POTCAST: Can you stop the clot?

Spring is here in Yorkshire. The weather is warming up, the evenings are lighter and the bike rides are getting slightly longer after a winter of ‘strictly business’ commutes to work.

This month’s JC was a collaborative effort with a great mixed group of attendees – we had ED docs, one of our Ortho colleagues, some of the ENPS and the DVT nurses joined us too, so the field was broad, but the EBM talk was awesome!

And what got them so excited and enagaged? A paper on a sexy topic like REBOA? Major trauma haemorrhage control? Nope…….

VTE prevention in patients immobilised in a plaster.

FOAMed is criticised by some for focusing on the niche, resus room based topics, that only affect small numbers of patients, not this. How many patients do you immobilise for a lower limb injury in your department every week?

Title of Paper: Thromboprophylaxis after knee arthroscopy and lower limb casting.

Published: NEJM 2017

Your next patient is a 34 year young man who has rolled his ankle during a football match (or soccer if you’re of a north american persuasion) his x-ray shows an undisplaced ankle fracture, he’s in lots of pain and can’t weight bear. You decide to immobilise him in a lower limb back-slab and send him off to fracture clinic on some crutches. You’re a dutiful sort and have read the NICE and RCEM guidance on lower limb immobilisation and you wonder about what the evidence says about the need to give him thromboprohylaxis to reduce his risk of VTE whilst he’s immobilised.

Clinical Question: In lower risk patients who are immobilised in a plaster cast in ED for a week, does thromboprophylaxis reduce the risk of symptomatic VTE (venous thrombo-embolism).

Population: Adults presenting to ED with a lower limb injury and immobilised in a plaster cast for a week
Intervemtion: Prophylactic LMWH
Control: no treatment
Outcome: Symptomatic VTE in 3 months.

The intervention: This was an open label trial using Dalteparin at 2500units or Nadroparin 2850units SC, the control arm got no medication. The LMWH was given for the full period of immobilisation including a first dose in ED.

Generalisability This was a multicentre blinded (outcome evaluation) controlled trial, with block randomisation and randomisation was then done by a computer generated software minimising the risk of bias. The trial was run across 10 sites in the Netherlands. A power calculation was done which was powered to detect an 85% relative decrease in symptomatic VTE from a predicted control baseline of 2% incidence. There are a few issues with this trial here we felt – the level of difference they were trying to detect was huge and our local expert (Steve Goodacre) wondered if you would only such effect at treatment dose of Dalteparin. A second issue is around their dosing – we couldn’t work out why such a low dose of Dalteparin was given and none of us have any hands on experience of Nadroparin. We currently are advised to give 5000 units of Dalteparin for VTE prophylaxis at our trust so worry that these findings arent really applicable to our current set up. What are you using at your shop?

Patients: The patients are those at lower risk of VTE (we would assume) in that they excluded those with a previous VTE and those who were pregnant, they also excluded those who were on anticoagulants or couldnt take LMWH. They also excluded those who had insufficient mental or physical ability to complete the trial – we were a little bit worried about this as this seemed ‘wooly’ and open to bias, and the number of screened patients is not clear in the right up and there doesn’t seem to be a CONSORT diagram. If you look at those who were included the spread was equal amongst the groups, but a high proportion of people in work and the mean age was 46 (approx). This made us worry that they excluded those who were elderly or who may be likely to have reduced mobility – and a potentially higher risk of VTE.

The reasons for immobilisation were broad ranging from fractures of the ankle, achilles tendon rupture and as far as ‘antalgic gait’ and metatarsal fractures. its not clear with these injuries the number or type of MT fractures, but one of our friendly local orthopods who came along to JC (@jamestoml1) said this was interesting as a few days or a week down the line in fracture clinic these guys can look wildly different – using the example of an Achilles rupture being massively swollen, and incredible painful where as some ankle fractures can quite comfortable move their foot up and down in the POP. We also worried that the MT fractures, if isolated and stable may have been ambulated in ED with a boot at our place – we try and get people moving asap.

Results: They enrolled and analysed around 720 patients in each group and found no clinically significant difference between the treatment and control arms, with an Absolute risk reduction of 0.4% (95% CI -1.8% to 1%) which if you wanted to work out is an NNT of 250. Now they found no significant harm events in either group. The way they followed patients up was interesting – they used patient instruction and questionnaires to find out whether they ha symptoms of a VTE and this was interesting as in an open label trial such as this one may hypothesise that the patient who had the treatment may be less likely to seek help for and report ‘that niggle at the back of the leg’ compared with those who knew they had no treatment. Given the lack of difference in the two arms one could possible assume that this didn’t happen, or that the effectiveness of treatment was even less.
A criticism of previous work on the topic is that the VTE that was being detected was asymptomatic clots on routine scanning and the approach in this trial whilst open to bias is probably as real world and pragmatic a you can be – tell the patient the symptoms of badness and ask them to let you know if they get it.

All in all this paper probably doesn’t answer the question of VTE prophylaxis for me in its entirity I have more questions now I think than before I read it, but its certainly food for thought. I plan to email the author to ask about the dosing regime for dalteparin and have a talk with our local hameatologists too around the topic. I’ll let you know what I find out…..

As always thanks for taking the time to read my summary any feedback will be gratefully received….

One minute wonder can be foundpotcast

Keep fighting the good fight

Chris

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