CTPA and PEs - what use?
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CTPA and PEs - what use?
Chat about radiology with radiologists and those who want to get into the speciality
Another notorious post from The Medical Registrar on Facebook... "But it's clearly a pneumonia on the CXR.." "No it's not. Get a CTPA" "But the radiologist will get cross...." "Get a CTPA" "But he's o
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Forums » Open clinical » Radiology » CTPA and PEs - what use?
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CTPA and PEs - what use?
posted at 27/10/2011 12:20 PM BST
on bmj.com
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Posts: 322
First: 27/10/2011 Last: 24/5/2013 |
Another notorious post from The Medical Registrar on Facebook... "But it's clearly a pneumonia on the CXR.." "No it's not. Get a CTPA" "But the radiologist will get cross...." "Get a CTPA" "But he's on Clexane" "Get a CTPA" CTPA report: pulmonary embolus Lesson: never argue with the big dog, cos the big dog is always right..... What do we actually know about the fate of untreated PEs, especially since there must be a large number that sneak under the radar of the clinical team (we often see them incidentally)? Can this be balanced against the risks of anticoagulation and radiation exposure? It's all very well to say that we over-investigate (which I think that we do), but do we have the knowlegde or the stones to hold back and say, is the CTPA actually going to make a difference? Good luck, big dog...I don't envy being at your end of the phone! |
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Re: CTPA and PEs - what use?
posted at 27/10/2011 3:57 PM BST
on bmj.com
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Posts: 1181
First: 19/4/2010 Last: 23/5/2013 |
Great topic. PE - the most over-diagnosed, and under-daignosed disease in medicine. I think we have to have a very high suspicion with PE. It's very easily missed, and the consequences of missing the diagnosis are myriad, and of significant consequence. 1. PE is ofter the herald of malignancy. Missing the PE means missing the trigger to look for the underlying, potentially resectable/curable cancer, and that's disappointing. 2. Chronic pulmonary thromboembolic disease is one of the few treatable causes of pulmonary hypertension. Treating the first PE may stave of the development of the disease, picking up the "n"th PE allows a diagnosis, and referral for endarterectomy. 3. PE kills people, pure and simple. We see large clots, small clot, multiple clots. What we don't see are the PEs that cause sudden death, out in the community. Small clot missed today, might mean huge clot causes death tomorrow. As to over investigating, that's part of the deal. One of my senior colleagues has always maintained that we whould have a pick up rate on CTPA or V/Q of between 15 and 25 %. Any lower, we're over investigating, and higher and we're missing some. We audit our practice regularly, and we're about 18% at last check. Another interesting point is the choice between CTPA and V/Q. I think most chest physicians these days would rather get a CTPA - it gives near HRCT quality images of the lung parenchyma, a reasonable assessment of the mediastinum, and some sort of assessment of the right ventricle. But the payoff is 8 mSv radiation dose (in our unit)..... Great post, thanks.
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Re: CTPA and PEs - what use?
posted at 27/10/2011 4:50 PM BST
on bmj.com
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Posts: 322
First: 27/10/2011 Last: 24/5/2013 |
Some really useful points, DundeeChest. This is quite illuminating for when it comes to approaching all those phone and e-requests, appreciating a mindset of the requesting physician that may not be familiar to non-respiratory radiologists. However, I can't help but feel that 75-85% negative examination rate is a significant burden of radiation for "SOB ?cause" or "chest pain - ?PE". I presume that the 'optimal window' for pick-up rate is set by audit practice? While I would also favour CTPA over V/Q(dot) on account of more useful information, just like CT of the abdomen and pelvis for the surgeons, CTPA appears to have slipped effortlessly into the role of a diagnose-all that is open to some misuse... (I wonder what the diagnostic equivalent of a panacea might be!?) |
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Re: CTPA and PEs - what use?
posted at 27/10/2011 5:47 PM BST
on bmj.com
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Posts: 177
First: 23/12/2010 Last: 26/4/2013 |
Thanks Dundee and Hip radiologist for highlighting the importance of CTPA. CT does have superior ability in the detection of PE. In life threatening situations, one does not consider the dose of radiation as a priority... in my opinion..... Joe. |
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Re: CTPA and PEs - what use?
posted at 27/10/2011 5:49 PM BST
on bmj.com
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Posts: 1181
First: 19/4/2010 Last: 23/5/2013 |
I totally accept that the CTPA has become the get out of jail free test for the acute physician. We do try to apply a little logic to things, and as chest physicians, we see patients a little further down the conveyor belt, when the Abx haven't worked, and they're still SOB, and PE moves up the differential. To be fair, our radiologists are always very helpful with *our* requests for CTPA. Interestingly, the AMU hit rate for PE has been below 10% ...... |
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Re: CTPA and PEs - what use?
posted at 31/10/2011 3:13 PM GMT
on bmj.com
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Posts: 8
First: 31/10/2011 Last: 4/11/2011 |
This is an interesting discussion about the number of CTPAs performed in the acute setting and how many actually reveal any evidence of PEs. The opening dialogue is all to familiar, and in my FY1 year, I used to spend early morning wondering why we need a CTPA and the rest of the morning convincing myself aswell as the radiologist. |
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V/Q
posted at 1/11/2011 4:19 PM GMT
on bmj.com
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Posts: 1181
First: 19/4/2010 Last: 23/5/2013 |
When to V/Q and when to CTPA. I think most chest physicians would rather have a CTPA every day of the week, and twice on Sundays; the extra information afforded is invaluable in many cases. The V/Q requires expert assessment, and in skilled hands is an excellent tool. We are lucky enough to have a great team of nuclear medicine docs to report out V/Q scans. One area in which a V/Q trumps a CTPA is the assessment of chronic PE, and in situ thrombosis (so called peripheral pruning) - the CTPA will only show current clot, and not poor peripheral perfusion indicative of PEs of various ages. I think the new PE investigation guidelines will suggest CTPA as first line investigation to rule out/in acute PE.
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Re: CTPA and PEs - what use?
posted at 4/11/2011 5:54 PM GMT
on bmj.com
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Posts: 322
First: 27/10/2011 Last: 24/5/2013 |
I agree with DundeeChest on the benefits of CTPA over V/Q, but it should be remembered that the pre-test probability will also affect the diagnostic accuracy of the V/Q scan, something that is not any easy concept to understand, let alone remember in the heat of the request. The following gives an idea of how the diagnostic likelihood of PE from V/Q scans changes given the different probabilities matched with the V/Q result.
 From a radiology perspective, CTPA is certainly a less specialised and more available test. Currently we generally don't perform CTPAs out of hours unless there is a contra-indication to anticoagulation, otherwise we would be swamped all night. This is probably not going to be an acceptable excuse not to perform the CTPA at night in a few years time! V/Q scans also rely on the supply of 99m-technetium used in the perfusion part of the scan, being attached macro-aggregated albumin molecules which lodge in the capillary bed of the lung (roughly 1 in every 1000 - not a pleasant thought, but the maths does keep you alive). 99m-Tc (half-life 6 hours) is the decay product of 99-molybdenum (half-life 66 hours) and produced by a generator that is replenished form suppliers every fortnight, so it is also possible that nuclear med have run low on 99m-Tc and so CTPA it is after all... |
Forums » Open clinical » Radiology » CTPA and PEs - what use?
