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Pickering V Cambridge University Hospitals NHS Foundation Trust: Where Expert Witnesses Make All The Difference

By Flora McCabe, Head of Advocacy and Risk Management Healthcare, Senior Vice President, Lockton Companies LLP, London EC3A 7AG

T: 0207 933 2516 E:

‘Wisely and slow. Those that stumble run fast’ (Romeo and Juliet, Act II iii 101). At last year’s conference, I focused on cases where expert witnesses had failed in their duties to the Court. Unfortunately, despite much recent focus on how to improve expert witness reports, we continue to see examples of expert witnesses who, if not in actual breach, certainly leave much to be desired in terms of their ability to perform as credible expert witnesses, often appearing rushed and under prepared, even forgetting to bring the correct supporting evidence to Court. Whilst instructing solicitors need to bear some responsibility for this, more work needs to be done by the experts giving evidence. Judgment in Pickering v Cambridge University Hospitals NHS Foundation Trust was handed down just last month and the case is a salutary tale for aspiring and current expert witnesses alike, a reminder of the need to:


In the evening of 24 September 2015, the Claimant, then 52, noticed that she had pins and needles in her foot. Of note, she suffered from a pre-existing heart condition (Atrial Fibrillation) that left her susceptible to blood clots. Her right foot became cold and white, which lasted for a few minutes before returning to normal, but then happened repeatedly. The Claimant attended A&E at Addenbrooke's Hospital where she was examined and discharged without anti-coagulation treatment - in this case Heparin. It was agreed by both parties – only after the Defendant’s A and E expert witness was had provided evidence - that the failure to provide Heparin was a breach of duty by the Trust.

She was sent to the out of hours GP, before being sent back to A&E and then home the next day. Over the next two days, the Claimant felt relatively normal and simply called her GP to ‘check in’, but on 27 September very sadly suffered a "massive stroke”.

The Court had to determine whether, but for the Defendant's negligence, the Claimant would not have suffered a stroke had she been treated with Heparin within the 48 hours in question. The medical literature does not offer definitive evidence in respect of treatment in an emergency setting of atrial fibrillation with a clot in the left atrium or LAA which has already fired off an embolus; obviously there is no ethical way of obtaining data for comparison purposes. As such, the ability of the experts to clearly explain their perspective on the issue in question was perhaps even more important than usual. The Claimant maintained that treatment with Heparin would have had a front loaded effect and avoided the stroke. The Defendant's expert, whilst accepting that Heparin was over 90% effective in preventing DVT and PE within 2-3 days of treatment, maintained his position that the efficacy of Heparin in those scenarios was not applicable in this case, and that the beneficial effect of Heparin would have only kicked in after 30 days. Notably, both experts accepted that Heparin prevents new clot growth and the propagation (growth) of existing clots. The rest of the article will focus on the performance of the key experts in this matter, and how that affected the Judgment.

The Experts

The evidence on breach

The Judge found the evidence of the Claimant’s expert witness consultant in A&E medicine, ‘persuasive, logical and clear’ that no reasonable A&E clinician would have let the Claimant leave without offering her advice on the "significant risk of further embolisation" and advising her that she needed Heparin "to reduce the risk of further embolic events".

By contrast, the Defendant's A&E consultant expert, demonstrated an inability to support his own opinion when under cross examination; his performance is a reminder to all expert witnesses of the need to be able to evidence assertions. Whilst he initially advised the Court that it was entirely reasonable not to treat the Claimant with Heparin because there was no evidence of ongoing leg ischaemia, during live cross examination he could not explain why it would be safe to make the Claimant wait for anti-coagulation when the Defendant's clinicians had Heparin in the fridge and a simple injection would start the protective process. Indeed, in the Judge’s words, “he came so close [to agreeing with the Claimant’s expert] as to be indicating to the Court that he was relenting.”

Following the evidence of the Defendant’s expert, the Defendant conceded both breach of duty and the fact that the Claimant would have taken the advice to start Heparin. It was then necessary to consider the issue of whether administering heparin at the time of the first appointment at A&E could have avoided the stroke suffered by the Claimant.


Four medical experts reported on causation. Taking the first pair, the Claimant instructed an eminent consultant neurologist, whilst the Defendant instructed a consultant in general medicine, geriatrics and strokes. It can always be a little challenging when the parties instruct experts in different fields, but they reached some agreement, stating in their joint report that:

The Defendant expert deferred to the haematologists but thought that anti-coagulant would not have saved the Claimant. The Claimant expert maintained that Heparin would have prevented the stroke and relied on a paper by Weitz et al published in 1997. Unfortunately, the Claimant’s expert was cross-examined on the content of this article, and it transpired that he had misquoted from it in the joint report. As such, he had to admit his error, confirming that he was summarising a different paper whose name he could not recall, and which he had not shown to either the Defendant’s expert or to the Court. Situations like this, although in this instance not fatal for the case, can create real problems and unnecessary stress for all those concerned and should be avoided.

Expert Haematology evidence

Turning to the key evidence, the Claimant’s haematology expert asked the question "Would Heparin have prevented the stroke?" He relied on the following points to support his argument that it would:

He also confirmed that Heparin is an effective anti-coagulant in the emergency setting which the Claimant was presented with on 24 September. By contrast, the Defendant’s expert argued:

"In my opinion Heparin would have been ineffective in preventing the Claimant's stroke, similar to the lack of effectiveness demonstrated in high risk AF patients in the two high quality phase three AF trials (where the mechanism of stroke and nature of embolising atrial thrombus would have been identical)."

He explained that with anti-coagulation the body's natural thrombolysis system results in "clot organisation and resolution" (his words) over time but advised that it takes three to four weeks for thrombi in the atrium to organise or resolve during the anti-coagulation treatment. He opined that the stroke potential still exists during those three to four weeks, despite anti-coagulation, probably because the pre-existing, fresh left atrial thrombus has not yet "organised or resolved". It appeared to the Judge that the Defendant’s expert was advising the Court that despite atrial clots reducing in size and resolving over 3-4 weeks of anti-coagulation, they do not become "organised" over that period so that their potential to fire off emboli remains the same as they decrease in size. The Judge “struggled to understand the logic of that in the face of the Defendant expert’s own struggled evidence that with anti-coagulation the body's natural thrombolysis system results in "clot organisation and resolution" (his words) over time”

In reaching his decision that he preferred the evidence of the Claimant’s haematology expert, the Judge took into account the fact that “[the Defendant’s expert] had a tendency to be rigid and then to produce rather extreme opinions”. To illustrate his viewpoint, the Judge pointed to the fact that the Defendant’s expert had asserted in cross examination that the scans in a paper he relied upon were unrepresentative “because the clinician who chose them may have been trying to prove his point”. The Judge claimed that “this assertion was unworthy of [the Defendant’s expert]”. The Judge was also unimpressed by the Defendant’s expert’s refusal “in his live evidence to descend into the detail as to why and how Heparin's great success in abolishing the risk of emboli from blood clots in DVT and PE should be occurring so quickly and why it is irrelevant to the atrial clots in this case.”

Overall, the Judge found that Heparin would have prevented new clot formation, prevented mother clot propagation (of the existing clot) and would have enabled the Claimant's body not only to reduce the size of the mother clot in the Claimant's LAA but also to make it less friable and more stable.


All expert witnesses should read the Judgment in full for this case¹ in order to understand the factors informing the Judge’s views - which in fact also included an implicit criticism of the Claimant expert haematologist for ‘lecturing’ from the witness box – and work hard to make sure that their opinions in the future are firmly based in logic, well tested and easily explainable. In Shakespeare’s words, ‘things done well and with a care, exempt themselves from fear; things done without example, in their issue. Are to be fear'd.' (Henry VIII Act 1, II).