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Medical device failure Expertise

by Dr Peter Rhys Lewis
BSc PhD FIMMM CEng MFSS
Forensic Engineer
(More about Dr Lewis)

Medical Equipment

Healthcare has improved greatly in the past two decades as a result of new technology and equipment. This, for example, includes incubators for premature babies and resuscitation equipment for heart attack victims, as well as that used for intensive care.

Such equipment often employs sophisticated electronic controls which can, like the hardware itself, fail and so precipitate a crisis. Failures can happen at the worst time, when staff are already fully occupied with caring for patients. Near misses are frequently reported by medical staff in the specialist literature, and junior staff such as nurses can report incidents anonymously to the Food and Drug Administration (FDA) in the US, and also now to the MHRA (Medical and Healthcare Products Regulatory Agency) in the UK. Such reported incidents should help equipment manufacturers to redesign failed components, issue warning notices or, in the very worst cases, recall and replace defective parts or entire devices which fail prematurely

Surgical aids

Catheters and sutures are examples of simple devices that help patients but where failure can imperil them. Catheters are simply tubes providing sustenance or drugs, and are often intravenous. However, they bypass the body’s normal defences to external threats such as bacteria and viruses. Should they fracture, then bacteria present on the tube have direct access to the body and can cause life-threatening infections. Air bubbles can also form and enter the body with possible fatal results.

New polymers have been introduced for catheters, but these may be sensitive to common hospital fluids such as cleaning agents used to reduce the infection problem. Environmental stress cracking and stress corrosion cracking are two problems manufacturers should test against when developing new products. But testing is not always done.

Much information is available in the literature. But even with the ready availability of the internet, careful literature searches have not always been performed by the designers. This can lead to avoidable failures in hospitals.

Sutures used to bind and stitch wounds after surgery can also fail suddenly, often with catastrophic consequences.

A common problem faced by investigators of alleged medical negligence is the loss of material evidence, often simply discarded by staff, or sometimes, discarded by manufacturers after examination. It makes subsequent investigations much more difficult, although failure modes can be inferred indirectly using other sources of information.

Orthopaedic aids

Crutches, walking sticks and frames help injured patients recover and are used widely by the elderly or infirm and in the post-operative setting. But these too can fail, often by fracturing at the weakest point in the design. This is usually at joints where imposed loads can be concentrated. And since it is the patient who applies that load, sudden fracture can cause further injury.

Analysis using microscopy of the fracture surfaces (or fractography) usually shows how the failure occurred. And other tools such as spectroscopy can show why brittle cracks developed. Examination of quality control records from the manufacturer can then isolate the cause of failure, and further failures can be reduced, if not eliminated. Since such devices must be light-weight for ease of use, they are usually made of light tough materials such as aluminium, composites or plastics.

Implants

Another set of medical devices that may be prone to premature failure are implants. Their failure offers a much higher risk of injury or worse to the patient.

Past failures that have occurred on a wide scale include breast implants and breast tissue expanders, as well as heart valves (such as one version of the Bjork-Shiley synthetic valve), synthetic hip joints and coronary balloon catheters and stents. These are all products that can be put under high stress when inserted into the body as well as when in position, so mechanical failure by fatigue, wear or overload is a distinct possibility if either the design is poor or manufacturing defects are present.

Device failures have often been detected first in the USA, probably because the US is the largest market for new products, This has resulted in tough regulations administered by the FDA. It has taken action in several cases, instigating criminal prosecutions, closing companies down and initiating recalls of faulty products. Their website is a first port of call for investigators examining product defects in new devices used outside the USA. And there is usually an extensive literature in the medical journals of failed products and incidents, easily accessible via web search engines.

Failure investigations usually involve both:

  • examination of specific failed products with a known history, and
  • traceability if it is found to be defective.

Many different methods are used to inspect failed products, including spectroscopy, microscopy and elemental analysis. Testing of new products under realistic conditions may also be employed to check product integrity.

by Dr Peter Rhys Lewis
BSc PhD FIMMM CEng MFSS
Forensic Engineer
(More about Dr Lewis)

 

 
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