Evidence that mobile phones can interfere with vital intensive care equipment has been strengthened.
Doctors want bans relaxed
More than half the hospital ventilators tested by Dutch researchers stopped working properly when a mobile was switched on nearby.
The government has said current bans on the use of mobile phones in hospitals can be relaxed.
But the Critical Care journal study suggests it would be folly to do this in high dependency areas.
A total of 61 different medical devices were tested, and the majority could be affected by the presence of a mobile.
In particular, nine intensive care ventilators were checked, and seven of these could be "influenced" by mobiles.
Of these, six were described by the researchers as "hazardous", involving a direct physical influence on the patient.
Critical care monitors were also vulnerable, with seven out of 13 disrupted by mobile signals, while three out of seven syringe pumps were affected.
Other devices which suffered problems were dialysis machines, external pacemaker machines, feeding pumps and even air humidifiers.
Close range threat
"3G" mobiles were less likely to cause problems compared with second generation mobiles, and while, on average, the mobile had to be only a few centimetres away to interfere with the device, one "hazardous" incident happened at a distance of three metres.
The researchers wrote: "The policy to keep mobile phones one metre from the critical care bedside seems warranted."
In the UK, the Medicines and Healthcare Products Regulatory Agency (MHRA) advises that mobiles should be kept out of areas with sensitive medical equipment.
A spokesman said: "We recommend that mobile phones are not used in critical care areas such as intensive therapy units (ITU), special care baby units (SCBU) or where patients are attached to complex devices, as any effect on such equipment could be extremely detrimental to patient care."
Concerns over this issue led many trusts in the UK to issue blanket bans on mobile use in hospitals, but patient groups and many doctors have been campaigning for this to be reversed.
Earlier this year, junior Health Minister Andy Burnham said that hospitals could relax these rules.
Many trusts have now done this, although some have kept the ban over fears that patient privacy could be breached by the latest camera phones.
The British Medical Association has maintained that there is no significant evidence linking mobiles to problems with medical devices, and said that patients would benefit from doctors being able to communicate better with colleagues while on the wards.
A spokesman said: "If new evidence comes out, we will look at it, but doctors say that it can be very useful to them to make and receive work-related calls this way."