg Med. 2012 Jun;59(6):517-20.e1-4.

2.  Dynamed: Clinical Prediction of Pulmonary Embolism. Accessed October 28, 2013. http://dynamed.ebscohost.com

3.  Risk factors of venous thromboembolism in Indian patients with pelvic-acetabular trauma. Sen RK, Kumar A, Tripathy S, Aggarwal S, Khandelwal N. J Orthop Surg (Hong Kong). 2011 Apr;19(1):18-24.

4.  Duration and magnitude of the postoperative risk of venous thromboembolism in middle aged women: prospective cohort study. Sweetland S et al. BMJ. (2009)

5.  A study of pulmonary embolism after abdominal surgery in patients undergoing prophylaxis. Kerkez MD et al. World J Gastroenterol. (2009)

6.  D-dimer plasma level: a reliable marker for venous thromboembolism after elective craniotomy. Prell J, Rachinger J, Smaczny R, Taute BM, Rampp S, Illert J, Koman G, Marquart C, Rachinger A, Simmermacher S, Alfieri A, Scheller C, Strauss C. J Neurosurg. 2013 Aug 6.

From Joe Puetz MS4