Tag Archives: pregnancy

How Much Fetal Radiation Exposure In Imaging Studies?

I periodically publish a chart that shows how much radiation exposure our patients get from various trauma imaging studies. For reference, here it is:

Test Dose (mSv) Equivalent background
radiation
Chest x-ray 0.1 10 days
Pelvis x-ray 0.1 10 days
CT head 2 8 months
CT cervical spine 3 1 year
Plain c-spine 0.2 3 weeks
CT chest 7 2 years
CT abdomen/pelvis 10 3 years
CT T&L spine 7 2 years
Plain T&L spine 3 1 year
Millimeter wave
scanner (that hands
in the air TSA thing at
the airport)
0.0001 15 minutes
Scatter from a chest
x-ray in trauma bay
when standing one 
meter from the
patient
0.0002 45 minutes
Scatter from a chest
x-ray in trauma bay
when standing three 
meters from the
patient
0.000022 6 minutes

One of the issues that trauma professionals gnash our teeth about is how much radiation the baby gets when we perform these studies on pregnant women. Well, here is just what you need. Another chart! In order to avoid confusion, I will list effective doses to the fetus in milligrays (mGy), which is how much radiation is deposited in a substance. This is a little confusing, since doses are frequently listed in millisieverts which takes the specific organ and type of radiation into effect. In general, these two units are very similar for x-rays.

A useful rule of thumb is that if the fetal dose is less than 50 mGy during any trimester, the risk of an abortion or fetal malformation is about the same as from other risks to the pregnancy. The American College of Radiology notes that exposures less than 100 mGy are “probably too subtle to be clinically detectable.”

To help in your clinical decision making, I’ve added some extra information to the table regarding fetal exposure:

Test Adult Dose (mSv) Fetal Dose (mGy)
Chest x-ray 0.1 negligible
Pelvis x-ray 0.1 negligible
CT head 2 <1
CT head and C-spine 4 10
CT chest 7 <1
CT abdomen/pelvis 10 25
Pan Scan (CTA chest, abdomen, and pelvis) up to 68 up to 56
CT pulmonary angiogram up to 40 <1

Bottom line: We still have to think hard about how we image pregnant patients! There are some alternatives available to us, including the good old physical exam, conventional x-rays, and ultrasound. MRI is possible, but is a pain in the ass for many reasons. 

CT of the head and cervical spine are fine for both mother and baby, and non-contrast imaging of the torso is within accepted limits of fetal exposure. However, the whole point of the torso scan in CT is to identify critical injuries that may lead to exsanguination like solid organ and aortic injuries. In general, those scans should always be ordered with contrast. 

If clinical suspicion is high, it may be necessary to order these higher-dose studies anyway. If the mother has an unrecognized and potentially fatal injury, the baby will not survive either. There are many, many permutations of injuries and diagnostics. These cases will put your clinical judgment to the test, for sure!

References:

  • Imaging Pregnant and Lactating patients. RadioGraphics 35:6, 1751-1765, 2015.
  • Imaging of the pregnant trauma patient. RadioGraphics 34:3, 748-763,2014.
  • Fetal doses from radio logical examinations. Br J Radiol;72(860): 773–780, 1999.

The Peri-Mortem C-Section

The perimortem C-section (PMCS) is a heroic procedure designed to salvage a viable fetus from a moribund mother. Interestingly, in some mothers, delivery of the fetus results in return of spontaneous circulation.

The traditional teaching is that PMCS should be started within 4-5 minutes of the mother’s circulatory arrest. The longer it is delayed, the (much) lower the likelihood that the fetus will survive.

The reality is that it takes several minutes to prepare for this procedure because it is done so infrequently in most trauma centers. Recent literature suggests the following management for pregnant patients in blunt traumatic arrest (BTA):

  • Cover the usual BTA bases, including securing the airway, obtaining access and rapidly infusing crystalloid, decompressing both sides of the chest, and assessing for an unstable pelvis
  • Assess for fetal viability. The fundus must measure at least 23 cm.
  • Assess for a shockable vs non-shockable rhythm. If shockable, do two cycles of CPR before beginning the PMCS. If non-shockable, move straight to this procedure.

Bottom line: Any time you receive a pregnant patient in blunt arrest, have someone open the C-section pack while you assess and try to improve the mother’s viability. As soon as you complete the three tasks above, start the procedure! You don’t need to wait 4 minutes! And by the way, this is usually a procedure for surgeons only. They have the speed and skills to get to the right organs quickly. If unavailable, do what you need to do but recognize that the outcome may be even worse than it usually is.

Trauma In Pregnancy 5: C-Section – When?

The perimortem C-section (PMCS) is a heroic procedure designed to salvage a viable fetus from a moribund mother. Interestingly, in some mothers, delivery of the fetus results in return of spontaneous circulation.

The traditional teaching is that PMCS should be started within 4-5 minutes of the mother’s circulatory arrest. The longer it is delayed, the (much) lower the likelihood that the fetus will survive.

The reality is that it takes several minutes to prepare for this procedure because it is done so infrequently in most trauma centers. Recent literature suggests the following management for pregnant patients in blunt traumatic arrest (BTA):

  • Cover the usual BTA bases, including securing the airway, obtaining access and rapidly infusing crystalloid, decompressing both sides of the chest, and assessing for an unstable pelvis
  • Assess for fetal viability. The fundus must measure at least 23 cm.
  • Assess for a shockable vs non-shockable rhythm. If shockable, do two cycles of CPR before beginning the PMCS. If non-shockable, move straight to this procedure.

Bottom line: Any time you receive a pregnant patient in blunt arrest, have someone open the C-section pack while you assess and try to improve the mother’s viability. As soon as you complete the three tasks above, start the procedure! You don’t need to wait 4 minutes!

Trauma In Pregnancy 4: Imaging

Everyone worries about imaging pregnant patients. As with most medical tests, it always boils down to risks vs benefits. What are the chances of causing mutations or cancers or a spontaneous abortion, and what is the risk of missing a critical injury? In general, reasonable studies involving a fetus at just about any point in gestation won’t cause major problems. At least as far as we know. What is not clear are the longer term, hard to measure effects. So the general philosophy should be to order just what you absolutely need, and shield the fetus during any studies other than of the abdomen/pelvis.

Now, to put these numbers into perspective, have a look at this list of delivered doses from common studies. The table above is listed in milliGrays, and this one is in milliSieverts. These are roughly comparable, except that the former is a measure of radiation dose absorbed, and the latter measures radiation delivered.

Bottom line: Think hard about the imaging you really need. If you generally do this for all patients, you probably won’t change your practice in pregnant women. Don’t worry about chest and pelvic x-rays. Shield the fetus for anything not involving the abdomen/pelvis. For major torso trauma, you probably will need CT of the chest/abdomen/pelvis. If so, do it right. Order with contrast so you don’t get substandard images that need to be repeated.

Trauma In Pregnancy 3: Tips & Tricks

Here is a list of practical tips for trauma professionals from prehospital and beyond:

  • Apply supplemental oxygen from the get-go, in the field if possible
  • Start an IV or IO and begin crystalloid infusion immediately
  • Bump the patient to her left. This is most easily done with the spine board in place. Just put a rolled up towel under the right side of the board.
  • Quickly estimate how pregnant the patient is if she can’t tell you. Use the fundal height diagram below. Key measurements to remember:
    • Umbilicus = 20 weeks: entering the possible viability range if delivered emergently
    • Xiphoid = approaching full term

  • If the patient is 20 weeks+ pregnant, only transport to a trauma center (Level I or II).
  • At the hospital, reassess fundal height to more accurately estimate viability
  • If the fetus may be viable (23-24 weeks), call OB to the resuscitation area. But remember, they have nothing to offer until the trauma team secures the safety and stability of the mother. So don’t let them in the room until you have finished your entire evaluation.  Nothing they can do (e.g. monitor) is helpful during the acute phase of the resuscitation.
  • Once the mother is stabilized, assess fetal heart tones and apply monitors for fetal heart rate and maternal contractions.
  • Add coag studies to your lab panel. Fetal and placental injury can cause clotting problems.
  • Consider giving Rhogam in all major trauma cases if the mother is Rh negative
  • Obtain a KB test to look at the amount of fetal blood in the maternal circulation. Why do this if you are going to give Rhogam anyway? Answer: sometimes the amount of fetal blood leakage is greater than that covered by a single vial of Rhogam.
  • Plan your imaging intelligently. The next section covers this topic in more detail.
  • If needed, chest tubes should be inserted 1-2 intercostal spaces higher than usual.
  • The life-saving tetanus shot is safe in pregnant patients.