Correspondence
Venous Thromboembolic Disease and Pregnancy
N Engl J Med 2009; 360:638-640February 5, 2009
- Article
To the Editor:
In their review article on venous thromboembolic disease during pregnancy, Marik and Plante (Nov. 6 issue)1 recommend the use of compression ultrasonography as the initial test for pulmonary embolism. However, in nonpregnant patients, compression ultrasonography is not recommended by either the American Thoracic Society2 or the British Thoracic Society3 as the initial workup for pulmonary embolism in patients without leg symptoms because of the unacceptably low predictive value of positive findings (PPV). The PPV of compression ultrasonography is unknown in pregnancy and may be lower than that in nonpregnant women because leg swelling and low flow on compression ultrasonography without evidence of thrombosis are common in healthy pregnant women. Radiation exposure to the fetus from computed tomographic pulmonary angiography (CTPA) and lung ventilation–perfusion scanning is negligible. Reaching the exposure limit of 50,000 μGy that is considered acceptable by the National Council on Radiation Protection and Measurements4 in pregnancy would require 100 ventilation–perfusion scans or nearly 400 CTPAs.5 Pulmonary embolism during pregnancy is a serious disease that should be initially investigated with CTPA or ventilation–perfusion scanning, since these imaging techniques are low risk and have been validated in nonpregnant patients.
5 ReferencesLucia Larson, M.D.
Margaret Miller, M.D.
Niharika Mehta, M.D.
Warren Alpert Medical School of Brown University, Providence, RI 029051
Marik PE ,Plante LA . Venous thromboembolic disease and pregnancy. N Engl J Med 2008;359:2025-2033
Full Text | Web of Science | Medline2
American Thoracic Society
Web of Science | Medline3
British Thoracic Society Standards of Care Committee Pulmonary Embolism Guideline Development Group
CrossRef | Web of Science | Medline4
Medical radiation exposure of pregnant and potentially pregnant women. Report no. 54. Bethesda, MD: National Council on Radiation Protection and Measurements, July 1977.
5
Winer-Muram HT ,Boone JM ,Brown HL ,Jennings SG ,Mabie WC ,Lombardo GT . Pulmonary embolism in pregnant patients: fetal radiation dose with helical CT. Radiology 2002;224:487-492
CrossRef | Web of Science | Medline
To the Editor:
The algorithm in the article by Marik and Plante indicates that in patients with normal results on compression ultrasonography and chest radiography, either CTPA or ventilation–perfusion scanning should be performed, with no preference indicated as to which imaging technique should be used. The guidelines of the British Thoracic Society and a 2006 article by Matthews1 state that CTPA is a superior diagnostic tool for identifying pulmonary embolism, with radiation levels that are below the threshold for significant risk. Therefore, should not CTPA be the preferred method of investigation?
1 ReferencesShamik Dholakia, B.Sc.
Imperial College, London SW7 2AZ, United KingdomNarayanee de Mendonca, M.B., B.S.
Charing Cross Hospital, London W6 8RF, United Kingdom1
Matthews S . Imaging pulmonary embolism in pregnancy: what is the most appropriate imaging protocol? Br J Radiol 2006;79:441-444
CrossRef | Web of Science | Medline
To the Editor:
As obstetric internists, we agree that clinical prediction of venous thromboembolism is challenging, given the frequency of mild tachycardia, dyspnea, and leg edema during pregnancy. However, we must note that tachypnea in pregnancy is not physiologic and warrants further investigation. During pregnancy, minute ventilation increases through increased tidal volume without an alteration in respiratory rate.1
In pregnant patients in whom deep-vein thrombosis (DVT) is suspected and who have negative results on compression ultrasonography and negative D-dimer testing, we disagree that only clinical follow-up is sufficient. Although the results of the study by Chan et al.2 on the use of the SimpliRED assay and serial compression ultrasonography in pregnant women with a low overall rate of DVT are promising, the wide confidence intervals in that study do not yet support the systematic use of this test. Given the lack of validation for the suggested approach in this population of patients, we support serial compression ultrasonography and close clinical follow-up regardless of the results of D-dimer testing, especially since the use of single compression ultrasonography has not been validated for the evaluation of DVT in pregnancy.
2 ReferencesMeghan Hayes, M.D.
Ghada Bourjeily, M.D.
Karen Rosene-Montella, M.D.
Women and Infants' Hospital, Providence, RI 02905
meghan_hayes@brown.edu 1
Cugell DW ,Frank NR ,Gaensler EA ,Badger TL . Pulmonary function in pregnancy. I. Serial observations in normal women. Am Rev Tuberc 1953;67:568-597
Medline2
Chan WS ,Chunilal S ,Lee A ,Crowther M ,Rodger M ,Ginsberg JS . A red blood cell agglutination D-dimer test to exclude deep venous thrombosis in pregnancy. Ann Intern Med 2007;147:165-170
Web of Science | Medline
To the Editor:
With respect to restarting low-molecular-weight heparin after neuraxial anesthesia in obstetric patients, Marik and Plante state that the initiation of prophylactic low-molecular-weight heparin should be delayed for at least 12 hours after the removal of an epidural catheter. However, a position paper by the American Society of Regional Anesthesia (ASRA),1 which the authors cite, states that the delay should be 2 hours. Furthermore, Marik and Plante state that after neuraxial anesthesia, therapeutic low-molecular-weight heparin should be administered no earlier than 24 hours postoperatively and in the presence of adequate hemostasis, again citing the ASRA article. This recommendation is misleading, since it suggests that regional anesthesia is the reason for the 24-hour drug holiday, when in fact the ASRA article states that low-molecular-weight heparin should be withheld for 24 hours “regardless of anesthetic technique.”
1 ReferencesNir Hoftman, M.D.
University of California, Los Angeles, Los Angeles, CA 90095
nhoftman@mednet.ucla. edu 1
Horlocker TT ,Wedel DJ ,Benzon H , et al. Regional anesthesia in the anticoagulated patient: defining the risks (the second ASRA Consensus Conference on Neuraxial Anesthesia and Anticoagulation). Reg Anesth Pain Med 2003;28:172-197
CrossRef | Web of Science | Medline
Author/Editor Response
When confronted with a pregnant patient with a clinical suspicion of pulmonary embolism, one should start with bilateral compression ultrasonography, CTPA, or ventilation–perfusion scanning, depending on local availability and expertise. Although data from prospective studies involving pregnant patients with suspected thromboembolic disease are lacking, there is no reason why clearly abnormal results on compression ultrasonography would not establish a firm diagnosis of DVT. Furthermore, in a study of the use of negative results on compression ultrasonography during pregnancy or the postpartum period, Le Gal et al.1 found that no patient with a negative compression ultrasonogram had a thromboembolic event after 3 months of follow-up. However, any diagnostic test must be interpreted in the clinical context, and if any doubt exists, further diagnostic testing should be performed.
Dholakia and De Mendonca state that CTPA is a better diagnostic tool than ventilation–perfusion scanning. We cannot dispute this point except to note that many radiology departments have a strong preference for one imaging study or another, especially for use in pregnant patients. A survey of members of the Society of Thoracic Radiology reported that 53% perform CTPA as the initial study for pregnant women with suspected pulmonary embolism, whereas 30% begin with ventilation–perfusion scanning.2 Furthermore, recent data involving nonpregnant patients suggest that CTPA may be overly sensitive, detecting microemboli that may not be clinically significant.3
Hoftman is correct that the ASRA recommends the initiation of low-molecular-weight heparin no earlier than 24 hours postoperatively, regardless of the anesthetic technique used, and that the first dose of low-molecular-weight heparin should be delayed for at least 2 hours after an epidural catheter is removed.4 In our practice (and, we assume, in the vast majority of obstetric practices), the epidural catheter is removed at the conclusion of a cesarean delivery, so that a 24-hour postoperative delay in restarting therapeutic low-molecular-weight heparin is the same as a 24-hour postcatheter delay. The primary authors of the ASRA paper have more recently stated that thromboprophylaxis “should be held until at least 12 hours after vaginal delivery or epidural removal (whichever is later). After cesarean delivery, thromboprophylaxis should be held for at least 24 hours.”5
5 ReferencesPaul E. Marik, M.D.
Lauren A. Plante, M.D., M.P.H.
Thomas Jefferson University, Philadelphia, PA 19107
paul.marik@jefferson. edu 1
Le Gal G ,Prins AM ,Righini M , et al. Diagnostic value of a negative single complete compression ultrasound of the lower limbs to exclude the diagnosis of deep venous thrombosis in pregnant or postpartum women: a retrospective hospital-based study. Thromb Res 2006;118:691-697
CrossRef | Web of Science | Medline2
Schuster ME ,Fishman JE ,Copeland JF ,Hatabu H ,Boiselle PM . Pulmonary embolism in pregnant patients: a survey of practices and policies for CT pulmonary angiography. AJR Am J Roentgenol 2003;181:1495-1498
Web of Science | Medline3
Anderson DR ,Kahn SR ,Rodger MA , et al. Computed tomographic pulmonary angiography vs ventilation-perfusion lung scanning in patients with suspected pulmonary embolism: a randomized controlled trial. JAMA 2007;298:2743-2753
CrossRef | Web of Science | Medline4
Horlocker TT ,Wedel DJ ,Benzon H , et al. Regional anesthesia in the anticoagulated patient: defining the risks (the second ASRA Consensus Conference on Neuraxial Anesthesia and Anticoagulation). Reg Anesth Pain Med 2003;28:172-197
CrossRef | Web of Science | Medline5
Kopp SL ,Horlocker TT . Anticoagulation in pregnancy and neuraxial blocks. Anesthesiol Clin 2008;26:1-22
CrossRef | Medline
