The Journal of TRAUMA௡ , Infection, and Critical Care

Incidence of Asymptomatic Pulmonary in Moderately to Severely Injured Trauma Patients David J. Schultz, MD, Karen J. Brasel, MD, MPH, Lacey Washington, MD, Lawrence R. Goodman, MD, Robert R. Quickel, MD, Randolph J. Lipchik, MD, Todd Clever, BS, and John Weigelt, MD

Background: Chest computed tomo- sessed using an anatomic scoring system. patients receiving pharmacologic prophy- graphic (CT) scanning is used frequently Patients not receiving anticoagulation laxis had a PE. to evaluate symptomatic patients for pul- were followed. Conclusion: Asymptomatic PE occur monary embolus (PE). The incidence of Results: Twenty-two of 90 patients in 24% of moderately to severely injured PE diagnosed by helical CT scanning in had a PE. Four had major clot burden, patients. Age, head, chest, and lower ex- asymptomatic patients is unknown. including one patient with a saddle embo- tremity injury are associated with an in- Methods: Asymptomatic trauma pa- lus. Risk factors for asymptomatic PE in- creased risk. Standard thromboembolic tients with an > 9 clude age (odds ratio [OR], 1.04), head prophylaxis is not reliably protective. were studied with contrast-enhanced heli- injury (OR, 6.78), (OR, 4.51), Key Words: Computed tomographic cal CT images of the chest, pelvis, and lower extremity injury (OR, 5.03), and scanning, Pulmonary embolus, Head in- lower extremities. Clot burden was as- transfusion (OR, 3.42). Thirty percent of jury, Chest injury, Transfusion. J Trauma. 2004;56:727–733.

hromboembolic complications are common in the uate respiratory symptoms in these patients. Many of these trauma population. Depending on the severity and type scans show atelectasis or pulmonary consolidation, and the Tof injury as well as the method of prophylaxis, the patient’s symptoms resolve with appropriate treatment. How- prevalence of proximal deep venous thrombosis (DVT) and ever, in these symptomatic patients, the scans occasionally pulmonary embolus (PE) can approach 20%.1 Prophylaxis show small pulmonary emboli. This raises a new question: against thromboembolic disease in these patients is aimed are we finding thromboembolic disease that is clinically in- against both DVT and PE, with the assumption that it is significant, or are we finding thromboembolic disease before equally effective against both. Screening the lower extremi- it becomes clinically significant? ties with venous Doppler examinations either once or twice Most prospective studies of PE in injured or postopera- weekly is based on the assumption that the majority of pul- tive patients have been conducted on symptomatic monary emboli develop from venous thrombosis in the pelvis patients.3–6 In patients with deep venous thrombosis or those or lower extremities.2 undergoing major abdominal or orthopedic procedures, the Respiratory complications are also common in injured prevalence of unsuspected or asymptomatic pulmonary em- patients. The pain from chest injury, particularly rib fractures, boli is approximately 25%.7–16 Injured patients can also be at frequently causes splinting and inadequate expansion, leading high risk for DVT and pulmonary emboli, but the prevalence to atelectasis and pneumonia. Enforced recumbency caused of asymptomatic pulmonary emboli remains unknown. The by associated exacerbates this problem. Chest com- purpose of this study was to determine the incidence of PE puted tomography is used with increasing frequency to eval- diagnosed by helical computed tomographic (CT) angiogra- phy in asymptomatic trauma patients and the consequences of withholding anticoagulation in patients with minor clot Received for publication September 24, 2003. burden. Accepted for publication December 31, 2003. Copyright © 2004 by Lippincott Williams & Wilkins, Inc. From the Departments of (D.J.S., K.J.B., T.C., J.W.) and PATIENTS AND METHODS Radiology (L.W., L.R.G.) and Division of Pulmonary Medicine, Department of Medicine (R.J.L.), Medical College of Wisconsin, Milwaukee, Wisconsin, This prospective cohort study was approved by the and Department of Surgery, Hennepin County Medical Center (R.R.Q.), institutional review boards at the Medical College of Wis- Minneapolis, Minnesota. consin and Froedtert Memorial Lutheran Hospital. Con- Presented at the 62nd Annual Meeting of the American Association for secutive trauma patients with an Injury Severity Score the Surgery of Trauma, September 11–13, 2003, Minneapolis, Minnesota; (ISS) Ն 9 without symptoms suggestive of a pulmonary Second Place, Clinical Investigation, Resident Trauma Papers Competition, 2003. embolus or deep venous thrombosis were studied on Address for reprints: Karen J. Brasel, MD, MPH, Department of Sur- postinjury days 3 to 7. This time interval was chosen gery, Medical College of Wisconsin, 9200 West Wisconsin, Milwaukee, WI because it is the interval during which initial screening for 53226; email: [email protected]. asymptomatic deep venous thrombosis in high-risk trauma DOI: 10.1097/01.TA.0000119687.23542.EC patients is recommended.3 In addition to documented

Volume 56 • Number 4 727 The Journal of TRAUMA௡ Injury, Infection, and Critical Care thromboembolic disease or symptoms suggestive of a deep venous thrombosis or pulmonary emboli, patients were excluded for the following reasons: mechanical ventila- tion, renal failure, iodine allergy, pregnancy, and age younger than 18 years. Patients on were excluded because of the difficulty in determining whether these patients were truly asymptomatic. After obtaining informed consent, 120 mL of nonionic contrast was injected and the patient was scanned from apex to diaphragm on a 16-slice multidetector helical CT scanner using 1.25-mm axial images and a 0.7-second rota- tion time (GE Lightspeed 16, Milwaukee, WI). After 3.5 minutes, 5-mm axial images every 2 cm from the iliac crest to the knees were obtained to evaluate the iliac, common femoral, and popliteal veins. Scans were initially interpreted by the on-call radiologist to screen for large pulmonary em- boli or deep venous thrombosis potentially requiring urgent treatment. The primary service was notified immediately about all scans with significant positive findings. All scans Fig. 1. Segmental pulmonary embolus seen in the white circle as the were then read by one of two experienced faculty chest segmental pulmonary artery branches into subsegmental arteries. radiologists. Emboli were scored using a modification of the Miller scoring system.17 This anatomic scoring system ranges RESULTS from 0.25 to 20 and is based on the pulmonary artery and its Ninety-four consecutive patients were enrolled. Eighty- segments. Each main pulmonary artery with clot receives a six eligible patients refused consent during the same period. score of 10, each segmental artery a score of 1, and each Three patients were excluded because their ISS was less than involved subsegmental artery a score of 0.25. Patients were 9 on final review, and one patient was excluded because of classified according to clot burden as follows: 0.25 to 2.0, poor scan quality (a result of morbid obesity). Of the 90 minimal burden; and 2.25 to 4.0, moderate burden. Clot evaluable patients, 22 patients (24%) were diagnosed with Burden Greater than 4.25: Major Burden; Glot burden greater PE. Eighteen patients had minor clot burden and four had than 4.25, major burden. major clot burden. Three quarters of the patients with minor Patients with suspected DVT underwent duplex exami- clot burden had subsegmental emboli (single or multiple) nation to confirm the presence of DVT. Treatment recom- only (Fig. 1). One of the patients with major clot burden had mendations based on clot burden were given, but ultimate a saddle embolus (Fig. 2). The four patients with major clot treatment and/or plans for further follow-up in patients with either deep venous thrombosis or pulmonary emboli was determined by the primary service. Recommendations in- cluded no treatment for minimal clot burden without coexis- tent DVT, and treatment of any patient with moderate or major clot burden or minor clot burden with a coexistent DVT. DVT was scored as absent, acute, or chronic. Age, gender, injury mechanism, organ injury, Abbrevi- ated Injury Scale score, ISS, need for blood transfusion, use of sequential compression devices, and use of prophylactic anticoagulation were analyzed for association with pulmo- nary embolism. Outcomes of hospital and intensive care unit length of stay were compared. All patients were phoned 3 months after discharge and questioned about complications, respiratory symptoms, lower extremity symptoms, and bleeding problems using a symp- tom checklist. Mailed questionnaires and chart review were used to ascertain follow-up when phone contact was not possible. Statistical analysis was performed using Student’s t Fig. 2. Saddle pulmonary embolus seen in the left and right main test, Fisher’s exact test, and multivariate regression. pulmonary arteries circled in black.

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embolus received low-molecular-weight heparin as prophy- Table 1 Demographic Data laxis, as did another patient with major clot burden; two other PE Present PE Absent patients with major clot burden and the patient with the No. 22 68 coexistent DVT had only mechanical prophylaxis. Age (yr) 40.7 31.7 None of the 17 patients with minor clot burden were ISS 20.1 15.5 anticoagulated, and none had signs or symptoms of pulmo- Male (%) 88 85 Mechanism (% blunt) 75 44 nary embolus during hospitalization. Ten of 17 patients with Transfused PRBCs (% 56 28 minor clot burden were followed at 3 months and had no receiving transfusion) symptoms or complications attributable to thromboembolic PRBCs, packed red blood cells. disease. An additional three patients were asymptomatic at 1-month clinic follow-up. There were no deaths. burden were therapeutically anticoagulated. An additional patient with minor clot burden and a coexistent DVT was also DISCUSSION therapeutically anticoagulated. This was the only patient with The prevalence of asymptomatic pulmonary emboli is a DVT. The remaining patients with minor clot burden were dependent on the population studied and the diagnostic test not anticoagulated. used. In patients with symptomatic DVT, the prevalence of Patients with pulmonary emboli were older (40.7 vs. 31.7 asymptomatic pulmonary emboli diagnosed by ventilation/ 7–10 years) and were more severely injured (ISS 20.1 vs. 15.5) perfusion scan and angiography is 12% to 50%. Using (Table 1). They were more likely to have had a blunt injury angiography as the sole diagnostic test results in a slightly 11 mechanism (75% vs. 44%) and more likely to have received higher prevalence of 56%. Disappearance of the perfusion transfusions (56% vs. 28%). Patients with asymptomatic em- defect after treatment suggested that the emboli were real, 7 boli had a longer hospital stay than those without emboli despite lack of symptoms. (10.1 vs. 5.3 days, p Ͻ 0.01). In the multivariate model, age, The incidence of asymptomatic emboli in our trauma blood transfusion, and significant head, chest, or lower ex- population is similar to the 20% incidence at autopsy in 17 tremity injury were associated with asymptomatic emboli trauma patients that died as a result of a nonembolic cause. (Table 2). Gender, injury mechanism, and use of prophylaxis It is also similar to the incidence reported in several other were not associated with embolism in the multivariate model. high-risk populations without DVT. Evaluated using ventila- Patients that refused consent did not differ from enrolled tion/perfusion scan, the perioperative prevalence of asymp- patients with respect to age, gender, ISS, or mechanism of tomatic pulmonary emboli in patients undergoing general 12,13 injury. surgery is 12% to 16%. A similar incidence is found in Forty patients received pharmacologic prophylaxis (Ta- postoperative orthopedic patients using ventilation/perfusion ble 3). Pharmacologic prophylaxis, including low-molecular- scans and in patients undergoing cardiac 14–16,18 weight heparin and unfractionated heparin administered three catheterization. In adult patients undergoing a Fontan times daily, was not protective against asymptomatic pulmo- operation, 17% have asymptomatic emboli diagnosed by sin- 19 nary embolism. Patients with pulmonary emboli received gle-detector helical CT angiography. low-molecular-weight heparin as prophylaxis more often than Asymptomatic emboli are also reported in groups of patients that did not have pulmonary emboli, although this patients without risk factors. In an age group approximating was not statistically significant. The patient with the saddle the general trauma population, Wallace et al. found pulmo- nary emboli in 3% of nonsmokers aged 18 to 29 years using ventilation/perfusion scans.20 Without restriction on age or Table 2 Variables Associated With Asymptomatic smoking status, the incidence increases to 25%.21 Using sin- Pulmonary Emboli gle-detector helical CT scanning, unsuspected PE were de- Odds Ratio (95% CI) p Value tected in 1.5% of patients having routine contrast-enhanced Age (yr) 1.04 (1.01–1.08) 0.04 scans. The incidence was 10-fold higher for inpatients com- 22 Blood transfusion 3.42 (1.06–11.02) 0.04 pared with outpatients (5% vs. 0.6%). Head AIS score Ͼ2 6.78 (1.42–32.45) 0.02 A clear question regarding these asymptomatic emboli Chest AIS score Ͼ2 4.51 (1.09–18.75) 0.04 revolves around the accuracy of CT angiography. The sensi- Ͼ Lower extremity AIS score 2 5.03 (1.14–22.12) 0.03 tivity and specificity of helical chest CT angiography for AIS, ; CI, confidence interval. diagnosis of pulmonary embolism has a wide range of re- ported values. Sensitivity ranges from 64% to 93%, with a 23–26 Table 3 DVT Prophylaxis specificity of 89% to 100%. Accuracy increases with increasing experience and manipulation of slice thickness, DVT Prophylaxis PE Present (%) PE Absent (%) collimation, and pitch.24 As with angiography, accuracy for None or mechanical only 10 (20) 40 (80) CT angiography is highest for central emboli. Although con- Pharmacologic 12 (30) 28 (70) sidered the “gold standard” diagnostic test, interobserver

Volume 56 • Number 4 729 The Journal of TRAUMA௡ Injury, Infection, and Critical Care agreement regarding the presence of subsegmental emboli on emboli. Anticoagulation itself is not without risk, and pulmonary angiography is only 13% to 66%.5,27 Although not the 1% to 2% incidence of major bleeding complica- performed in our series, interobserver agreement is much tions may be a greater risk than is posed by these higher for CT angiography than for conventional emboli.35 angiography.28 Comparative series of CT and standard an- 3. Are we using the right screening tests? Currently, giography specific to subsegmental emboli report false-neg- many protocols include periodic screening with lower ative results for subsegmental emboli on CT angiography but extremity venous Doppler examinations. Given that not a significant false-positive rate, suggesting that our esti- the fatal thromboembolic disease is pulmonary embo- mate is, if anything, low.23,29 If the subsegmental emboli lism rather than deep venous thrombosis, should high- found in this study are excluded, our incidence of approxi- risk patients be screened with helical chest CT angiog- mately 4% is similar to the 5% incidence of asymptomatic raphy instead? emboli in the inpatient population reported by Gosselin et al. 4. When do these emboli occur? On review of admission Only main, lobar, or segmental emboli were evaluated in this chest CT scans, subsegmental emboli were present in 1998 report, as the single-detector scan technology was not two of our patients at the time of their initial trauma sophisticated enough to reliably detect subsegmental evaluation. Others have found segmental as well as emboli.22 lobar emboli on chest CT scans obtained as a part of The advances in CT scanning technology have led to the initial trauma evaluation, in the first several hours increased accuracy for not only central but also segmental after injury.29,36 and subsegmental emboli. These advances include the use of 5. Where do these emboli originate? Coexistent deep multidetector rather than single-detector scanners, thinner venous thrombosis was found in only a single patient, collimation, and increased gantry speed.30 Sensitivity and suggesting in situ thrombosis, origin in the upper ex- specificity compared with arteriography reach 90% and 94%, tremities, or evidence of a systemic disease with early respectively, even at the subsegmental level.31 Preliminary manifestation in the pulmonary circulation. Prophylac- data suggest excellent accuracy down to fifth-order subseg- tic inferior vena cava filter placement would not be mental arteries when multidetector technology is used.32 expected to prevent emboli in any of these scenarios. These reports used 2- and 4-slice multidetector technology; 6. How effective is our prophylaxis in high-risk injured the current study used a 16-slice multidetector scanner, ex- patients? Thirty percent of the patients receiving phar- plaining our ability to detect subsegmental emboli. macologic prophylaxis of some type had a pulmonary Risk factors associated with asymptomatic pulmonary embolus. Prophylaxis protocols may need to be reas- emboli are similar to those for previously identified posttrau- sessed, given this prevalence of asymptomatic pulmo- matic thromboembolic complications.33 However, eight pa- nary emboli. tients with asymptomatic pulmonary emboli would have been classified as low risk by this risk assessment profile score. CONCLUSION The high prevalence of asymptomatic pulmonary emboli Moderate to severely injured trauma patients have a in this patient population on routine helical chest CT angiog- significant incidence of asymptomatic pulmonary emboli. raphy raises many issues. These questions include the Further study and understanding of thromboembolism in in- following: jured patients is needed to improve our evaluation, prophy- 1. What is the clinical significance of these asymptom- laxis, and treatment of this complication. atic pulmonary emboli? The majority of our patients were not anticoagulated because they had no coexist- ing DVT and only minor clot burden. These patients ACKNOWLEDGMENTS had no known untoward sequelae. Should a grading The authors would like to thank Scott Schwantes for help with data system, similar to the Miller system, be used to help collection and Clare Guse, MS, for statistical analysis. guide treatment of asymptomatic pulmonary emboli? The natural history of these asymptomatic emboli REFERENCES needs further study to answer these questions. 1. Geerts WH, Code KI, Jay RM, Chen E, Szalai JP. A prospective 2. Should these asymptomatic pulmonary emboli be study of venous thromboembolism after . N Engl J Med. 1994;331:1601–1606. treated, and if so, how? Although consensus opinion 2. Hull RD, Hirsh J, Carter CJ, et al. Pulmonary angiography, suggests treatment for all discovered pulmonary em- ventilation lung scanning, and venography for clinically suspected boli regardless of symptoms,25,34 others have followed pulmonary embolism with abnormal perfusion lung scan. Ann Intern a more individualized treatment approach.29 Many of Med. 1983;98:891–899. these trauma patients have contraindications to antico- 3. Knudson MM, Collins JA, Goodman SB, McCrory DW. Thromboembolism following multiple trauma. J Trauma. 1992;32:2– agulation and are at too young an age to subject them 11. to potential long-term complications of a vena cava 4. Kim K, Müller NL, Mayo JR. Clinically suspected pulmonary filter, the alternative prophylaxis against pulmonary embolism: utility of spiral CT. Radiology. 1999;210:693–697.

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5. The PIOPED Investigators. Value of the ventilation/perfusion scan in 25. Rathbun SW, Raskob GE, Whitsett TL. Sensitivity and specificity of acute pulmonary embolism: results of the prospective investigation helical computed tomography in the diagnosis of pulmonary of pulmonary embolism diagnosis (PIOPED). JAMA. 1990; embolism: a systematic review. Ann Intern Med. 2000;132:227–232. 263:2753–2759. 26. ACCP Consensus Committee on Pulmonary Embolism. Opinions 6. Michiels JJ. Rational diagnosis of pulmonary embolism (RADIA PE) regarding the diagnosis and management of venous thromboembolic in symptomatic outpatients with suspected PE: an improved strategy disease. Chest. 1998;113:499–504. to exclude or diagnose venous thromboembolism by the sequential 27. Quinn MF, Lundell CJ, Klotz TA, Finck EJ, Pentecost M, McGehee use of a clinical model, rapid ELISA D-dimer test, perfusion lung WG. Reliability of selective pulmonary arteriography in the scan, ultrasonography, spiral CT, and pulmonary angiography. Semin diagnosis of pulmonary embolism. Am J Radiol. 1987;149:469–471. 28. Schoepf UJ, Helmberger T, Holzknecht N, et al. Segmental and Thromb Hemost. 1998;24:413–418. subsegmental pulmonary arteries: evaluation with electron-beam 7. Huisman MV, Buller HR, ten Cate JW, et al. Unexpected high versus spiral CT. Radiology. 2000;214:433–439. prevalence of silent pulmonary embolism in patients with deep 29. van Rossum AB, Pattynama PM, Ton ER, et al. Pulmonary venous thrombosis. Chest. 1989;95:498–502. embolism: validation of spiral CT angiography in 149 patients. 8. Moser KM, Fedullo PF, LitteJohn JK, Crawford R. Frequent Radiology. 1996;201:467–470. asymptomatic pulmonary embolism in patients with deep venous 30. Remy-Jardin M, Tillie-Leblond I, Szapiro D, et al. CT angiography thrombosis. JAMA. 1994;271:223–225. of pulmonary embolism in patients with underlying respiratory 9. Moser KM, LeMoine JR. Is embolic risk conditioned by location of disease: impact of multislice CT on image quality and negative deep venous thrombosis? Ann Intern Med. 1981;94:439–443. predictive value. Eur Radiol. 2002;12:1971–1978. 10. Monreal M, Ruiz J, Olazabal A, Arias A, Roca J. Deep venous 31. Ghaye B, Szapiro D, Mastora I, et al. Peripheral pulmonary arteries: thrombosis and the risk of pulmonary embolism: a systematic study. how far in the lung does multidetector-row spiral CT allow analysis. Chest. 1992;102:677–681. Radiology. 2001;219:629–636. 11. Kistner RL, Ball JJ, Nordyke RA, Freeman GC. Incidence of 32. Qanadli SD, El Hajjam M, Mesurolle B, et al. Pulmonary embolism pulmonary embolism in the course of thrombophlebitis of the lower detection: prospective evaluation of dual-section helical CT versus extremities. Am J Surg. 1972;124:169–176. selective pulmonary arteriography in 157 patients. Radiology. 2000; 12. Hirsch JF, Demilly P. Screening of asymptomatic pulmonary 217:447–455. by systematic scintigraphy in apparently uncomplicated 33. Gearhart MM, Luchette FA, Proctor MC, et al. The risk assessment phlebitis. Ann Med Intern. 1991;142:168–170. profile score identifies trauma patients at risk for deep vein 13. Browse NL, Clemenson G, Bateman NT, Gaunt JI, Croft DN. Effect thrombosis. Surgery. 2000;128:631–640. of intravenous dextran 70 and pneumatic leg compression on 34. Romano WM, Cascade PN, Korobkin MT, Quint LE, Francis IR. prevalence of postoperative pulmonary embolism. BMJ. 1976; Implications of unsuspected pulmonary embolism detected by 2:1281–1284. computed tomography. Can Assoc Radiol J. 1995;46:363–367. 35. Landefeld SC, Beyth RJ. Anticoagulant-related bleeding: clinical 14. Williams JW, Eikman EA, Greenberg S. Asymptomatic pulmonary epidemiology, prediction, and prevention. Am J Med. 1993;95:315– embolism: a common event in high-risk patients. Ann Surg. 1989; 328. 195:323–327. 36. Rogers FB, Osler TM, Shackford SR. Immediate pulmonary 15. Foley M, Maslack MM, Rothman RH, et al. Pulmonary embolism embolism after trauma: case report. J Trauma. 2000;48:146–148. after hip or knee replacement: postoperative changes on pulmonary scintigrams in asymptomatic patients. Radiology. 1989;172:481–485. 16. Dorfman GS, Cronan JJ, Tupper TB. Occult pulmonary embolism: a common occurrence in deep venous thrombosis. AJR Am J DISCUSSION Roentgenol. 1987;148:263–266. Dr. David H. Wisner (Sacramento, California): My 17. Havig Ö. Deep vein thrombosis and pulmonary embolism: an thanks to the Association for the opportunity to discuss this autopsy study with multiple regression analysis of possible risk nicely written and also, I might say, well-presented article. factors. Acta Chir Scand. 1977;478(suppl):1–108. The authors do raise some provocative questions about how 18. Primm RK, Segall PH, Alison HW, et al. Incidence of new pulmonary perfusion defects after routine cardiac catheterization. we are diagnosing both pulmonary embolism and, tangen- Am J Cardiol. 1979;43:529–532. tially, deep venous thrombosis using CT scanning, and sug- 19. Varma C, Warr MR, Hendler AL, Paul NS, Webb GD, Therrien J. gest that the incidence of pulmonary embolism may be quite Prevalence of “silent” pulmonary emboli in adults after the Fontan a bit higher than traditional testing methodologies have so far operation. J Am Coll Cardiol. 2003;41:2252–2258. led us to believe. 20. Wallace JM, Moser KM, Hartman T, Ashburn WL. Patterns of I have a couple of questions. The authors in the article pulmonary perfusion in normal subjects. Am Rev Respir Dis. 1981; cite several studies in which the false-positive rate for CT 124:480–483. 21. Tetalman MR, Hoffer PB, Heck LL, Kunzmann A, Gottschalk A. scan diagnosis of PE was quite low. Perfusion scans in normal volunteers. Radiology. 1973;106:593–594. When I looked at these studies, they’re actually (espe- 22. Gosselin MV, Rubin GD, Leung AN, Huang J, Rizk NW. cially given the rapidly expanding state of the technology in Unsuspected pulmonary embolism: prospective detection on routine the CT scanning area) relatively dated studies at this point. helical CT scans. Radiology. 1998;208:209–215. That raises the question about whether it’s possible that, with 23. Mullins MD, Becker DM, Hagspiel KD, Philbrick JT. The role of ever-improving CT scanning technology, what these studies spiral volumetric computed tomography in the diagnosis of pulmonary embolism. Arch Intern Med. 2000;160:293–298. are showing actually aren’t emboli at all but false-positives. 24. Remy-Jardin M, Remy J, Deschildre F, et al. Diagnosis of The authors bring up in the article the possibility that pulmonary embolism with spiral CT: comparison with pulmonary these pulmonary emboli aren’t clinically important. I would angiography and scintigraphy. Radiology. 1996;200:699–706. ask the somewhat metaphysical question, are they even there

Volume 56 • Number 4 731 The Journal of TRAUMA௡ Injury, Infection, and Critical Care or are they just a by-product of ever-improving CT scanning One comment and one question. The comment is that I am technology? surprised that the patient with what appeared to be a saddle I especially wondered this when I looked at some of the embolus was truly asymptomatic. It looked pretty impressive examples on the screen. As with many radiographic studies, on the CT scan. My question is as follows: these small emboli when I look at them, the things that were circled were, in in the peripheral arteries, are they the sequelae of a larger clot some instances, very convincing and in other instances not so that has broken up, that was present earlier and you’re just convincing. catching it at a later time frame, or are these small clots that Another question I have that’s an issue at our institution are embolizing? is how technician-dependent are the quality of the scans you Dr. Susan M. Briggs (Boston, Massachusetts): Excel- obtained? Has that been an issue for you, also? lent article. A quick question for the authors. Given the A somewhat related question but having this time to do current enthusiasm for our medical colleagues to use fragmin with radiologists: did you test interobserver variability of the for DVT rather than heparin, was there any correlation CT readings in any way? In other words, did the radiologists whether patients were on subcutaneous heparin or subcuta- always agree when you had two or three of them look at a neous fragmen as used in many trauma patients? given CT scan? Did they all agree that there were, in fact, Dr. Michael L. Hawkins (Augusta, Georgia): Two defects? Did you test that in any way? questions. First—it’s probably in your article but you didn’t Finally, as a bottom-line question. I’m curious as to state it—what was the incidence of DVT that you found in whether or not this study has changed your practice. Do you these same patients? Second, and you may have trouble with use CT scanning as a screening modality, either for pulmo- the institutional review board, it would be useful to know the nary embolism or for deep venous thrombosis? denominator, that is, study patients who aren’t as sick or I really enjoyed the article and look forward to further perhaps patients who have no significant illness at all. investigations in this area. Thank you. Dr. Carol R. Schermer (Albuquerque, New Mexico): Dr. Tetsuo Yukika (Tokyo, Japan): I enjoyed your ar- I’d also like to know what your indication was for obtaining ticle very much. Could you identify the reason why you the CT scan and, specifically, what did you tell the institu- excluded a patient with a ventilator? Thank you. tional review board or the patient your indication was for Dr. George C. Velmahos (Los Angeles, California): I obtaining a contrasted CT in an asymptomatic patient? would like to congratulate the authors for a very elegant study Dr. David J. Schultz (closing): I’d like to thank Dr. and for bringing to our attention two important issues. The Wisner for his interesting comments and questions along with one is that if you look for PE, you will find it. The incidence the other members who have asked questions. The real ques- is much higher than we think it is. Second, prophylactic tion with this study is, are pulmonary emboli really there or measures do not work. are we finding something that’s not really there? In our We and others have shown that heparin and leg com- pression devices simply don’t work in critically injured pa- institution, we really rely on the helical CT scan to detect tients. I would like to ask the authors whether they have given pulmonary embolus. We use a 16-detector scanner, which is any consideration or thought as to why that happens. Why better than the 4-detector scanner with which it has been does heparin, which probably works in other groups of pa- proven that the fourth to fifth order of pulmonary arteries are tients, not work in the trauma population? able to be evaluated. Dr. John T. Owings (Sacramento, California): Yes, I We have a very close working relationship with our would like to compliment the authors as well for bringing radiologists and GE medical systems and have the latest something to our clinical attention that has been in the pa- software, and our radiologists use the CT scan as their gold thology literature for some time, which is, that patients who standard for pulmonary embolus. There have been very few die have a much higher incidence of pulmonary embolism pulmonary angiograms obtained in our institution in the past than what we recognize clinically. My question for the au- 5 years. thors is based on my observation that they’ve demonstrated As for the scans being technician-dependent, we have a their own superfluousness in the study by showing that the standard protocol with a standard injection rate, thin collima- patients in this study did not demonstrate significant tion, and we always generate 1.25-mm images, so it’s not sequelae. technician-dependent. It’s always the same protocol. What do the authors do clinically now when they’re We had two chest radiologists reading these, and they looking for pulmonary embolism? Have they validated the had excellent agreement. CT scan in their institution, not for patients who are asymp- Yes, we do use CT scanning now exclusively to look at tomatic, but specifically for patients in whom they suspect pulmonary emboli. There are very few pulmonary angio- pulmonary embolism and who are on a ventilator and who are grams, like I said, and very few ventilation/perfusion scans, at sick? Thank you. least in the trauma population. As for isolated DVT, we still Dr. Daniel R. Margulies (Los Angeles, California): I’d continue to use ultrasound and do not routinely use the CT like to congratulate the authors on an excellent presentation. scan to evaluate for DVT.

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We decided to exclude the ventilator patients because Regarding the correlation between low-molecular- it was difficult to determine whether they were truly weight heparin and unfractionated heparin, our sample size asymptomatic from a PE standpoint. They can’t complain was too small, really, to look at this, and this wasn’t the of shortness of breath and so forth, so that’swhywe primary outcome of our study. It would require more patients excluded them. to look at that. Why the heparin is not prophylactic in these patients is a As for the incidence of DVT, we surprisingly only had one good question. It has been the topic of several studies. One patient in our entire study group that had coexisting DVT. We possibility is the decreased level of antithrombin III seen in only looked at the pelvic veins and the thigh veins with the CT trauma patients. There also may be a genetic vulnerability to scan. We may have missed DVT down in the tibial veins. this disease. As for the indication for the CT scan, we did explain to Like I said, our radiologists have validated the CT scan with them that this was a study protocol and that the benefit of their relationship with GE, and they use the CT scan now to rule obtaining the CT scan is that we may find something we out PE in our institution, and it really hasn’t changed our prac- didn’t suspect there, and it was for our study. Again, I would tice. We’ve been doing it now for several years. like to thank the Association for the opportunity to present.

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