Kay's Tutor v Ayrshire and Arran Health Board

In a medically complex claim, causation must be established by acceptable evidence concerning the particular injury alleged. Evidence that an agent can cause some forms of neurological damage does not establish that it materially increases the risk of a distinct form, such as deafness.

The material-increase-in-risk principle cannot assist unless evidence first establishes that the defendant’s act was capable of increasing the risk of the injury in question. Scientific uncertainty about the precise mechanism does not supply that missing factual foundation. A court cannot establish causation by devising its own medical theory where the theory lacks evidential support and was not put to the expert witnesses.

A child suffering from pneumococcal meningitis received an admitted negligent intrathecal overdose of penicillin while being treated at hospital. The overdose caused convulsions, respiratory difficulties, unconsciousness and temporary hemiparesis. The child subsequently proved to have profound bilateral deafness, which was also a recognised consequence of pneumococcal meningitis.

The Lord Ordinary found that the overdose had contributed to the deafness and awarded £102,000. The First Division allowed the health board’s reclaiming motion. It held that the Lord Ordinary’s causal theory lacked medical evidence and reduced the award to £7,275, representing £3,000 with interest for the admitted effects of the overdose.

The child’s tutor appealed. The sole issue before the House was whether the overdose had caused or materially contributed to the deafness on the balance of probabilities.

1. Appeal dismissed unanimously. Lord Keith of Kinkel delivered the principal speech. Lord Griffiths, Lord Mackay of Clashfern and Lord Ackner reached the same conclusion upon the causation evidence. Lord Brandon of Oakbrook agreed with all the other speeches.

2. Per Lord Keith, the weight of the medical evidence established that the deafness resulted from pneumococcal meningitis and disclosed no causal connection with the penicillin overdose. Deafness was a common consequence of that disease. By contrast, the evidence contained no accepted instance of penicillin causing deafness. Lord Griffiths, Lord Mackay and Lord Ackner agreed that the appellant had failed to prove the necessary causal link.

3. Per Lord Keith and Lord Mackay, a finding that the child had good prospects of recovery before the overdose was not adequately supported by the evidence. It was based substantially upon an expert assessment affected by factual mistakes, including a mistake about the date of a cerebrospinal-fluid glucose measurement. In any event, favourable prospects of recovery would not themselves prove that the overdose materially contributed to the deafness.

4. Per Lord Griffiths and Lord Mackay, evidence that an intrathecal penicillin overdose could cause certain forms of neurological damage did not establish that it increased the risk of every form of neurological damage. The recorded overdose cases did not show damage causing deafness. It was therefore impermissible to treat fits, hemiparesis and deafness as interchangeable manifestations of a single risk.

5. McGhee v N.C.B. 1973 SC (HL) 37 did not assist. Per Lord Keith, that principle could have become relevant if acceptable medical evidence had shown that the overdose was known to increase the risk of meningitis causing deafness, even though science could not explain the precise mechanism. No such evidence existed. Lord Griffiths and Lord Mackay likewise held that the necessary factual foundation for reliance on that authority was absent.

6. The Lord Ordinary’s alternative theory—that the overdose weakened the body’s resistance to meningitis toxins—could not sustain the judgment. Per Lord Keith, Lord Griffiths and Lord Mackay, the theory had no tenable foundation in the medical evidence and had not been put to the experts. Lord Ackner agreed that determining complex medical causation upon an unsupported and untested theory was neither appropriate nor just.

1. House of Lords: The appeal was dismissed unanimously. The House upheld the conclusion that the overdose had not been proved to have caused or contributed to the deafness.

2. First Division of the Court of Session: On 18 December 1985 the court allowed the health board’s reclaiming motion, recalled the Lord Ordinary’s interlocutor and substituted damages of £3,000 with £4,275 interest for the admitted effects of the overdose.

3. Lord Ordinary: Lord Davidson held that the overdose contributed to the child’s deafness and awarded damages of £102,000.