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The day of the week does not affect the survival chances of people undergoing emergency surgery, a study has suggested.

The University of Edinburgh said the findings challenged the results of previous research.

This indicated that those who undergo elective surgery at the end of the week are at a greater risk of dying.

However, the lead author of the previous research said this latest study lacked "statistical power".

Paul Aylin, professor of epidemiology and public health at Imperial College London, said the Edinburgh researchers had looked at about 50,000 admissions, compared to the 15 million cases examined in his study.

The University of Edinburgh team looked at emergency surgery cases in Scotland between 2005 and 2007.

They tracked patients' outcomes until 2012 and found that after adjustment for other risk factors, the day a patient received surgery had no effect on their short or long-term survival.

Patients who were admitted over a weekend were more likely to be operated on sooner, the study found.

'Weekend effect'

More than a third of all surgical procedures in the UK are classified as emergencies. Emergency patients are eight times more likely to die than those who elect to have surgery as they are more likely to experience complications.

Previous research has pointed to a "weekend effect" in which patients who undergo elective surgery on Saturdays or Sundays were more likely to die than those operated on during the week.

Prof Aylin suggested in 2013 that the higher risk of death could be because fewer doctors, nurses and many non-clinical staff were available at the weekend.

But the University of Edinburgh said its new study, published in the British Journal of Surgery, found no evidence to link day of the week to an increased risk of death for those undergoing emergency operations.

The researchers acknowledged they had examined a smaller number of cases than previous research but said theirs was the first to analyse a "complete national dataset".

The study was funded by the Chief Scientist's Office of Scotland.

Dr Michael Gillies, a consultant and associate medical director at the University of Edinburgh, said: "Emergency surgery is associated with far greater risks than elective surgery so it is reassuring to find that patients in Scotland are receiving the same high standards of care throughout the week."

But Prof Aylin disputed the results, saying a study sample of about 100,000 emergency admissions would be needed to detect a 10% increase in mortality.

"Given that the day of surgery is dependent on resources - staffing, theatre availability etc - clinical decision-making and workload, I would question whether the day of surgery is the most appropriate point of analysis," he said.

"The day of admission is perhaps more relevant. Also, by restricting analysis to patients who had an operation, the authors of the study have excluded patients who were admitted as an emergency, but who died before they could get to the operating table."

He added: "I would question the study's rational of only focussing on first admissions in three years- this automatically excludes a number of deaths, because by definition, if you are readmitted, you cannot have died in the index admission."