Electromagnetic interference

EMI can affect several types of medical devices that have electrical or electronic systems. Examples of devices that can be affected include:

  • pacemakers or defibrillators – implanted or external
  • ECG monitors
  • infusion pumps.

We recommend that hospitals/trusts develop local policies to minimise the risk of interference with critical medical equipment.

Sources of EMI in hospitals and healthcare environments


There are many sources of EMI but the ones most likely to cause problems with certain medical devices include:
  • emergency vehicle/services radios
  • diathermy (electro-surgery)
  • mobile phones
  • radiofrequency identification (RFID) devices
  • electromagnets.

Emergency vehicle/services radios

These types of radios are used in emergency service vehicles including ambulances. Radio communications emit very strong electromagnetic waves and pose the highest risk of EMI with sensitive medical devices. They can have an effect at a distance of 5 metres. This means you should find out if sensitive equipment is used in the building close to parked ambulances.
  • Carry out a risk assessment before sensitive medical devices are used inside an ambulance and repeat if there are any changes to the vehicle radio system.
  • External pacemakers are especially susceptible to EMI – position the pacemaker as far as possible from the vehicle’s aerial(s). There should be a warning notice inside the ambulance to show the position of the aerial(s).
  • Ambulance, paramedic, cardiac and accident and emergency staff should be trained to recognise common interference events, and act appropriately.

Diathermy (electro-surgery)

This can affect active devices such as implanted pacemakers, cardioverter defibrillators and cochlear implants. Interference generated by monopolar surgical diathermy  is more severe than that generated by bipolar diathermy and can be sufficient to temporarily inhibit pacemaker output, give rise to a temporary increase in pacing, or cause a loss of programmed settings.

Mobile phones

The MHRA does not recommend a ban on the use of mobile phones in hospitals. However, a mobile phone can affect sensitive equipment if it is closer than one metre. Therefore we recommend that hospitals/trusts develop local policies to minimise the risk of interference in places such as:

  • treatment areas such as intensive therapy units (ITU), special care baby units (SCBU), operating theatres and accident and emergency departments
  • by the patient’s bedside when the patient is connected to any electro-medical device
  • other areas where interference with a device could have a detrimental effect on patients.

Radiofrequency identification systems

Radiofrequency identification (RFID) devices are used in healthcare establishments to trace and track equipment. They can also be used in a patient’s hospital bracelet.
RFIDs consist of two parts, a tag (which may be active or passive) and a detector (‘reader’). They are becoming more commonly used.
The level of interference from RFIDs is similar to that from mobile phones. They may cause problems with sensitive electronic medical devices such as pacemakers and monitors if they are closer than one metre.
Hospitals/trusts should do a risk assessment before using this technology and will need to decide on areas of restriction. The MHRA recommends caution:  avoid using these technologies in critical care areas such as intensive therapy units (ITU), special care baby units (SCBU) or where patients are attached to complex devices.
The risk of interference from RFIDs is influenced by the following:
  • type or power output of the reader
  • type or power rating of the tag (active tags only)
  • carrier frequency
  • distance between reader and medical device
  • location of use: in a store room there is a low or no risk; in an operating theatre the risk is higher.

 

Sources of EMI in other environments

Security body scanners

The MHRA is not aware of any interference problems between security body scanners (metal detectors) and sensitive medical devices such implanted pacemakers, implanted cardioverter defibrillators (ICDs) or neurostimulators.

People with these implants should walk through these scanners normally and not wait within the detection zone. As with mobile phones, keep a distance of 15 centimetres (6 inches) between a hand-held screening wand and the implanted device. Patients are reminded to carry their device registration card to show to staff when passing through security checks.

Recently introduced airport security body scanners use high frequency electromagnetic waves to scan a body. These electromagnetic waves pass through clothing and are reflected by the skin. They do not enter the body and so would not interfere with implanted electronic medical devices.

 

Non-EMI interference


The functions of active devices such as implanted pacemakers, cardioverter defibrillators and cochlear implants can be affected by fixed magnets, which can interfere by activating the magnetic reed-switches of the device. Small, fixed magnets are in a range of objects such as headphones, security tags on clothes in shops, and fastenings on mobile phone cases, clothes and jewellery. The effects can give rise to asynchronous mode pacing in pacemakers and inhibition of shock therapy in implantable defibrillators.

The risk is negligible as long as the item isn’t put too close to the implant (ie not closer than 3 cm). So for example, headphones should not be placed in the breast pocket of a shirt or jacket, or draped around the neck, even when not in use.

Enquiries
Email: dts@mhra.gsi.gov.uk or telephone 020 3080 6000


Page last modified: 07 November 2014