The traditional way of taking a pulse
A ban on hospital doctors wearing wristwatches could be potentially dangerous, say researchers.
Hospitals are about to implement a "bare below the elbows" dress code following advice from the Department of Health on how to cut infection risk.
Researchers asked doctors to estimate respiratory and pulse rates without looking at a second hand.
The Brtish Medical Journal study found estimates varied wildly when doctors had to rely just on judgement.
Under the government plans to combat infections such as Clostridium difficile and MRSA, doctors will not be allowed to wear long-sleeve shirts, jewellery or watches.
However, the researchers argue there is no evidence that wristwatches are carriers of infection.
They also warn that little account has been taken of their clinical benefits, particularly as most beds and examination couches in hospitals do not allow sight of a clock.
And they said fob watches have been found to be impractical for some clinical procedures.
The researchers asked 20 appropriately trained staff to evaluate different pulse and respiratory rates on a simulated patient without the use of a second hand.
Estimates for a pulse rate of 83 ranged from 60 to 120, and estimates for a respiratory rate of 14 ranged from 10 to 28.
The findings suggest that it was often not possible for healthcare professionals even to distinguish normal from abnormal without the use of a second hand.
Only one participant gave values for each reading that would not have been potentially dangerous.
The researchers argue their findings highlight the necessity for doctors to have sight of a second hand when assessing patients - especially in emergency situations where a clock might not be present.
They warn that if trusts wish to persist with the banning of wristwatches, they will be obliged to provide each bedspace with its own clock with a second hand.
Researcher Dr James Henderson, of Norfolk and Norwich University Hospital NHS Trust, said the issue could be a problem in areas, such as general wards, which were not geared up for patients taking an unexpected turn for the worse.
He said: "Many doctors assume they can tell if somebody is sick just by feeling their pulse, and we were surprised to find this may not be the case."
Mr Martin Shalley, an accident and emergency consultant at Birmingham Heartlands Hospital, was unconvinced by the findings.
He said: "If I was concerned about a patient I would use a machine to measure all these parameters formally."
Mr Shalley said persuading doctors to wash their hands more regularly would have a far bigger impact in helping to reduce transmission of infection.
A spokesman for the Department of Health said: "Patient safety must be paramount in everything the NHS does.
"A bare-below-the-elbows dress code for clinicians helps to support effective hand-washing and so reduces the risk of patients catching infections.
"It does not prevent clinicians from doing their job. We would expect clinicians to use clocks to measure pulse rates as this is good clinical practice."