Material contribution causation in clinical negligence

There have been two interesting recent judgments which have discussed the concept of material contribution causation in clinical negligence cases.

The first is Leach v North East Ambulance Service NHS Foundation Trust [2020] EWHC 2914 (QB) (30 October 2020). This concerned a claimant who had suffered a subarachnoid haemorrhage (SAH) as a result of a ruptured aneurysm, from which she had fortunately made a good recovery. However, she had also suffered significant post-traumatic stress disorder (PTSD), in particular in the form of severe anxiety. The defendant Trust had admitted breach of duty in respect of a 31-minute period of delay within a total time period of 109 minutes for the ambulance to arrive at the claimant’s house. What was in dispute was whether that delay had caused or materially contributed to the PTSD.

The defendant initially had asserted that the correct approach to causation was the “but for” test, namely that, if the claimant could not establish that her PTSD would not have developed “but for” the negligent period of delay, then the claim should fail. However, Freedman HHJ determined that the correct approach was as set out by Waller LJ in Bailey v The Ministry of Defence & Anor [2009] 1 WLR 1052 at p.1069 at [46]

“… I would summarise the position in relation to cumulative cause cases as follows. If the evidence demonstrates on a balance of probabilities that the injury would have occurred as a result of the non-tortious cause or causes in any event, the claimant will have failed to establish that the tortious cause contributed… If the evidence demonstrates that ‘but for’ the contribution of the tortious cause the injury would probably not have occurred, the claimant will (obviously) have discharged the burden. In a case where medical science cannot establish the probability that ‘but for’ an act of negligence the injury would not have happened but can establish that the contribution of the negligent cause was more than negligible, the ‘but for’ test is modified, and the claimant will succeed.”

The Judge summarised the causation principles to be applied to such cases [14] as follows:

“i)   If it can be shown that the claimant would have developed PTSD, in any event, irrespective of the negligent period of delay, then the claim fails;

ii) If it can be shown that but for the period of negligent delay the claimant would not have developed PTSD, then the claim succeeds;

iii)   If, on the other hand, the evidence is incapable of supporting either of the two propositions set out above, then if it can be shown that the negligent period of delay has made a material contribution to the PTSD, the claim succeeds”.

The defendant asserted that the claimant would have suffered PTSD anyway, irrespective of the negligent period of delay; the claimant claimed that it was not possible to know when the PTSD was triggered and the negligent period of delay had materially contributed to the PTSD. The Judge was critical of the defendant’s psychiatric expert, Dr Bowers, and preferred the evidence of the claimant’s expert, Dr Smith. He also referred to the reasoning of Globe J. in Ceri Leigh v London Ambulance NHS Trust [2014] EWHC 286 (QB), a case in which there had been an admitted 17-minute ambulance delay in a total of 50 minutes, also with subsequent PTSD, who stated that:

“There are innumerable variables in the circumstances that will give rise to the development of [PTSD] and in the people who are likely to suffer it. It is impossible to predict on any scientific or mathematical basis the moment after which someone will go on to suffer it”.

The Judge in Leach was neither persuaded by the defendant that, even on a balance of probabilities, at the point of onset of the SAH, it was likely the claimant would go on to develop PTSD nor at what point during the 109 minutes of waiting for an ambulance the PTSD likely developed; he considered that this was “pure speculation”. Equally, the period of 31-minutes of delay, which was a third of the overall period, was not of no importance. The Judge concluded that “It would be verging on the absurd… to suggest that that period of delay when the claimant was in acute distress, believing that the ambulance was not going to come, did not make a material contribution to the onset of her PTSD”. The Judge also noted that PTSD was an indivisible injury (i.e. not one in which the severity is dose or exposure related) and it was not possible to perform an apportionment exercise and, as such, the claimant was able to recover for the whole of the injury.

Contrast the second case of Davies v Frimley Health NHS Foundation Trust [2021] EWHC 169 (QB) (28 January 2021), a claim brought by the widower of the deceased who died from pneumococcal meningitis following an admitted negligent 2½-hour delay in administering intravenous antibiotics. Causation was again in dispute, it being asserted by the claimant that (a) had intravenous antibiotics been administered by 10:40 on the day of admission, it was likely, on the balance of probabilities, that the deceased would have survived; or (b) that the failure to do so made a material contribution to her death. The defendant disputed causation in full, including disputing that material contribution was relevant.

After a detailed analysis in the judgment of the expert evidence on both sides, Auerbach HHJ then discussed causation. He confirmed that what caused the claimant’s death was bacterial meningitis (i.e. medical causation) but that he had to decide whether, if the deceased had been given antibiotics before 10:40 (i.e. factual causation), was it more likely that she would have survived than died or more likely that she would have died than survived (i.e. legal causation). The Judge considered the recent case of Schembri v Marshall [2020] EWCA Civ 358, in which it was concluded that a claimant did not need to show the precise mechanism by which she would have survived with appropriate treatment and it was sufficient to look at the “bigger picture” to establish that she would have survived on a balance of probabilities. Following his detailed analysis of all the evidence, the Judge concluded that, had the antibiotics been administered on time, there was just enough time for them to reach the deceased’s brain ahead of the “tipping point” in the subsequent hour or so by when it would have been too late.

Although the Judge found for the claimant on traditional “but for” causation principles, he went on to discuss ‘material contribution’. He journeyed through the authorities and, in particular, cited Bailey and the same passage as had been cited in Leach (see above). The claimant had asserted the negligence made a material contribution to the disease process that led to death and this was a distinct legal doctrine. The defendant asserted that the authorities clearly established that the “but for” test can be modified by the application of a “material contribution” test but only in cases where (a) “but for” causation on the balance of probabilities cannot be determined, and (b) the injury is divisible, whereas in this case the injury (death) was indivisible.

The Judge concluded the following: (1) Where the harm is divisible, if the culpable conduct made a (material) contribution to the harm, the defendant will be liable to the extent of that contribution; (2) where the harm is indivisible, the defendant will be liable for the whole of the harm, if they caused it, applying “but for” principles; (3) if two wrongdoers have both together caused an indivisible injury, in respect of which it is impossible to apportion liability between them, then each is co-liable for the whole of the injury suffered; and, (4) in this case, the outcome of death was indivisible and material contribution did not have a part to play: the sole task of the Court was “to determine on the balance of probabilities whether, in a but for sense, the failure to start IV antibiotics by 10.40 on the day of admission caused her death or not” and the Judge did not think “any other legal doctrine could have been brought to bear in this case”.

It is perhaps difficult to reconcile the discussion and application of material contribution in the two judgments. In Leach, the judge appears to have been content to conclude that, if the claimant could not prove that, but for the negligent delay, she would not have PTSD (an indivisible injury), she could instead rely on proving that the negligent delay materially contributed to the PTSD. However, in Davies, the judge appears to have decided that, if the claimant could not prove that, but for the negligent delay, the deceased would not have died (also an indivisible injury), the claimant would not then be able to rely on proving that the negligent delay materially contributed to the death.

The judge in Davies considered material contribution was not a legal principle or exception to the “but for” test; if that is correct (which must be open to question given the higher authorities), it does, however, still appear to be an approach open to be taken dependent upon the available evidence (and bearing in mind the burden of proof), which was the approach in Leach. If the evidence is such that both the non-negligent and the negligent causes taken together result in injury, which on a balance of probabilities would not have occurred absent the negligence, straightforward “but for” causation can apply. If, however, it is not possible to apply “but for” principles on a balance of probabilities because of the absence of evidence, as in Leach (i.e. it was not possible to say that, absent the delay, on balance the claimant would not have suffered PTSD), yet the evidence is such that the negligent cause is nevertheless still a material factor in causing the injury, it would seem unjust for a claimant to be deemed not to have established causation of at least some injury. The extent of that injury would then either be the full extent, if it could not be apportioned between the contributing causes or, if it could be apportioned, the extent to which the negligent cause contributed. In such a situation, it is difficult to see how the “material contribution” test is not a modification of the “but for” test (even if it is not a legal doctrine per se), in that “but for” the delay, the injury would not have occurred at least not to the extent that it did in fact occur.

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