Ultrasound Examination of Deep Vein Thrombosis during Pregnancy - Coursework Example

Ultrasound Examination of Deep Vein Thrombosis during Pregnancy Introduction Pregnancy is a physiological condition where venous stasis may be associated with a state of hypercoagilability. Despite this as opposed to anticipation, the incidence of symptomatic and clinically detectable deep venous thrombosis (DVT) in pregnancy has been reported to be low. In case of DVT in pregnancy, the problem is further complicated by its diagnosis and management, in that due to the risks of fetal exposure the imaging studies have limited roles. This may lead to delayed diagnosis, and the management of an established DVT is widely debated due to fetal risks associated with maternal administration of anticoagulants. Deep venous thrombosis was classically diagnosed by venography, which has its own problems in a pregnant patient. Recently with development of suitable technology, noninvasive methods such as plethysmography and specifically Doppler ultrasonography are being increasingly used to diagnose clinically silent deep venous thrombosis in pregnant individuals. The clinical criteria of deep venous thrombosis are rarely apparent in many cases, and some actual cases of DVT are termed as superficial phlebitis (Chan et al., 2002). Thus a diagnostic modality that can establish the diagnosis would be very necessary due to initiate management and prevent complications which may be detrimental to the fetus and life-threatening to the mother. Mortality rates of thromboembolism in pregnancy have been reported to be 15% in untreated patients and less than 1% in treated patients. This substantiates the grounds for establishing an early diagnosis and treatment based on that. It is quite evident that the reasons the patients remain untreated are ill-defined clinical manifestations, need for a very index of suspicion, lack of guideline regarding routine screening examinations for DVT in pregnant women, unavailability of a dependable and reliable noninvasive test, consequent failure to establish the diagnosis, and resultant failure to initiate treatment, all of which culminate into death of 15% pregnant women affected with DVT, much of which can be prevented with the use of a noninvasive and easy to use diagnostic imaging procedure (Ray and Chan, 1999). Early diagnosis and early intervention remain the clues to successful outcome specially in pregnant women since missing the diagnosis has potentially fatal implications. Over the top of that misdiagnoses have implications of potentially unnecessary risks of anticoagulation therapy such as teratogenic effects of drugs in the first trimester and the risk of fetal intracranial bleeding in the third trimester. The clinical criteria for diagnosis of DVT are unreliable, and objective testing is the mainstay of definitive diagnosis. Ultrasonographic examination of the deep veins is rapidly becoming acceptable as the investigation of choice for screening, diagnosis, and decision for management (Scarvelis and Wells, 2006). Ultrasonographic Diagnosis Scarvelis and Wells (2006) indicated that the imaging study of choice for DVT in pregnancy is compression ultrasonography. With venous thrombosis in a any segment of a vein, there is lack of usual compressibility of the involved venous segment, and this lack of compressibility is the diagnostic criterion for this study. Recent advent of Doppler ultrasonogram with colour flow almost accurately images the vessels involved and confirms the lack of compressibility in an area of thrombosed vein. While DVT by definition is not restricted to any particular area, the commonest sites of occurrence are in the lower extremities and usually in the proximal venous segment. Guidelines Therefore, in many guidelines, ultrasonographic testing of for DVT is kept limited to the proximal segments of the vein (Scarvelis and Wells 2006). For a lower extremity, this would mean the area from the common femoral vein to an area distally in the region of the popliteal vein where the femoral vein joins it. As reported by Kearon et al. (1998), the sensitivity of ultrasonographic testing in this vein for DVT is in the range of 97% (Kearon et al. 1998). For diagnostic management of DVT, as has been indicated by Cogo et al. (1998), there is a rationale for omitting distal calf veins for initial and routine screening; however, it has been recommended that if the initial test result in negative in the proximal femoral artery, a second ultrasonographic examination should be indicated of the distal calf regions after one week, since it may take time for the thrombus to extend into the proximal veins as a part of serial testing regimens. In their metaanalysis, Wells et al. (1995) discussed the issue of routine serial ultrasound testing to explore its need. In the case of possible extension of the thrombus from the distal to the proximal segments, although it appears to be an act an omission, in reality in the patients with symptomatic DVT, only 20% of these thrombi have been reported to have originated in the calf muscles, and out of these all, only 20 to 30% will extend eventually to the proximal venous segments (Wells et al. 1995). Thus Perone and his colleagues (2000) argue that given the number of possible patients being very less, the sensitivity is not affected sizably by this omission, and thus routine serial testing becomes inefficient, inconvenient, and disadvantageous from the cost-benefit point of view (Perone et al., 2000). Ultrasonography: Limitations It is to be remembered that ultrasonography has problem with false positive results. Acute DVT is pathologically occlusive, and by not being echogenic, there is a chance that ultrasound examination based on principles of echogenicity may fail to detect discontinuous thrombi, unless serial testing is included in the protocol. For these purposes, the consensus is to consider an increase in the clot diameter by 4 mm to be suggestive of recurrence and extension. For nonocclusive thrombi, a Doppler ultrasound examination may produce consistently reliable results (Chan et al., 2002). Chan and Ginsberg (2002) highlighted the problems of DVT in pregnant women and the issue of lack of imaging algorithm which may be safe and accurate. There are many reasons for this, but the most important is lack of dependable evidence from clinical studies involving pregnant women. It has already been mentioned that there is a resistance to imaging studies by both the pregnant mothers and clinicians due to possibility of exposure to ionizing radiations, which makes contrast venography, pulmonary angiography, and ventilation-perfusion scans defunct in such cases. Moreover pregnancy is a condition where physiologic and anatomic changes in the lower extremity veins due to pregnancy per se even in an unaffected mother make the diagnostic accuracy of objective studies dubious. Moreover, symptomatic DVT may be mimicked by nonthrombotic lower extremity swelling, calf pain, or shortness of breath (Chan and Ginsberg 2002). Serial Compression Ultrasound Although serial compression ultrasound has been recommended in pregnancy to detect DVT as an option for quick screening without chances of harm to the mother or the fetus, it is important to note that many patients may be asymptomatic, and there is possibility of high degree of false positive tests. As discussed in Cordts and Gawley (1996), there are certain inherent changes in the coagulation system in pregnant mothers. Fibrinogen and factor VIII are increased, coagulation inhibitor protein S is decreased, and these remain fairly uniform throughout pregnancy and even continue into puerperium. As a result of hormonal influences on vascular tone and compressive effects of enlarging uterus on the pelvic veins, there is considerable venous stasis in pregnancy, and a combined effect of these factors may lead to increased predisposition of DVT in pregnancy (Cordts and Gawley 1996). Given the sensitivity of serial compression ultrasound, it is now accepted to be a safe and effective diagnostic strategy for symptomatic proximal DVT. Although contrast venography remains the gold standard for such events, compression ultrasonography is an acceptable test given its 97% sensitivity and 94% specificity for the symptomatic proximal DVT, although it is less accurate in diagnosing DVT isolated in the cuff veins, for which serial testing in a 7-day time has been recommended. Given the issues of pelvic pressures in pregnant women, compression ultrasonography may be an inadequate test for detection of occult and isolated iliac vein thrombosis. This clinical situation deserves special mention due to the fact that there is a high risk of development of pulmonary embolism in such cases (Chan and Ginsberg 2002). Therefore, further testing is indicated even though the ultrasonographic examination is normal. Therefore in suggestive cases, a pulsed Doppler can be very useful in diagnosing isolated iliac vein thrombosis as initial screening, while only MRI has been observed to having the requisite high sensitivity and specificity required for a diagnostic accuracy (Polak and O’Leary, 1988). A Possible Protocol As far as ultrasonographic objective diagnostic testing of DVT in pregnant women is concerned, thus a protocol may be designed based on evidence from different studies, some involving pregnant women and some extrapolated from the studies on nonpregnant individuals, given the paucity of studies. On presentation with asymmetrical leg swelling as an index symptom, an initial compression ultrasonography can be performed (Perrier et al., 1999). A positive study would indicate DVT. If this test proves to be negative and symptoms of isolated iliac vein thrombosis such as swelling of the entire leg and back pain are absent, a serial testing protocol may be instituted over a period of next 1 to 2 weeks (Frede and Ruthberg, 1988). Although superficial thrombophlebitis has been of no significant clinical importance, given its natural course of tendency to develop an extension to deep veins, a serial compression ultrasonographic testing over a period of next 7 days to rule out extension into deep veins seems to be prudent. In cases of suspected isolated calf vein thrombosis, in order to rule out proximal propagation, a serial ultrasonographic testing over the next 2 weeks would be a legitimately rational course of action (Chan and Ginsberg 2002). Doppler Ultrasonography Lensing et al. (1989) indicated the utility of Doppler ultrasonography in detection of DVT in pregnancy. In suspected proximal venous occlusion, this study is now investigation of choice even in the asymptomatic patients where high predisposition is indicated by other symptoms. A 5MHz transducer proble detects a low pitched sound of venous flow which abolishes with compression. The main utility of this test in asymptomatic patients is concomitant delineation of venous anatomy, flow studies, characterisation of changes in the flow with augmentative muscular activity of the calf muscles, and assessment of effects of compression with the probe, since it may be used to obliterate the available lumen with firm pressure (Lensing et al. 1989). In cases of proximal vein thrombosis, this test yields 91% sensitivity and 99% specificity. However, as indicated by Polak et al. (1991), this test has limited diagnostic utility in distal DVT in the popliteal vessels (Polak and Wilkinson, 1991). Risk Factors and Timing Pregnancy in itself is a risk factor for DVT, and the incidence of this problem is reported to be 1 in every 1000 to 200 pregnancies, but lower incidence has also been reported (Andres and Miles, 2001). Apart from the physiologic changes in pregnancy, the duration of pregnancy also is a risk factor (Aquila, 2001). Other risk factors of pregnancy associated DVT are prolonged bed rest or immobility, obesity, innate coagulation disorders, advanced age at pregnancy. Some authors have reported that the DVT risk factors that may be influenced by pregnancy includes preeclampsia, prior cesarean delivery, varicose veins, multiparity, and associated or prior hemorrhage of pregnancy (Dixon-Townson, 2002). Special vigilance for asymptomatic DVT in pregnancy must be extended to pregnant women who had thromboembolic complications in prior pregnancies (Eldor, 2001). Given these factors and based on findings from studies, it may be stated that a pregnant woman is at risk of DVT at any point in her pregnancy and puerperium; however, Gherman et al. (1999) indicated that it is more prevalent in antepartum period (Gherman et al. 1999). Conclusion Clinically Doppler analysis combined with ultrasound or Duplex study is an appropriate screening test at any stage of pregnancy since ultrasound provides a real-time imaging and Doppler provides a flow analysis. However, the screening must be applied judiciously and interpreted cautiously since many asymptomatic pregnant women may have changes which may suggest ultrasonographic objective findings of DVT when none is there, and in some cases the DVT may appear in areas where this test is insufficient to detect a positive DVT. Given the crucial nature of diagnosis and its implications in early treatment and prevention of complications and given the devastating effects of treatment in the case of false positive diagnosis, it must be kept in mind that ultrasonography with Doppler is an extremely sensitive test for femoropopliteal system at any stage of pregnancy; however, for distal DVT and pelvic or iliac vein thrombosis repeat or serial tests must be included, if necessary augmented by other modalities of testing. For detection of cases, a high index of suspicion is necessary for the clinician and effective use of symptom scores and blood studies may be done to recommend the cases where screening and followup would be necessary. Randomized controlled trials are needed to establish a guideline. References Andres, RL. and Miles, A., (2001). Venous thromboembolism and pregnancy. Obstetrics and Gynecology Clinics of North America, 28(3), 613-630. Aquila, AM., (2001). Deep vein thrombosis. The Journal of Cardiovascular Nursing, 15(4), 25-44. Chan, WS. and Ginsberg, JS., (2002). Diagnosis of deep vein thrombosis and pulmonary embolism in pregnancy. Thromb Res; 107(3-4): 85-91. Chan, WS., Chunilal, SD., Lee, AY., et al., (2002). Diagnosis of deep vein thrombosis during pregnancy: a pilot study evaluating the role of D-dimer and compression leg ultrasound during pregnancy. Blood; 100:275a. Cogo, A., Lensing, AWA., Koopman, MMW., et al., (1998). Compression ultrasonography for diagnostic management of patients with clinically suspected deep vein thrombosis: prospective cohort study. BMJ;316:17-20. Cordts, PR. and Gawley, TS., (1996). Anatomic and physiologic changes in lower extremity venous hemodynamics associated with pregnancy; Blood; 24:763– 7. Dixon-Townson, D., (2002). Pregnancy-related venous thromboembolism. Clinical Obstetrics and Gynecology, 45(2), 363-368. Eldor, A. (2001). Thrombophilia, thrombosis and pregnancy. Thrombosis & Haemostasis, 86, 104-111. Frede, TE. and Ruthberg, BN., (1988). Sonographic demonstration of iliac venous thrombosis in the maternity patient. J Ultrasound Med 1988;(7): 33– 7. Gherman, RB., Goodwin, TM., Leung, B., Byrne, JD., Hethumumi, R., & Montoro, M., (1999). Incidence, clinical characteristics, and timing of objectively diagnosed venous thromboembolism during pregnancy. Obstetrics and Gynecology, 94(5), 731-734. Hull, RD., Raskob, GE., and Carter, CJ., (1990). Serial impedance plethysmography in pregnant patients with clinically suspected deep-vein thrombosis. Clinical validity of negative findings. Ann Intern Med; 112:663– 7. Kearon, C., Julian, JA., Newman, TE., et al., (1998). Noninvasive diagnosis of deep vein thrombosis. Ann Intern Med; 128:663-77. Lensing, AWA., Prandoni, P., Brandjes, D. et al., (1989). Detection of deep vein thrombosis by real time B mode ultrasonography. N Eng J Med; 320: 342-5. Perone, N., Bounameaux, H., and Perrier, A., (2000). Comparison of four strategies for diagnosing deep vein thrombosis: a cost-effectiveness analysis. Am J Med;110:33-40. Perrier, A., Desmaris, S., Miron, M-J., de Moerloose, P., Lepage, R., Slosman D., et al., (1999). Non-invasive diagnosis of venous thromboembolism in outpatients. Lancet;353:190– 5. Polak, JF. and O’Leary, DH., (1988). Deep venous thrombosis in pregnancy: noninvasive diagnosis. Radiology;(166):377– 9. Polak, JF. and Wilkinson, DL., (1991). Ultrasonographic diagnosis of symptomatic deep vein thrombosis in pregnancy. Am J Obstet Gynecol; 165: 625. Ray, JG. and Chan, WS., (1999). Deep vein thrombosis during pregnancy and the puerperium: a meta-analysis of the period of risk and the leg of presentation. Obstet Gynecol Surv; 54(4): 265-71. Scarvelis, D. and Wells, PS., (2006). Diagnosis and treatment of deep-vein thrombosis. Can. Med. Assoc. J.; 175: 1087 - 1092. Wells, PS., Lensing, AWA., Davidson, BL., et al., (1995). Accuracy of ultrasound for the diagnosis of deep venous thrombosis in asymptomatic patients after orthopedic surgery. A meta-analysis. Ann Intern Med;122:47-53. Read More