Kellogg Student awarded Gillian Nicholls Prize

July 6, 2020

Congratulations to Kellogg student, Neville Gibbs, on receiving this year’s Gillian Nicholls Prize for his dissertation, Diagnostic accuracy of viscoelastic point of care identification of hypofibrinogenaemia in cardiac surgical patients: A systematic review.

The Gillian Nicholl Prize is awarded by the Department of Evidence-Based Healthcare, to a student whose dissertation they deem to be outstanding.

Clinical Professor Neville Gibbs, who is an anaesthetist in his home country of Australia, and a part-time student at Kellogg, recently completed his MSc in Evidence-Based Health Care. On receiving the Gillian Nicholls Prize he said, “For me, being awarded the Gillian Nicholls Prize was a source of great surprise and delight, which I will always cherish. I hope it will be a source of encouragement to all others undertaking an MSc dissertation at a later stage in their career.”

The panel said of Neville’s dissertation, “The review assessed the evidence for the accuracy of a rapid test performed by anaesthetists during surgery for cardiac patients to assess blood clotting factors and prevent excessive bleeding. This is an important and relevant question for clinical practice and the dissertation provided a comprehensive assessment of the evidence.”

Neville summarises his dissertation below:

Diagnostic accuracy of viscoelastic point of care identification of hypofibrinogenaemia in cardiac surgical patients: A systematic review

Normal blood clotting is vital during cardiac surgery to prevent excessive bleeding from the heart and major blood vessels.  Fibrinogen is an important component of normal blood clot.  Unfortunately, fibrinogen levels may fall during cardiac surgery, exposing patients to a risk of dangerous bleeding.  Low fibrinogen levels (also known as hypofibrinogenaemia) can be corrected rapidly by the administration of additional fibrinogen, but identifying low levels using standard laboratory tests takes 45 minutes or more.  During this time further excessive bleeding could occur.  In contrast, viscoelastic point of care fibrinogen tests have the advantage of providing results within 15 minutes, allowing earlier intervention and correction of fibrinogen levels.  However, it is not known whether they are as accurate as standard laboratory tests.  This is a problem because falsely low fibrinogen levels (a false positive result) could prompt unnecessary fibrinogen replacement, which has its own costs and risks.  Worse, a falsely normal fibrinogen level (a false negative result) could leave patients exposed to an unnecessary risk of continued bleeding.  The aim of my study was to sift through all relevant published research on the accuracy of viscoelastic point of care fibrinogen tests in a methodical way to answer the question: “Are viscoelastic point of care tests as accurate as standard laboratory tests for identifying hypofibrinogenaemia in cardiac surgical patients”.

I used a broad search strategy across seven electronic databases and identified 576 articles on viscoelastic point of care tests.  Of these, 81 involved cardiac surgery.  Careful screening of these 81 identified nine articles related to my search question.   Seven were on a device called a ROTEM and two were on a device called a TEG.  In total the studies included about 1800 patients.  None were high quality, in that they all had some question over the reliability of their results.  The studies were mostly too diverse for their results to be reliably combined.

When assessed against standard laboratory tests, the false positive rates for the viscoelastic tests for identifying hypofibrinogenaemia in clinically relevant scenarios across the nine studies ranged from 19 to 58%, and the false negative rates from 0-26%.  Importantly there were no obvious clues as to which patients would have higher vs lower false positive or negative rates.  These findings indicate that the viscoelastic tests are not accurate enough to ‘replace’ standard laboratory tests in cardiac surgical patients, particularly when there is no time pressure to make decisions about fibrinogen replacement.  This is because using viscoelastic point of care tests alone to guide fibrinogen replacement could result in unnecessary fibrinogen replacement in up to 58% of patients, and in up to 26% of patients, dangerous hypofibrinogenaemia could be missed.   Nevertheless, there may still be an important role for viscoelastic point of care fibrinogen tests in cardiac surgical patients.  This is because sometimes it is not possible to wait 45 minutes before making a decision on fibrinogen replacement.  For example, a patient may be bleeding too briskly to safely permit this delay.  In these circumstances, viscoelastic point of care tests may have a pivotal role: the alternative would require making decisions about fibrinogen replacement based on clinical findings alone.  In all nine studies, positive viscoelastic test results increased the likelihood that hypofibrinogenaemia was present.  Similarly, in all nine studies, a negative result decreased the likelihood of hypofibrinogenaemia being present.  In other words, while not being as accurate as standard laboratory tests, the viscoelastic point of care tests still provided useful information on the likelihood of hypofibrinogenaemia to help guide decision-making on fibrinogen replacement.

In conclusion my study found that there are very few published studies, and no high quality published studies, on the accuracy of viscoelastic point of care tests of fibrinogen in cardiac surgical patients.  The results of the few studies performed so far indicate that viscoelastic point of care tests of fibrinogen are not sufficiently accurate to replace standard laboratory tests when it is safe to wait the requisite 45 minutes or more for a result.  However, they may have an important role in patients who are bleeding briskly, and who require a more rapid decision about fibrinogen replacement than would be possible using standard laboratory tests.

You can read more about Neville and his decision to pursue the MSc in Evidence-Based Healthcare on the Oxford Department for Continuing Education‘s website: www.conted.ox.ac.uk/profiles/student-spotlight-neville-gibbs