British Journal of Neurosurgery, June 2014; 28(3): 315–319 © 2014 The Neurosurgical Foundation ISSN: 0268-8697 print / ISSN 1360-046X online DOI: 10.3109/02688697.2014.896871
ORIGINAL ARTICLE
Medical negligence. An overview of legal theory and neurosurgical practice: causation Nicholas V. Todd
Br J Neurosurg Downloaded from informahealthcare.com by Kainan University on 04/11/15 For personal use only.
180 Portland Road, Sandyford, Newcastle upon Tyne, UK
The “but-for” test
Abstract This article discusses the principles of the law in relation to legal causation as applied to neurosurgical practice. Causation is a causal link between a breach of duty of care and the final harm. The fundamental “but-for” test for causation will be discussed, together with Chester v Afshar modified causation, prospective and retrospective probabilities of harm, loss of a chance, causation following breach of duty of care by omission, breaking the chain of causation, material contribution and the law in relation to multiple defendants, with neurosurgical examples.
The “but-for ” test is the basic principle that determines whether there is a causal link between the alleged breach of duty and the final harm. A breach of duty of care will be said to have caused harm if (i) harm would not have occurred if the breach of duty had not occurred and (ii) harm followed the identified breach of duty of care. If the same degree of harm would have occurred in any event (i.e. if the breach of duty had not occurred) then “but-for ” causation will not be demonstrated, the breach of duty did not cause the harm. Three nightwatchmen attended Accident and Emergency (A&E) with severe vomiting after drinking tea.3 The vessel in which they brewed the tea had been used to store arsenic. Dr Banarjee was contacted; his advice was to send the patients to their home and to contact their GPs. All three men died. The failure to admit the patients to hospital was found to be in breach of duty of care. Causation failed because the presumptive diagnosis would have been food poisoning, not arsenic poisoning; the deaths would not have been prevented by the usual treatment of food poisoning. It was more likely than not (in fact virtually certain) that the deaths would have occurred even if the breach of duty had not occurred, and hence causation was not established and the case failed. A premature baby became blind having been treated with excess oxygen (a well-known cause of blindness in premature babies).4 Excess oxygen was only one of five possible causes of blindness, the others being intraventricular haemorrhage, apnoea, hypercarbia and a patent ductus arteriosus. Treatment with excess oxygen was found to be in breach of duty of care but this was found only to be a possible cause of blindness, not the probable cause of blindness, hence the “but-for ” test was not satisfied, causation was not established and the case failed. A poor outcome will often have a number of causes, only one of which was caused by negligence. The contribution of the negligent cause needs to be over 50% if the claimant is to establish causation.
Keywords: causation; medical negligence; negligence; neurosurgery
Introduction Any claim in medical negligence requires a breach of duty of care, which is linked to causation. The claimant must establish that a legal requirement to act, or not, (duty of care) was breached and the breach caused harm (causation). There may be many potential causes of a patient’s final disability, not least that they had a medical condition requiring treatment. Only that part of a patient’s final disability that can be causally linked to the breach of duty will lead to recovery of damages.1 Causation is either established or it is not, that is, the test is all or nothing. If a claimant establishes causation they recover damages in full. If the likelihood of the link between the breach of duty and the harm caused is less than 50% then the assumption is that the harm was not linked to the breach of duty, the claimant fails entirely and receives no damages, not even a percentage of the damages. As an example, a class action looked for compensation for brain injuries that appeared to be linked to the use of pertussis vaccine.2 Despite evidence in the literature that use of the vaccine could cause brain injury in some patients, the Court found that the causal link was not more than 50% likely and the balance of probabilities test for causation was not satisfied, and therefore the claim failed.
Correspondence: Nicholas V. Todd, Consultant Neurosurgeon and Spinal Surgeon, 180 Portland Road, Newcastle upon Tyne, NE2 1DJ, UK. Tel: ⫹ 01912305927. Fax: ⫹ 0191-2302253. E-mail: [email protected] Received for publication 31 May 2013; accepted 16 February 2014
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Chester v Afshar modified causation A patient who fails the “but-for” test may, in rather particular circumstances, be able to demonstrate causation on the bases of patient autonomy and public policy.5 A patient with longstanding low back pain and leg pain had multi-level lumbar canal stenosis demonstrated on MR imaging. Lumbar laminectomies were recommended by the treating neurosurgeon. A surgical risk of cauda equina syndrome (CES) was not discussed with the patient. Unfortunately there was intraoperative damage to the cauda equina nerve roots. The case was considered by five law Lords who agreed that Mrs Chester would fail to demonstrate causation on the basis of the traditional “but-for” test. However, three of the five law Lords argued that patient autonomy in respect to consent is a fundamental right which should strongly be supported on the basis of public policy. Because the risk of CES was not explained the patient did not have the opportunity to consider that risk and therefore potentially she may not have had the operation that caused CES. The Court then, independently, found that, on a balance of probabilities, Mrs Chester would have deferred surgery and therefore CES would not have occurred. Those of us who have had the privilege of consenting large numbers of patients to neurosurgical procedures will understand that it is quite unusual for patients who have disabling symptoms that might potentially be helped by a surgical procedure to turn down the procedure because of low levels of a risk of complications. That of course is the classical “but-for” test which this patient would have failed. Two of the law Lords said that the case failed on causation, provided the patient would have had surgery at some point. They said that whenever the operation had been performed if the risks of CES were the same then the patient would have suffered CES at the time that she had undergone surgery (although CES would not have occurred on the specific occasion that it did). Therefore causation (for CES at some point) would not be established. I wonder, respectfully, if this is correct. In the unusual event of CES, that is a consequence of lumbar surgery, usually a cause is not identified. Where the cause is identified we can take a view as to whether, on a balance of probabilities, CES would have occurred if the operation had taken place on a different occasion. It seems to me that that is a much more difficult proposition where the cause of intraoperative CES is unknown. It may be that a number of different factors need to come together to cause intraoperative CES. It may be that in a particular case three different problems, an inadequate decompression, excessive retraction of the dura and a drop in the blood pressure, needed to come together at the same time to cause CES. If that is the case and if an operation had been carried out on a different occasion and perhaps by a different surgeon, it is improbable that all the factors that came together on the first occasion would come together on the second occasion and to the same extent, in which case causation should fail. Looking at this in another way, if the risk of intraoperative CES is 1 in 500 then whenever the operation was carried out there is over a 99.5% probability that intraoperative CES will not occur (although this statistical approach was rejected in this specific case5). Such a statistical approach will not apply
if the damage was caused by something that was entirely innate to the patient, that is, the damage would probably have occurred on any occasion. For example, massive unexpected intraoperative haemorrhage might occur in a patient with an unknown bleeding disorder. Assuming that the bleeding disorder would also not have been known if surgery had been carried out on a subsequent occasion, presumably a similar poor outcome would have occurred. The decision in Chester v Afshar5 emphasises the importance of patient autonomy in relation to consent and particularly consents to be at risks of surgery. It is generally felt that the decisions in Chester v Afshar are largely specific to the facts of this case.
Prospective and retrospective probabilities Determining “but-for” causation requires us to understand what the probability of the harm that in fact occurred would have been if the breach of duty of care had not occurred. The fact that the poor outcome occurred in a given case may mean that the probability of the poor outcome occurring in that individual would have been greater even if there had been no breach of duty. Using the case of Mrs Chester5 (discussed above): might it be that her risk of CES was greater than the usual risk because of something inherent to her anatomy/ pathophysiology, particularly given the fact that there was no suggestion that the operation was carried out to anything but an acceptable standard? This leads us into deep waters. If we accept a risk of CES in a patient undergoing lumbar laminectomy for multi-level stenosis of, say, 1 in 500 then that is the prospective risk. However, the risk of CES in that patient assessed retrospectively might be higher (because CES in fact occurred); perhaps the risk in that patient is 2%, 5%, 10% or more. If the retrospective risk is assessed at 5% this would be 25 times the prospective risk in the same patient. An increase in risk of 25 times is, comparatively, huge. Further discussion of these issues is beyond the intellect of this author but obviously these matters are crucially important to arguments about causation. When considering probabilities, it is worth noting that the statistical probability of a harmful event occurring in previously reported patients is not the same as the probability of cause and effect in a specific case.6 The particular facts of individual cases determine the cause and effect in each case.
Loss of a chance is no loss A negligent act, or omission, may increase the risk of harm and if the harm that occurred is more likely than not to have occurred in the absence of the breach (a greater than 50% chance), then the “but-for” test fails and subsequently the claim will also fail. Thus breach of duty of care is established and leads to loss of a chance of a better outcome (not a probability of a better outcome) but causation is not established and hence there is no loss. Compensation is for the damage that has (on balance) occurred and not for the loss of a chance of a better outcome. A 13-year-old boy fell, fracturing a neck of femur.7 The diagnosis was not made on a first visit to hospital which
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Medical negligence was found to be in breach of duty of care. The diagnosis was made, and the fracture was treated 5 days later, despite which he developed avascular necrosis of the femoral head causing a long-term disability. It was found that the probability of avascular necrosis occurring even with treatment on the first occasion was 75% and therefore, on a balance of probabilities (a probability of better than 50%) avascular necrosis would have occurred in any event, “but-for” causation was not established and hence the claim failed. Interestingly, two earlier Courts had awarded damages on the basis of 25% of the full damages, which represented the lost chance. The House of Lords confirmed that the “but-for” test for causation needed to be established on a balance of probabilities, better than 50%, and also confirmed that the “but-for” test was all or nothing. If “but-for” causation is not established the claim fails in its entirety. Looking at this the other way around, if the causation limb succeeds at, say, a 70% level damages are paid in full, not reduced by 30%. The principle that loss of a chance is no loss at all was reinforced in another case. A man had a non-Hodgkin’s lymphoma; the GP failed to refer him promptly for specialist care (found to be a breach of duty of care).8 The consequence was that the chance of survival was reduced from 42% to 25%. The claimant’s case was that although he could not prove that the GP’s breach caused harm at the 51% or better level, a principle established in another case (Fairchild1) that a breach that may have contributed to harm should allow him to recover damages in full. This was despite the fact that Fairchild was limited to its facts and was not approved for medical cases. A majority of law Lords rejected this loss of a chance claim confirming the standard test of a balance of probabilities which the patient clearly failed.
Breach of duty by omission Breach of duty of care can be a consequence of failing to do something that should have been done, breach of duty by omission. A 3-year old child with croup had three episodes of difficulty in breathing, in hospital. An anaesthetic SpR attended on the first two occasions and decided that intubation was not needed but did not attend on the third occasion; the child died.9 The failure to attend on the third occasion was found to be in breach of duty of care. The claimant had to demonstrate causation, that on a balance of probabilities, if the anaesthetic registrar had attended intubation would have followed and the death would have been prevented. “But-for” causation was applied as to whether the anaesthetic registrar would, probably, have intubated if she had attended on the third occasion. The Court, on the basis of logical analysis, found that she would probably have made the same decision, not to intubate, causation was therefore not established, the case failed. What might have happened absent a breach of duty of care might be actions or otherwise made by a doctor who was not the doctor whose omission was in breach of duty of care. A GP failed to refer a patient with bilateral radicular leg pain for urgent neurosurgical assessment; she was not referred prior to the development of CES which did not recover following treatment. The claimant had to demonstrate that earlier referral would have led to earlier decompressive surgery,
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preventing CES. A neurosurgical expert advised that based on the facts of the case, emergency decompressive surgery would not have been performed subsequently causation was not established and thus the case failed.10 Hypothetical causation was also the issue in the patient who underwent cardiac catheterisation.11 The brachial artery was catheterised, following the study the artery was closed with sutures. Unfortunately, the brachial artery was occluded by the sutures; this was found to be a recognised complication of this procedure, not in breach of duty of care. However, the patient was not warned to return if there was any evidence of vascular problems and that was a breach of duty of care. The occluded brachial artery was diagnosed 12 days after suturing and there was an attempt at vascular reconstruction. An aortogram was then performed, thrombus was dislodged into the basilar artery causing a locked-in syndrome following brainstem infarction. It was found that if the patient had been warned to return and if the arm had been re-explored within 48 h, angiography would never have been required and brainstem infarction would not have occurred. However, it was also found that if the patient had returned within 48 h, on a balance of probabilities, there would not have been an immediate re-operation, therefore, causation was not established and the case failed.
Breaking the chain of causation (novus actus interveniens) A new or intervening event (novus actus interveniens) may break the chain of causation such that the initial negligent act or omission may not be the cause of the final harm.12 A man suffered injury to the low back caused by breach of duty of care on the part of his employer. His earning capacity was reduced by 50%. He then developed an entirely unrelated spinal condition which completely prevented his ability to work. The new spinal condition was a novus actus; no damages were payable after the second (new) event occurred.12 This point is emphasised in two cases of attempted suicide. A psychiatric patient with a known risk of suicide was not observed properly (a negligent omission) and successfully committed suicide.13 Appropriate observations would have prevented suicide, the chain of causation was not broken, the claim succeeded. Another patient became depressed in hospital whilst being treated for physical problems, he jumped out of a window suffering further severe injuries.14 The treating doctors were not aware of the depressive illness nor any risk of suicide; jumping from the window was a novus actus which broke the chain of causation. The hospital treating the initial physical injuries was not liable for the injuries that were a consequence of the suicide attempt. It is unusual for the acts or omissions of doctors to break the chain of causation unless there is a high degree of negligence on the part of the doctors. A man injured his thumb at work which should have been treated to the extent that there would have been no long-term harm.15 Unfortunately, substandard treatment led to amputation of the thumb. Was the original injury, or the medical negligence, the cause of amputation of the thumb, i.e. did the medical negligence break the chain of causation? In this case medical negli-
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gence was found not to have broken the chain of causation; amputation of the thumb was a consequence of the injury that occurred at work. The logic of this, in part, is that it was the original accident that brought the patient to the care of his doctors, i.e. it was the original accident that put him in the position where the negligent act or omission could occur. Another man tripped at work injuring his leg.16 The injury was negligently treated and the leg had to be amputated. It was found that the negligent medical treatment did not break the chain of causation. If further injury (in this case amputation of the leg) is a foreseeable consequence of the primary injury, the primary injury will usually be seen to be the cause of the whole damage unless the treating doctors are found to be grossly negligent. It is likely that a very high degree of negligence, gross negligence or recklessness, on the part of treating doctors is necessary to break the chain of causation in cases where there has been a primary injury and then subsequent medical negligence causing harm.
Material contribution In many cases the final harm is caused by more than one mechanism. If only one of the mechanisms was a consequence of breach of duty it may not be possible to demonstrate that the harm caused by that breach of duty was more than 50% likely to have caused the harm, i.e. it may be impossible to satisfy the “but-for” test. However, it may be possible to demonstrate causation using a less strict test. If damage is caused by more than one mechanism and the relative contribution of each mechanism is unknown, causation can be established if one mechanism made a material contribution to the final damage.1,17,18 A patient underwent the endoscopic removal of common bile duct stones.19 Postoperative haemorrhage was negligently managed leaving the patient in what the Court found was a “weakened state”. She also developed pancreatitis (a non-negligent complication) which contributed to the “weakened state”. The patient was transferred initially to intensive care and then to a ward where she drank lemonade, vomited, aspirated and suffered a cardiac arrest and hypoxic brain damage. It was found that aspiration of vomit was a consequence of the “weakened state” for which there were two causes: negligent management of post-operative haemorrhage and non-negligent pancreatitis. The claimant could not prove that the negligent cause was more likely than not to have caused the “weakened state” but it was sufficient that it materially contributed to the “weakened state”. A material contribution is a contribution to the final harm that is more than negligible. Classical “but-for” causation is therefore modified: “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.”19 In another case a patient had a psychiatric disorder caused by several different factors, one of which was a negligent
failure to deal with stress at work.20 Although the case would have failed on the basis of classical “but-for” causation, it was found that stress at work materially contributed to the final psychiatric disorder and on that basis causation was accepted, the case succeeded.
Multiple defendants Different defendants could have contributed to harm. Each defendant is responsible in proportion to the risk of harm for which that defendant was responsible.21
Some neurosurgical considerations A patient was involved in a road traffic accident, a C5/6 fracture/dislocation was identified and treated. The patient had a long-term complete motor and sensory paraplegia. He sued the hospital for mismanagement of his condition, alleging that this caused the final harm. Evidence is crucial to determining causation in such cases. If it can be established, on a balance of probabilities, that there was complete motor and sensory paraplegia at the roadside then causation will not be established because we know that in the vast majority of such patients recovery motor or sensory function never happens. However, if there was good evidence that at the time of admission to A&E there was movement and/or sensation at/below the level of the lesion then the claimant will be able to say that the road traffic accident was not the cause of paraplegia and that secondary neurological deterioration following admission to hospital should have been preventable.22 If the claimant can demonstrate that there was a negligent failure to immobilise the cervical spine following admission to hospital, causation would succeed. In a similar fashion, a patient with a spinal epidural abscess might be admitted to hospital with complete motor and sensory paraplegia. This claimant would find it very difficult to establish causation regardless of the actions of the hospital doctors because even with best treatment very few patients recover neurological function where there is paraplegia that is a consequence of spinal infection. By contrast, if a patient with a spinal epidural abscess had walked into hospital with severe spinal pain only, if there was a negligent failure to diagnose and treat promptly, causation would probably be established because very few such patients would develop paraplegia if treated at a time they were walking. A patient had a decompressive lumbar laminectomy and developed a post-operative epidural haematoma (EDH). Neurological problems began to develop on the ward 2 h postoperatively, doctors were informed but failed to attend, which was found to be in breach of duty of care. The question now is what should have followed prompt assessment by the medical staff (factual causation) and with appropriate management, what would have been the long-term outcome (medical causation). Outcomes in patients with EDHs have recently been reviewed.23 This review demonstrated that good functional recovery is likely to be achieved if an EDH can be evacuated within 12 h of the onset of symptoms therefore if, on a balance of prob-
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Medical negligence abilities, diagnosis and treatment could, and should, have occurred within that 12-h period the claimant will establish causation, if not, on balance, he will not. Intra-operative injury to the spinal cord is a rare but wellrecognised complication of spinal surgery to which patients consent. If a patient wakes up with a new deficit caused by injury to the spinal cord the claimant may say that the operation was carried out to an unacceptably poor standard and that caused the cord injury. In such cases determining the cause of the cord injury is crucial. The two most useful things to study are the operation note and the post-operative imaging. The post-operative imaging may, for example, demonstrate that an interbody cage or disc replacement has been displaced posteriorly into the spinal canal, damaging the spinal cord. The operation note may record that an instrument or drill slipped into the spinal canal, damaging the spinal cord. Where we understand the cause of intraoperative cord injury we can decide whether such an injury was a consequence of breach of duty of care, or not. In other cases the MRI may demonstrate evidence of injury to the spinal cord but not the cause of that injury and the operation note may record a standard, uncomplicated, procedure. Under those circumstances it will be difficult for a claimant to say that the surgeon was in breach of duty of care because the claimant has to prove their case which is virtually impossible if they cannot clearly demonstrate the cause of the harm that has occurred.
Conclusion Legal causation is based upon a factual, causal connection between a breach of duty of care and the harm that occurred. This is embodied in the “but-for” test of causation which is the fundamental test of such a causal connection. As case law has been developed legal causation has, under specific circumstances, departed from the truly factual model, in the interests of justice. Declaration of interest: The author reports no declaration of interest. The author is responsible for the content and writing of the paper.
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References 1. Fairchild v Glenhaven Funeral Services Ltd [2002] UKHL 22. Available at: http://www.lexisnexis.com/uk/legal/ 2. Loveday v Renton [1990] 1 Med LR 117, CA 133. Available at: http:// www.lexisnexis.com/uk/legal/ 3. Barnett v. Chelsea and Kensington Hospital Management Committee, [1969] 1 QB 428 [1968] 1 All ER 1068. Available at: http://www.lexisnexis.com/uk/legal/ 4. Wilsher v Essex Area Health Authority 1988 AC 1074 [1988] 1 All ER 871. Available at: http://www.lexisnexis.com/uk/legal/ 5. Chester v. Afshar [2004] UKHL 41, [2005] 1 AC 134. Available at: http://www.lexisnexis.com/uk/legal/ 6. Meadow v GMC [2006] EWHC 146 (Admin), [2006] 2 All ER 329. Available at: http://www.lexisnexis.com/uk/legal/ 7. Hotson v East Berkshire Area Health Authority [1987] AC 750, [1987] 2 All ER 909. Available at: http://www.lexisnexis.com/uk/ legal/ 8. Gregg v Scott [2005] UKHL 2, [2005] 2 AC 176. Available at: http:// www.lexisnexis.com/uk/legal/ 9. Bolitho v. City and Hackney Health Authority [1998] AC 232, [1997] 4 All ER 771. Available at: http://www.lexisnexis.com/uk/legal/ 10. Zarb v Odetoyinbo [2006] EWHC 2880 (QB), 93 BMLR 166. Available at: http://www.lexisnexis.com/uk/legal/ 11. Joyce v Merton, Sutton and Wandsworth HA [1996] 7 Med LR 1, 27 BMLR 124. Available at: http://www.lexisnexis.com/uk/legal/ 12. Jobling v Associated Diaries Limited [1982] AC 794, [1981] 2 All ER 752. Available at: http://www.lexisnexis.com/uk/legal/ 13. Kirkham v. Chief Constable of the Greater Manchester Police [1990] 2 QB 283, [1990] 3 All ER 246. Available at: http://www. lexisnexis.com/uk/legal/ 14. Hyde v Tameside AHA [1981] 2 PN 26, [1981] CLY 1854. Available at: http://www.lexisnexis.com/uk/legal/ 15. Hogan v Bentinck West Hartley Collieries (Owners) Ltd [1949] 1 All ER 588, [1949] WN 109. Available at: http://www.lexisnexis.com/ uk/legal/ 16. Webb v Barclays Bank Plc and Portsmouth Hospitals NHS Trust [2001] EWCA Civ 1141, [2001] All ER (D) 202 (Jul). Available at: http://www.lexisnexis.com/uk/legal/ 17. McGhee v National Coal Board [1972] 3 All ER 1008, [1973] 1 WLR 1. Available at: http://www.lexisnexis.com/uk/legal/ 18. Bonnington Castings v Wardlaw [1956] AC 613, [1956] 1 All ER 615. Available at: http://www.lexisnexis.com/uk/legal/ 19. Bailey v Ministry of Defence [2008] EWCA Civ 883. Available at: http://www.lexisnexis.com/uk/legal/ 20. Dickins v O2 plc [2008] EWCA Civ 1144, [2009] IRLR 58. Available at: http://www.lexisnexis.com/uk/legal/ 21. Barker v Corus [2006] UKHL 20. Available at: http://www. lexisnexis.com/uk/legal/ 22. Poonnoose PM, Ravichandran G, McClelland MR. Missed and mismanaged injuries of the spinal cord. Trauma 2002;53:314–20. 23. Mukerji N, Todd N. Spinal epidural haematoma; factors influencing outcome. Br J Neurosurg 2013;27:712–7.
ORIGINAL ARTICLE
Medical negligence. An overview of legal theory and neurosurgical practice: causation Nicholas V. Todd
Br J Neurosurg Downloaded from informahealthcare.com by Kainan University on 04/11/15 For personal use only.
180 Portland Road, Sandyford, Newcastle upon Tyne, UK
The “but-for” test
Abstract This article discusses the principles of the law in relation to legal causation as applied to neurosurgical practice. Causation is a causal link between a breach of duty of care and the final harm. The fundamental “but-for” test for causation will be discussed, together with Chester v Afshar modified causation, prospective and retrospective probabilities of harm, loss of a chance, causation following breach of duty of care by omission, breaking the chain of causation, material contribution and the law in relation to multiple defendants, with neurosurgical examples.
The “but-for ” test is the basic principle that determines whether there is a causal link between the alleged breach of duty and the final harm. A breach of duty of care will be said to have caused harm if (i) harm would not have occurred if the breach of duty had not occurred and (ii) harm followed the identified breach of duty of care. If the same degree of harm would have occurred in any event (i.e. if the breach of duty had not occurred) then “but-for ” causation will not be demonstrated, the breach of duty did not cause the harm. Three nightwatchmen attended Accident and Emergency (A&E) with severe vomiting after drinking tea.3 The vessel in which they brewed the tea had been used to store arsenic. Dr Banarjee was contacted; his advice was to send the patients to their home and to contact their GPs. All three men died. The failure to admit the patients to hospital was found to be in breach of duty of care. Causation failed because the presumptive diagnosis would have been food poisoning, not arsenic poisoning; the deaths would not have been prevented by the usual treatment of food poisoning. It was more likely than not (in fact virtually certain) that the deaths would have occurred even if the breach of duty had not occurred, and hence causation was not established and the case failed. A premature baby became blind having been treated with excess oxygen (a well-known cause of blindness in premature babies).4 Excess oxygen was only one of five possible causes of blindness, the others being intraventricular haemorrhage, apnoea, hypercarbia and a patent ductus arteriosus. Treatment with excess oxygen was found to be in breach of duty of care but this was found only to be a possible cause of blindness, not the probable cause of blindness, hence the “but-for ” test was not satisfied, causation was not established and the case failed. A poor outcome will often have a number of causes, only one of which was caused by negligence. The contribution of the negligent cause needs to be over 50% if the claimant is to establish causation.
Keywords: causation; medical negligence; negligence; neurosurgery
Introduction Any claim in medical negligence requires a breach of duty of care, which is linked to causation. The claimant must establish that a legal requirement to act, or not, (duty of care) was breached and the breach caused harm (causation). There may be many potential causes of a patient’s final disability, not least that they had a medical condition requiring treatment. Only that part of a patient’s final disability that can be causally linked to the breach of duty will lead to recovery of damages.1 Causation is either established or it is not, that is, the test is all or nothing. If a claimant establishes causation they recover damages in full. If the likelihood of the link between the breach of duty and the harm caused is less than 50% then the assumption is that the harm was not linked to the breach of duty, the claimant fails entirely and receives no damages, not even a percentage of the damages. As an example, a class action looked for compensation for brain injuries that appeared to be linked to the use of pertussis vaccine.2 Despite evidence in the literature that use of the vaccine could cause brain injury in some patients, the Court found that the causal link was not more than 50% likely and the balance of probabilities test for causation was not satisfied, and therefore the claim failed.
Correspondence: Nicholas V. Todd, Consultant Neurosurgeon and Spinal Surgeon, 180 Portland Road, Newcastle upon Tyne, NE2 1DJ, UK. Tel: ⫹ 01912305927. Fax: ⫹ 0191-2302253. E-mail: [email protected] Received for publication 31 May 2013; accepted 16 February 2014
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Chester v Afshar modified causation A patient who fails the “but-for” test may, in rather particular circumstances, be able to demonstrate causation on the bases of patient autonomy and public policy.5 A patient with longstanding low back pain and leg pain had multi-level lumbar canal stenosis demonstrated on MR imaging. Lumbar laminectomies were recommended by the treating neurosurgeon. A surgical risk of cauda equina syndrome (CES) was not discussed with the patient. Unfortunately there was intraoperative damage to the cauda equina nerve roots. The case was considered by five law Lords who agreed that Mrs Chester would fail to demonstrate causation on the basis of the traditional “but-for” test. However, three of the five law Lords argued that patient autonomy in respect to consent is a fundamental right which should strongly be supported on the basis of public policy. Because the risk of CES was not explained the patient did not have the opportunity to consider that risk and therefore potentially she may not have had the operation that caused CES. The Court then, independently, found that, on a balance of probabilities, Mrs Chester would have deferred surgery and therefore CES would not have occurred. Those of us who have had the privilege of consenting large numbers of patients to neurosurgical procedures will understand that it is quite unusual for patients who have disabling symptoms that might potentially be helped by a surgical procedure to turn down the procedure because of low levels of a risk of complications. That of course is the classical “but-for” test which this patient would have failed. Two of the law Lords said that the case failed on causation, provided the patient would have had surgery at some point. They said that whenever the operation had been performed if the risks of CES were the same then the patient would have suffered CES at the time that she had undergone surgery (although CES would not have occurred on the specific occasion that it did). Therefore causation (for CES at some point) would not be established. I wonder, respectfully, if this is correct. In the unusual event of CES, that is a consequence of lumbar surgery, usually a cause is not identified. Where the cause is identified we can take a view as to whether, on a balance of probabilities, CES would have occurred if the operation had taken place on a different occasion. It seems to me that that is a much more difficult proposition where the cause of intraoperative CES is unknown. It may be that a number of different factors need to come together to cause intraoperative CES. It may be that in a particular case three different problems, an inadequate decompression, excessive retraction of the dura and a drop in the blood pressure, needed to come together at the same time to cause CES. If that is the case and if an operation had been carried out on a different occasion and perhaps by a different surgeon, it is improbable that all the factors that came together on the first occasion would come together on the second occasion and to the same extent, in which case causation should fail. Looking at this in another way, if the risk of intraoperative CES is 1 in 500 then whenever the operation was carried out there is over a 99.5% probability that intraoperative CES will not occur (although this statistical approach was rejected in this specific case5). Such a statistical approach will not apply
if the damage was caused by something that was entirely innate to the patient, that is, the damage would probably have occurred on any occasion. For example, massive unexpected intraoperative haemorrhage might occur in a patient with an unknown bleeding disorder. Assuming that the bleeding disorder would also not have been known if surgery had been carried out on a subsequent occasion, presumably a similar poor outcome would have occurred. The decision in Chester v Afshar5 emphasises the importance of patient autonomy in relation to consent and particularly consents to be at risks of surgery. It is generally felt that the decisions in Chester v Afshar are largely specific to the facts of this case.
Prospective and retrospective probabilities Determining “but-for” causation requires us to understand what the probability of the harm that in fact occurred would have been if the breach of duty of care had not occurred. The fact that the poor outcome occurred in a given case may mean that the probability of the poor outcome occurring in that individual would have been greater even if there had been no breach of duty. Using the case of Mrs Chester5 (discussed above): might it be that her risk of CES was greater than the usual risk because of something inherent to her anatomy/ pathophysiology, particularly given the fact that there was no suggestion that the operation was carried out to anything but an acceptable standard? This leads us into deep waters. If we accept a risk of CES in a patient undergoing lumbar laminectomy for multi-level stenosis of, say, 1 in 500 then that is the prospective risk. However, the risk of CES in that patient assessed retrospectively might be higher (because CES in fact occurred); perhaps the risk in that patient is 2%, 5%, 10% or more. If the retrospective risk is assessed at 5% this would be 25 times the prospective risk in the same patient. An increase in risk of 25 times is, comparatively, huge. Further discussion of these issues is beyond the intellect of this author but obviously these matters are crucially important to arguments about causation. When considering probabilities, it is worth noting that the statistical probability of a harmful event occurring in previously reported patients is not the same as the probability of cause and effect in a specific case.6 The particular facts of individual cases determine the cause and effect in each case.
Loss of a chance is no loss A negligent act, or omission, may increase the risk of harm and if the harm that occurred is more likely than not to have occurred in the absence of the breach (a greater than 50% chance), then the “but-for” test fails and subsequently the claim will also fail. Thus breach of duty of care is established and leads to loss of a chance of a better outcome (not a probability of a better outcome) but causation is not established and hence there is no loss. Compensation is for the damage that has (on balance) occurred and not for the loss of a chance of a better outcome. A 13-year-old boy fell, fracturing a neck of femur.7 The diagnosis was not made on a first visit to hospital which
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Medical negligence was found to be in breach of duty of care. The diagnosis was made, and the fracture was treated 5 days later, despite which he developed avascular necrosis of the femoral head causing a long-term disability. It was found that the probability of avascular necrosis occurring even with treatment on the first occasion was 75% and therefore, on a balance of probabilities (a probability of better than 50%) avascular necrosis would have occurred in any event, “but-for” causation was not established and hence the claim failed. Interestingly, two earlier Courts had awarded damages on the basis of 25% of the full damages, which represented the lost chance. The House of Lords confirmed that the “but-for” test for causation needed to be established on a balance of probabilities, better than 50%, and also confirmed that the “but-for” test was all or nothing. If “but-for” causation is not established the claim fails in its entirety. Looking at this the other way around, if the causation limb succeeds at, say, a 70% level damages are paid in full, not reduced by 30%. The principle that loss of a chance is no loss at all was reinforced in another case. A man had a non-Hodgkin’s lymphoma; the GP failed to refer him promptly for specialist care (found to be a breach of duty of care).8 The consequence was that the chance of survival was reduced from 42% to 25%. The claimant’s case was that although he could not prove that the GP’s breach caused harm at the 51% or better level, a principle established in another case (Fairchild1) that a breach that may have contributed to harm should allow him to recover damages in full. This was despite the fact that Fairchild was limited to its facts and was not approved for medical cases. A majority of law Lords rejected this loss of a chance claim confirming the standard test of a balance of probabilities which the patient clearly failed.
Breach of duty by omission Breach of duty of care can be a consequence of failing to do something that should have been done, breach of duty by omission. A 3-year old child with croup had three episodes of difficulty in breathing, in hospital. An anaesthetic SpR attended on the first two occasions and decided that intubation was not needed but did not attend on the third occasion; the child died.9 The failure to attend on the third occasion was found to be in breach of duty of care. The claimant had to demonstrate causation, that on a balance of probabilities, if the anaesthetic registrar had attended intubation would have followed and the death would have been prevented. “But-for” causation was applied as to whether the anaesthetic registrar would, probably, have intubated if she had attended on the third occasion. The Court, on the basis of logical analysis, found that she would probably have made the same decision, not to intubate, causation was therefore not established, the case failed. What might have happened absent a breach of duty of care might be actions or otherwise made by a doctor who was not the doctor whose omission was in breach of duty of care. A GP failed to refer a patient with bilateral radicular leg pain for urgent neurosurgical assessment; she was not referred prior to the development of CES which did not recover following treatment. The claimant had to demonstrate that earlier referral would have led to earlier decompressive surgery,
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preventing CES. A neurosurgical expert advised that based on the facts of the case, emergency decompressive surgery would not have been performed subsequently causation was not established and thus the case failed.10 Hypothetical causation was also the issue in the patient who underwent cardiac catheterisation.11 The brachial artery was catheterised, following the study the artery was closed with sutures. Unfortunately, the brachial artery was occluded by the sutures; this was found to be a recognised complication of this procedure, not in breach of duty of care. However, the patient was not warned to return if there was any evidence of vascular problems and that was a breach of duty of care. The occluded brachial artery was diagnosed 12 days after suturing and there was an attempt at vascular reconstruction. An aortogram was then performed, thrombus was dislodged into the basilar artery causing a locked-in syndrome following brainstem infarction. It was found that if the patient had been warned to return and if the arm had been re-explored within 48 h, angiography would never have been required and brainstem infarction would not have occurred. However, it was also found that if the patient had returned within 48 h, on a balance of probabilities, there would not have been an immediate re-operation, therefore, causation was not established and the case failed.
Breaking the chain of causation (novus actus interveniens) A new or intervening event (novus actus interveniens) may break the chain of causation such that the initial negligent act or omission may not be the cause of the final harm.12 A man suffered injury to the low back caused by breach of duty of care on the part of his employer. His earning capacity was reduced by 50%. He then developed an entirely unrelated spinal condition which completely prevented his ability to work. The new spinal condition was a novus actus; no damages were payable after the second (new) event occurred.12 This point is emphasised in two cases of attempted suicide. A psychiatric patient with a known risk of suicide was not observed properly (a negligent omission) and successfully committed suicide.13 Appropriate observations would have prevented suicide, the chain of causation was not broken, the claim succeeded. Another patient became depressed in hospital whilst being treated for physical problems, he jumped out of a window suffering further severe injuries.14 The treating doctors were not aware of the depressive illness nor any risk of suicide; jumping from the window was a novus actus which broke the chain of causation. The hospital treating the initial physical injuries was not liable for the injuries that were a consequence of the suicide attempt. It is unusual for the acts or omissions of doctors to break the chain of causation unless there is a high degree of negligence on the part of the doctors. A man injured his thumb at work which should have been treated to the extent that there would have been no long-term harm.15 Unfortunately, substandard treatment led to amputation of the thumb. Was the original injury, or the medical negligence, the cause of amputation of the thumb, i.e. did the medical negligence break the chain of causation? In this case medical negli-
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gence was found not to have broken the chain of causation; amputation of the thumb was a consequence of the injury that occurred at work. The logic of this, in part, is that it was the original accident that brought the patient to the care of his doctors, i.e. it was the original accident that put him in the position where the negligent act or omission could occur. Another man tripped at work injuring his leg.16 The injury was negligently treated and the leg had to be amputated. It was found that the negligent medical treatment did not break the chain of causation. If further injury (in this case amputation of the leg) is a foreseeable consequence of the primary injury, the primary injury will usually be seen to be the cause of the whole damage unless the treating doctors are found to be grossly negligent. It is likely that a very high degree of negligence, gross negligence or recklessness, on the part of treating doctors is necessary to break the chain of causation in cases where there has been a primary injury and then subsequent medical negligence causing harm.
Material contribution In many cases the final harm is caused by more than one mechanism. If only one of the mechanisms was a consequence of breach of duty it may not be possible to demonstrate that the harm caused by that breach of duty was more than 50% likely to have caused the harm, i.e. it may be impossible to satisfy the “but-for” test. However, it may be possible to demonstrate causation using a less strict test. If damage is caused by more than one mechanism and the relative contribution of each mechanism is unknown, causation can be established if one mechanism made a material contribution to the final damage.1,17,18 A patient underwent the endoscopic removal of common bile duct stones.19 Postoperative haemorrhage was negligently managed leaving the patient in what the Court found was a “weakened state”. She also developed pancreatitis (a non-negligent complication) which contributed to the “weakened state”. The patient was transferred initially to intensive care and then to a ward where she drank lemonade, vomited, aspirated and suffered a cardiac arrest and hypoxic brain damage. It was found that aspiration of vomit was a consequence of the “weakened state” for which there were two causes: negligent management of post-operative haemorrhage and non-negligent pancreatitis. The claimant could not prove that the negligent cause was more likely than not to have caused the “weakened state” but it was sufficient that it materially contributed to the “weakened state”. A material contribution is a contribution to the final harm that is more than negligible. Classical “but-for” causation is therefore modified: “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.”19 In another case a patient had a psychiatric disorder caused by several different factors, one of which was a negligent
failure to deal with stress at work.20 Although the case would have failed on the basis of classical “but-for” causation, it was found that stress at work materially contributed to the final psychiatric disorder and on that basis causation was accepted, the case succeeded.
Multiple defendants Different defendants could have contributed to harm. Each defendant is responsible in proportion to the risk of harm for which that defendant was responsible.21
Some neurosurgical considerations A patient was involved in a road traffic accident, a C5/6 fracture/dislocation was identified and treated. The patient had a long-term complete motor and sensory paraplegia. He sued the hospital for mismanagement of his condition, alleging that this caused the final harm. Evidence is crucial to determining causation in such cases. If it can be established, on a balance of probabilities, that there was complete motor and sensory paraplegia at the roadside then causation will not be established because we know that in the vast majority of such patients recovery motor or sensory function never happens. However, if there was good evidence that at the time of admission to A&E there was movement and/or sensation at/below the level of the lesion then the claimant will be able to say that the road traffic accident was not the cause of paraplegia and that secondary neurological deterioration following admission to hospital should have been preventable.22 If the claimant can demonstrate that there was a negligent failure to immobilise the cervical spine following admission to hospital, causation would succeed. In a similar fashion, a patient with a spinal epidural abscess might be admitted to hospital with complete motor and sensory paraplegia. This claimant would find it very difficult to establish causation regardless of the actions of the hospital doctors because even with best treatment very few patients recover neurological function where there is paraplegia that is a consequence of spinal infection. By contrast, if a patient with a spinal epidural abscess had walked into hospital with severe spinal pain only, if there was a negligent failure to diagnose and treat promptly, causation would probably be established because very few such patients would develop paraplegia if treated at a time they were walking. A patient had a decompressive lumbar laminectomy and developed a post-operative epidural haematoma (EDH). Neurological problems began to develop on the ward 2 h postoperatively, doctors were informed but failed to attend, which was found to be in breach of duty of care. The question now is what should have followed prompt assessment by the medical staff (factual causation) and with appropriate management, what would have been the long-term outcome (medical causation). Outcomes in patients with EDHs have recently been reviewed.23 This review demonstrated that good functional recovery is likely to be achieved if an EDH can be evacuated within 12 h of the onset of symptoms therefore if, on a balance of prob-
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Medical negligence abilities, diagnosis and treatment could, and should, have occurred within that 12-h period the claimant will establish causation, if not, on balance, he will not. Intra-operative injury to the spinal cord is a rare but wellrecognised complication of spinal surgery to which patients consent. If a patient wakes up with a new deficit caused by injury to the spinal cord the claimant may say that the operation was carried out to an unacceptably poor standard and that caused the cord injury. In such cases determining the cause of the cord injury is crucial. The two most useful things to study are the operation note and the post-operative imaging. The post-operative imaging may, for example, demonstrate that an interbody cage or disc replacement has been displaced posteriorly into the spinal canal, damaging the spinal cord. The operation note may record that an instrument or drill slipped into the spinal canal, damaging the spinal cord. Where we understand the cause of intraoperative cord injury we can decide whether such an injury was a consequence of breach of duty of care, or not. In other cases the MRI may demonstrate evidence of injury to the spinal cord but not the cause of that injury and the operation note may record a standard, uncomplicated, procedure. Under those circumstances it will be difficult for a claimant to say that the surgeon was in breach of duty of care because the claimant has to prove their case which is virtually impossible if they cannot clearly demonstrate the cause of the harm that has occurred.
Conclusion Legal causation is based upon a factual, causal connection between a breach of duty of care and the harm that occurred. This is embodied in the “but-for” test of causation which is the fundamental test of such a causal connection. As case law has been developed legal causation has, under specific circumstances, departed from the truly factual model, in the interests of justice. Declaration of interest: The author reports no declaration of interest. The author is responsible for the content and writing of the paper.
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References 1. Fairchild v Glenhaven Funeral Services Ltd [2002] UKHL 22. Available at: http://www.lexisnexis.com/uk/legal/ 2. Loveday v Renton [1990] 1 Med LR 117, CA 133. Available at: http:// www.lexisnexis.com/uk/legal/ 3. Barnett v. Chelsea and Kensington Hospital Management Committee, [1969] 1 QB 428 [1968] 1 All ER 1068. Available at: http://www.lexisnexis.com/uk/legal/ 4. Wilsher v Essex Area Health Authority 1988 AC 1074 [1988] 1 All ER 871. Available at: http://www.lexisnexis.com/uk/legal/ 5. Chester v. Afshar [2004] UKHL 41, [2005] 1 AC 134. Available at: http://www.lexisnexis.com/uk/legal/ 6. Meadow v GMC [2006] EWHC 146 (Admin), [2006] 2 All ER 329. Available at: http://www.lexisnexis.com/uk/legal/ 7. Hotson v East Berkshire Area Health Authority [1987] AC 750, [1987] 2 All ER 909. Available at: http://www.lexisnexis.com/uk/ legal/ 8. Gregg v Scott [2005] UKHL 2, [2005] 2 AC 176. Available at: http:// www.lexisnexis.com/uk/legal/ 9. Bolitho v. City and Hackney Health Authority [1998] AC 232, [1997] 4 All ER 771. Available at: http://www.lexisnexis.com/uk/legal/ 10. Zarb v Odetoyinbo [2006] EWHC 2880 (QB), 93 BMLR 166. Available at: http://www.lexisnexis.com/uk/legal/ 11. Joyce v Merton, Sutton and Wandsworth HA [1996] 7 Med LR 1, 27 BMLR 124. Available at: http://www.lexisnexis.com/uk/legal/ 12. Jobling v Associated Diaries Limited [1982] AC 794, [1981] 2 All ER 752. Available at: http://www.lexisnexis.com/uk/legal/ 13. Kirkham v. Chief Constable of the Greater Manchester Police [1990] 2 QB 283, [1990] 3 All ER 246. Available at: http://www. lexisnexis.com/uk/legal/ 14. Hyde v Tameside AHA [1981] 2 PN 26, [1981] CLY 1854. Available at: http://www.lexisnexis.com/uk/legal/ 15. Hogan v Bentinck West Hartley Collieries (Owners) Ltd [1949] 1 All ER 588, [1949] WN 109. Available at: http://www.lexisnexis.com/ uk/legal/ 16. Webb v Barclays Bank Plc and Portsmouth Hospitals NHS Trust [2001] EWCA Civ 1141, [2001] All ER (D) 202 (Jul). Available at: http://www.lexisnexis.com/uk/legal/ 17. McGhee v National Coal Board [1972] 3 All ER 1008, [1973] 1 WLR 1. Available at: http://www.lexisnexis.com/uk/legal/ 18. Bonnington Castings v Wardlaw [1956] AC 613, [1956] 1 All ER 615. Available at: http://www.lexisnexis.com/uk/legal/ 19. Bailey v Ministry of Defence [2008] EWCA Civ 883. Available at: http://www.lexisnexis.com/uk/legal/ 20. Dickins v O2 plc [2008] EWCA Civ 1144, [2009] IRLR 58. Available at: http://www.lexisnexis.com/uk/legal/ 21. Barker v Corus [2006] UKHL 20. Available at: http://www. lexisnexis.com/uk/legal/ 22. Poonnoose PM, Ravichandran G, McClelland MR. Missed and mismanaged injuries of the spinal cord. Trauma 2002;53:314–20. 23. Mukerji N, Todd N. Spinal epidural haematoma; factors influencing outcome. Br J Neurosurg 2013;27:712–7.
