Conductive Mattresses and Diathermy
Hazard [Health Devices Sep 1976;5(11):277]
A member hospital reported that the mattress on which a patient was
receiving radio-frequency diathermy treatment began to smoke and burn. The treatment was
discontinued, and no injuries resulted. Subsequent investigation disclosed that the
mattress was the conductive type usually found in operating suites. Absorption of
radio-frequency energy by the mattress caused the dangerous temperature rise, and, as a
side effect, drastically diminished the therapeutic energy being delivered to the patient.
The radio-frequency electromagnetic field produced by diathermy units
heats the treated areas of the patient's body by inducing electrical currents to flow in
the irradiated tissues. The electromagnetic field is strongest near the application head
and the power cables feeding them but also pervades the entire area surrounding the
operating diathermy unit. Any conductor placed within this field will be heated, the
degree of heating depending on the local field strength and the conductor properties. For
this reason, diathermy manufacturers caution that all metal and other conductors be
removed from the treatment area.
Conductive mattresses are included in this caution but may not be
recognized as sources of danger, as is evident in the reported incident. In this case, the
cables powering the applicator head rested against the mattress and caused it to overheat.
- Inspect the mattresses used on your diathermy
treatment tables to determine if they are conductive. Conductivity may be
indicated by a label on the mattress.
- If no label is present, test for mattress
conductivity using a megohmmeter identical to that used in testing operating
room floors. A rough measurement can be made using an ohmmeter and standard
banana plugs or clip leads contacting two points on the mattress about six
inches apart. Be sure not to touch exposed metal on these meter leads with
bare hands. If the meter needle swings appreciably (to approximately 10-50
kilohms), the mattress is conductive.
- Replace all conductive mattresses on diathermy treatment tables with
ones that are nonconductive.
- Diathermy Units [11-244]
- Mattresses, Operating Table [12-478]
Cause of Device-Related Incident
Device factor: Device interaction
User error: Incorrect clinical use
Mechanism of Injury or