Clinical negligence & novus actus interveniens

06 May 2019

Where the negligent act of A sets the scene for the negligent act of B, who transforms the outcome of A’s conduct into something of far greater consequence, is A responsible for the loss associated with B’s conduct?

In practical terms, negligent party A (the original tortfeasor) is liable for the outcome of negligent party B’s conduct, because such conduct is a foreseeable consequence of A’s negligence. However, the damage for which A is liable in negligence may be limited if the injury sustained was not reasonably foreseeable, or because the chain of causation is broken by a novus actus interveniens.

Novus actus interveniens is an independent, intervening act which breaks the chain of causation between a negligent act and the ultimate harm. A successful break in the chain of causation absolves the original tortfeasor from liability for the injured party’s ultimate loss.1 This inquiry is also known as the “scope of liability” which is reflected in section 5C(1)(b) of the Civil Liability Act 2002 (WA). This inquiry requires the Court to consider whether it is appropriate for the scope of the original tortfeasor’s liability to extend to the harm in question and whether liability for the harm should be imposed on the original tortfeasor.

Subsequent medical treatment must be “grossly negligent” to fall outside the scope of the original tortfeasor’s liability

Australian Courts have consistently held that to establish a novus actus interveniens capable of severing the chain of causation, the original tortfeasor must establish, on the balance of probabilities, that the subsequent treatment was “grossly negligent”, and therefore not a reasonably foreseeable consequence of the original injury. A mere error or lapse of judgment will not possess enough “causal potency” to amount to an intervening act capable of breaking the chain of causation.

Australian authorities suggest that medical treatment which is unforeseeable is treatment that is “inexcusably bad”, “completely outside the bounds of what any other reputable medical practitioner might prescribe”, or “so obviously unnecessary or improper that it is in the nature of a gratuitous aggravation of the injury” or “extravagant from the point of view of medical practice or routine.”

For example, in the case of Aquilina v NSW Insurance Ministerial Corporation (1994) 157, the negligent driver in a motor vehicle accident was held liable for both the back injuries sustained in the motor vehicle accident and the severe complications of negligently-performed back surgery (including brain damage). This was on the basis that the surgeon’s negligence did not amount to gross negligence and the back injuries from the motor vehicle accident carried the risk that some negligent medical treatment might be given.

Similarly, in the case of Liston v Liston (1981) 31 SASR 245, the South Australian Supreme Court held a negligent driver liable for the back injuries sustained in the car accident and a subsequent permanent back disability sustained as a result of an unsuccessful laminectomy. This was on the basis that there was nothing “ultroneous” nor “unreasonable or extraneous or extrinsic” about the surgeon’s decision to perform the laminectomy.

These cases reflect the widely held view that the original tortiously inflicted injury carries a foreseeable risk of being exacerbated by subsequent negligent medical treatment, and such treatment will not constitute a novus actus interveniens.

There is scarce case law dealing with intervening acts in the setting of clinical negligence. The vast majority of cases have arisen in the context of workers’ compensation, motor vehicle accident or occupier’s liability claims where the injured person seeks out treatment for a tortiously-inflicted injury that is carried out negligently, resulting in further injury.

In the absence of local authority, the English Court of Appeal decision of Wright v Cambridge Medical Group [2012] 3 WLR, offers helpful insight into the approach taken by the Court with respect to novus actus interveniens arguments in a clinical negligence context.

In that case, an infant developed a bacterial infection following discharge from hospital (for the treatment of chicken pox), causing the development of osteomyelitis in her hip bone. Three days after discharge from hospital, the infant’s mother telephoned a GP for medical advice however the GP did not review the infant, nor did the GP refer the infant for a review. The infant’s condition deteriorated over the ensuing days and she was referred to another hospital where she received inadequate and further delayed treatment, resulting in permanent injury to her hip.

The infant commenced an action against the GP clinic (by her next friend) alleging negligence for the late hospital referral, however the hospital was not named as a Defendant to these proceedings.

The GP clinic conceded that their practitioner was negligent in failing to review the infant (and that had the practitioner seen her, a hospital referral would or should have been made) but denied liability for the infant’s permanent hip injury on the basis that there was no causal link between this failure and the Plaintiff’s permanent injury.

By 3:2 majority, the Court of Appeal rejected the GP clinic’s argument that the hospital’s failure to render proper treatment was an intervening act that broke the chain of causation because “it was not such an egregious event in terms of degree or unusualness of the negligence or the period of time during which it lasted, to defeat or to destroy the causative link” between the GP clinic’s negligence and infant’s ultimate injury.

The Court of Appeal ultimately held that the late referral and inadequate hospital treatment were each causative of the infant’s injury, and therefore, there was an established link between the GP clinic’s negligence and her damage.

Moving forward

Issues involving intervening acts are typically complex, particularly in a clinical negligence context, and each case turns on the facts. Whilst the relevant case authorities offer limited assistance to differentiate gross medical negligence from ordinary actionable medical negligence, it is clear that the Courts set a very high bar in this regard.

The comments made by the majority in Wright reflect the standing position adopted in Australian decisions, namely, that in order to successfully establish a novus actus interveniens, the original tortfeasor must prove that the subsequent negligent treatment went beyond the realms of a “failure to take reasonable care”, and must instead, be considered outstandingly bad to amount to gross negligence, capable of breaking the chain of causation.

This article was written by Sarah Harrison, Partner and Lauren Aspley, Associate.

Sarah Harrison

P: +61 8 9420 1568


1 Mahoney v J Kruschich (Demolitions) Pty Ltd (1985) 156 CLR 522

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