The woman's gall bladder had been removed without incident 12 hours earlier, but now her blood pressure was dropping and her heart rate was increasing.
Her bedside nurse put in a call.
Within minutes, the hospital corridors were filled with the clamour of feet. It was the rapid response team, coming to the rescue.
An intensive care doctor and nurse quickly worked out that the woman, 40, was bleeding and steering towards cardiac arrest.
They administered an urgent blood transfusion and the patient survived.
This situation, which happened at Liverpool Hospital recently, is among thousands in which lives have been saved because medical staff have quickly identified and responded to patients in danger of cardiopulmonary arrest.
Devised by University of NSW professor Ken Hillman, the rapid response system is now mandatory in NSW and has been adopted around the world.
Professor Hillman's research indicates that the system saves 12,800 Australian lives annually.
His study of 9 million hospital admissions, published in the Medical Journal of Australia, quantified the reduction in cardiac arrests during a period in which an increasing number of hospitals were adopting rapid response systems.
The number of hospitals that practised the system doubled over the eight-year period, and there was a 50 per cent reduction in cardiac arrests and a 50 per cent fall in mortality associated with cardiac arrest.
"There aren't many more things in medicine that are associated with such a spectacular reduction," Professor Hillman said.
"These people were languishing in hospital and then they would die.
"So if for example you came in to hospital for a gall bladder operation but then you started bleeding after the operation, the people looking after you are very good at taking a gallbladder out but their team may not be very good at recognising someone who's bleeding or having a heart attack.
"80 per cent of people with cardiac arrest have slow deterioration over eight hours."
Professor Hillman was working as an intensive care specialist in London when the death of a 19-year-old woman galvanised his fury over the quantum of preventable hospital deaths.
She had been admitted to hospital with broken bones from a motorbike accident, but bled to death in the middle of a big teaching hospital because the staff failed to recognise the signs.
Although many cardiac arrests are preventable, their warning signs were not being detected quickly enough because the information had to be passed through a chain of command before it reached the experts in resuscitation.
Professor Hillman returned to Australia determined to bring about a system that notified intensive care specialists earlier to changes in the patient's condition.
His rapid response system empowered nurses to press a button to alert the intensive care unit if there was a change in a patient's vital signs.
Initially there was resistance.
The doctors in charge of the patients did not want to relinquish control.
The intensive care specialists were under-resourced for the increase in workload.
But Professor Hillman hammered his colleagues with anecdotes about preventable deaths until the fight melted away, and the results spoke for themselves.
Australian Resuscitation Council NSW chairman Paul Middleton said that while previously nurses could be reluctant to call doctors if a patient's vital signs slipped and doctors sometimes underestimated the significance of the change, rapid response systems had changed the way hospitals operated.
"What this has done is put a whole structure around the way we should do things," Dr Middleton said.
"It means the nurses have criteria to call people.
"In retrospect it seems straightforward. It's an absolutely stunning paper because the numbers involved and the changes seen are so huge that it really does make the point."