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Cta Vs. V/q Scan in the Pregnant Patient

A 25 y F g1p0 @8wks pregnant presents to ED complaining of SOB. Clinical suspicion for PE with a positive dimer to 0.68.  Assuming lower extremity dopplers and chest x ray are unremarkable. How will you further workup this patient?

CTA or V/Q Scan?

For us recent med school grads the new teaching has been that V/Q scanning produces a greater radiation risk to the fetus. While CTA does deliver a slightly lower radiation dose to the fetus in comparision to V/Q scanning (0.003 to 0.131 mGy versus 0.32 to 0.74 mGy), according to the National Council of Radiation Protection and Measurements the risk of radiation-associated abnormalities is negligible at levels below 50 mGy. Additionally, the maternal dose of radiation for CTA vs V/Q is 7.3 mGy vs 0.9 mGy respectively and V/Q scanning results in 150 fold less irradiation to breast and lung tissue.

In addition, the rate of non-diagnostic imaging increases in pregnant patients undergoing CTA and decreases in patients undergoing V/Q. CTA scanning is thought to be more frequently non-diagnostic in pregnancy because there is an increase pressure from the IVC (esp. in the 3rd trimester) which interrupts blood flow from the SVC (where contrast enters). V/Q scans improve because pregnant patients are generally younger and healthier.

V/Q scans in pregnant patients were found to be non-diagnostic (i.e. moderate probability scans) 7-25% of the time whereas CTA imaging in pregnant patients was found to be non-diagnostic of PE in 17-28% of patients.

Comparative analysis between the 2 imaging modalities has shown varying results, but overall, studies indicate V/Q is non-diagnostic of PE with the same or less frequency than CTA.

It is important to realize that V/Q scans are used strictly to determine the presence or absence of PE, while CTA may identify numerous different pathologies.

Thus, while the preference of many clinicians is CTA, which may well be appropriate, evaluate the risks and give consideration to V/Q scan.  Also important to keep in mind is that this information is with respect to chest scans and the work up of PE in a pregnant patient should likely begin with lower extremity dopplers.

An Old but Still Ongoing Arguement

Asking an anesthesiologist or EM doc their choice of paralytic can spark heated debate.  What do you prefer?

-depolarizing agent
-30-60 sec onset
-8-15 min duration
-adverse reactions: bradycardia, hyperK, fasciculations, malignant hyperthermia, increased intracranial pressure
-contraindications: herperK, burns or crush injuries, upper motor neuron disorders

-non-depolarizing agent
-At 1.2 mg/kg; no difference in time to onset
-45-60 min duration
-contraindications: roc allergy

Proponents of succinylcholine often point to its short duration of action saying that if things go wrong during RSI you only have to bag the patient for 10 min for them to breath spontaneously. While that may be an option in patients undergoing elective surgeries in the OR, this is rarely the case in an ED population. To quote Chris Nickson of Life in the Fast Lane, “If you are performing RSI on a patient and it is feasible to wake them up if things go haywire, then you probably shouldn’t have been doing the RSI in the first place!”

Blow by Oxygen

You’re rotating in the RICU and while there one of your patients develops respiratory distress requiring intubation. As you are preparing your equipment you notice that the intern on the team, who is trying to be helpful, is holding the BVM above the patients face to provide, “blow by oxygen.” Why is this not a beneficial preoxygenation strategy? Continue reading “Blow by Oxygen” »

Tylenol for Low Back Pain: No Better Than Placebo

This recent meta-analysis in the BMJ found that paracetamol (acetaminophen) was no better than placebo for the treatment of low back pain.   Continue reading “Tylenol for Low Back Pain: No Better Than Placebo” »

Peek Through the Orbit

32 yo overweight female presents with a headache.  This headache is similar to prior headaches, which she gets frequently.  The rest of her story seems consistent with a migraine and her physical exam, including a through neuro exam, is normal.  However, you still feel concerned because she’s in the right demographic for idiopathic intracranial hypertension.  You think the optic disc looked okay, but if you’re anything like me you’re not super confident in that assessment.  What is another modality you could use to assess for increased intracranial pressure?  How good of a test is it?  Continue reading “Peek Through the Orbit” »

Leslie Pendery, MD