Breach of duty and causation in medical negligence: a complete guide

Medical negligence cases require both breach of duty and causation to be established independently. The distinction is fundamental and is the reason some apparently strong cases fail and some apparently weaker cases succeed. This article sets out how I address both issues when I am instructed on a negligence case.

Medical negligence cases in Ireland (and other common-law jurisdictions) require the claimant to establish two separate issues: breach of duty and causation. Each is independently necessary. A finding of one without the other is not sufficient to support a claim. Understanding the distinction is central to running these cases effectively, instructing the right experts, and managing realistic expectations on all sides.

This guide walks through what each of these concepts means, how they are established in practice, and how the medical evidence addresses each. It also covers some of the nuances and complications that arise in real cases.

Breach of duty asks whether the care provided fell below the standard that could reasonably be expected of a competent practitioner in the relevant field. The standard is not perfection. Doctors are not held to a standard of guaranteed success. They are held to a standard of competent practice. The standard is what a reasonable body of professional opinion would have done in the same circumstances.

The Irish legal framework for assessing breach of duty draws on the Bolam test from English law, modified in Ireland by the Supreme Court’s decision in Dunne v National Maternity Hospital (1989) and subsequent cases. The principle is that a doctor is not negligent if the practice they followed is supported by a substantial body of professional opinion, even if other doctors might have acted differently. The Bolitho qualification, which the Irish courts have followed in principle, adds the requirement that the body of opinion must withstand logical analysis. A practice that is supported by some doctors but which cannot be rationally defended will not protect a defendant.

In practical terms, breach of duty asks: did the clinician do something that no competent practitioner in that situation would have done, or fail to do something that a competent practitioner would have done? The standard is set at the time of the alleged negligence, not with the benefit of hindsight. What seems obvious in retrospect may not have been obvious at the time, and the assessment must consider what was known and reasonable when the decisions were made.

The medical expert’s role in addressing breach of duty involves several elements. The expert reviews all the relevant records, including hospital records, GP records, investigations, and any other documentation. The expert identifies the standard of care that applied at the time. This may be drawn from clinical guidelines, professional consensus, peer-reviewed literature, and the expert’s own knowledge of practice in the relevant specialty. The expert then assesses whether the care given met that standard. Where it did not, the expert identifies the specific shortfall.

Causation asks whether the breach (if established) caused the harm complained of. This is the question of whether things would have been different if the breach had not occurred. It is sometimes called the ‘but for’ test: but for the breach, would the harm have occurred?

Causation can be straightforward or complex depending on the case. In some cases, the link between breach and harm is obvious. A failure to diagnose a fracture leads to delayed treatment and an obvious worsening of the outcome. A medication error leading to a specific complication has a clear causal link. In other cases, the link is less clear. A diagnosis missed at an early stage may or may not have led to a different outcome even if it had been made promptly. The relevant question is the balance of probabilities: was it more likely than not that timely action would have produced a better outcome?

Causation is often the harder issue to establish in medical negligence cases. Many conditions have a natural history that cannot be entirely reversed even by optimal treatment. Some have outcomes that depend more on the underlying disease than on the timing or quality of treatment. Distinguishing what would have happened with appropriate care from what actually happened requires careful clinical reasoning supported by the available evidence.

The medical expert addressing causation considers several questions. What was the natural history of the underlying condition? What would have been the realistic outcome with appropriate care? How does the actual outcome compare? What is the most likely explanation for the difference? Where the answer is uncertain, what is the balance of probabilities?

An example may help. Consider a patient with sepsis who is seen in an emergency department and discharged. The patient returns a day later, more unwell, and is admitted. The patient ultimately survives but with significant complications. Was there a breach of duty? Possibly yes, if the first assessment failed to recognise warning signs that a reasonable practitioner would have recognised. Was there causation? This is the harder question. If the patient would have had the same outcome even with admission at the first visit (because the disease was already established and the complications were unavoidable), then there is no causation. If the patient would have done substantially better with earlier treatment, then there is causation. Establishing this requires careful assessment of the timing, the underlying condition, the natural history, and the evidence base for the effects of timely treatment.

The concept of material contribution sometimes simplifies the causation analysis. Where multiple factors contribute to an outcome and it cannot be said with certainty which factor was decisive, the law may accept that the breach made a material contribution to the harm. This is particularly relevant in cases involving multiple potential causes (such as industrial disease cases) but can also apply in some medical contexts.

Loss of chance is a related but legally distinct concept. The argument is that even when full causation cannot be established (because the outcome might not have been better even with non-negligent care), the patient has lost a chance of a better outcome and is entitled to compensation for that lost chance. The legal treatment of loss of chance varies between jurisdictions and is unsettled in Ireland. The English courts have generally declined to accept loss of chance as a basis for compensation in medical negligence (in the Gregg v Scott case), although the position is more nuanced in other contexts.

For medical negligence experts, the report must address breach of duty and causation as separate issues. The reasoning for each should be set out clearly. Where one is established but the other is not, this should be stated openly. Where the evidence is uncertain on either issue, this should be acknowledged honestly. The expert who tries to extend an opinion beyond what the evidence supports loses credibility.

The structure of a medical negligence report typically separates the two issues clearly. After the factual chronology and clinical analysis, the report addresses breach: what was the standard of care, was it met, what specifically was the shortfall. The report then addresses causation: what would have happened with appropriate care, what actually happened, what is the link.

The expert who can opine on both issues within their genuine expertise is the right expert for the case. Where breach and causation involve different areas of expertise (for example, a breach by an emergency physician with consequences in a specialty area), multiple experts may be needed. The instructing solicitor needs to consider this at the start of the case.

For solicitors, the practical implications are several. The case strategy must consider both issues from the outset. A case with apparent breach but doubtful causation has a fundamental weakness that needs to be addressed through expert evidence or through realistic case management. Conversely, a case with strong causation but doubtful breach has a different problem, since the bad outcome is real but the legal foundation for compensation is weak.

For patients considering a medical negligence claim, the practical message is that even where the care provided was substandard, a claim may not succeed if causation cannot be established. The two questions are independent. Both need to be answerable in the affirmative for a claim to succeed. The medical expert’s role is to give an honest assessment of both, which sometimes supports the claim and sometimes does not.

For defendants and insurers, the medical evidence is similarly central. An independent assessment of breach and causation supports realistic case strategy, informs settlement discussions, and identifies the genuine strengths and weaknesses of the defence.

If you require an independent consultant medical report on this issue, I accept instructions from solicitors and insurers across Ireland. Reports are typically delivered within four weeks of instruction, with shorter turnaround available where required. Contact the practice through medical-legal.ie to discuss the case and confirm fees in advance.