Pulmonary Embolism - PE - Evaluation in the pregnant patient
Investigation for pulmonary embolus (PE) in pregnancy is a complicated area. It is well know that PE is the leading cause of death in pregnancy in the developed world1. The pregnant patient fulfils all of Virchow’s triad-venous stasis, vessel damage and hypercoagulability. Difficulty and confusion arises in the work up of PE in the pregnant patient due to 3 things:
The normal physiological changes in pregnancy; dyspnoea, tachycardia and leg swelling are also symptoms that a patient with a PE can present with.
The pre-test probability score, Wells Criteria2, cannot be used in a pregnant patient as they were excluded from the analysis group for criteria validation.
The d-dimer will start to rise in the second trimester and remain elevated for 4-6 weeks post-partum.
If a PE is suspected it is important to definitively diagnose, as management of a PE during pregnancy needs to include choice of anticoagulation, mode of delivery and consideration of prophylaxis in future pregnancies. There continues to be ongoing debate in regards to the optimal way to investigate the pregnant patient.
The PIOPED II study3 made the following recommendations for pregnant patients:
D-dimer with clinical assessment should be obtained.
If d-dimer is positive, venous ultrasound is recommended before imaging tests with ionizing radiation.
69% of PIOPED II investigators recommend pulmonary V/Q scan and 31% recommend a CT angiogram.
Also included here is an algorithm for pulmonary embolism in pregnancy, developed by Diagnostic Imaging Pathways, Western Australia.
The following is a proposed approach to PE work up in the pregnant patient, drawing on the information there is to date:
What is your pre-test probability or Gestalt? If you have a pregnant patient and PE is the most likely diagnosis then place the patient as high risk and progress to imaging (see below).
If the signs and symptoms are suggestive of PE but there are other diagnosis equally likely and the patient is in first trimester perform a D-dimer. If this is negative you can stop.
If the patient is high risk or has a positive d-dimer you should now perform a chest x-ray. You will need this to aid in the choice between V/Q and CTPA. It also may show an area of consolidation or a pneumothorax.
Prior to consideration of V/Q or CTPA perform bilateral venous dopplers. If this is positive you can stop here and treat for PE.
V/Q or CTPA? The main concern is radiation risk for both mother and fetus. The risk of death from an undiagnosed PE is much higher than the risk of malignancy due to radiation. When considering V/Q as an option also be aware that you may still need to go on to do a CTPA if inconclusive.
The Fetus: General consensus is that radiation exposure of 0·1 Gy during gestation is the threshold beyond which induction of congenital abnormalities is possible. This is estimation and there are no supporting studies validating it. Both V/Q and CTPA fall well below 0.1 Gy with V/Q scan having a slightly higher dose than CTPA1, 2. Suggestions for reducing fetal exposure from technetium during the V/Q scan include good hydration of mother prior to scan and immediate voiding post scan or placing a catheter. The iodine contrast used during CTPA has a theoretical risk to the fetal thyroid although there are no studies investigating this.
The Mother: CTPA exposes breasts to a much higher radiation dose compared V/Q scan. Using Bismuth breast shields can reduce the dose of radiation. The radiation dose of a V/Q scan can be minimized by using a half-dose perfusion scan and only proceeding to ventilation imaging if a defect is identified on the perfusion scan.
If chest x-ray is normal the patient should undergo a half-dose perfusion scan. If the chest x-ray is abnormal the patient should undergo a CTPA.
Opinion of note and possible controversy is by Dr Jeff Kline, Director of Research, Department of Emergency Medicine, Carolinas Medical Centre, Charlotte, North Carolina. He is the man behind the PERC rule4, 5 and countless other studies on pulmonary embolus.
The risk of pulmonary embolus in the non-pregnant female risk is 1 in 100,000 increases to 1 in 10,000 in pregnant age-matched females.
From Kline’s own work, 60% of healthy patients in normal pregnancy will have a raised D-dimer. He proposes using the PERC rule, adapted for normal physiological change in heat rate during pregnancy, in combination with an altered D-dimer threshold to risk stratify pregnant patients.
First trimester: Modified PERC, heart rate >105 and D-dimer threshold 50% higher than normal cut-off.
Second trimester: Modified PERC, heart rate >105 and D-dimer threshold 100% higher than normal cut-off.
Third trimester: Modified PERC, heart rate >105 and D-dimer threshold 125% higher than normal cut-off.
The important thing to remember is that if you think of PE as a diagnosis you need an approach to confidently exclude or diagnose. If there is any concern or ongoing confusion involve Radiology, Respiratory and Obstetrics/Gynaecology for further discussion. Remember to involve the mother in the decision process. Refer to this WA Diagnostic Imaging Pathways, for more information on imaging during pregnancy.
The DiPEP study looked at biomarkers and VTE in pregnant women and concluded that D-dimer among other biomarkers were not reliable to rule VTE in or out in pregnancy, and this refutes to some extent Jeff Kline's work. It is suggested that pregnant patients with suspected PE should be manged in discussion with your senior referral partners.