September 7, 2017

expert reaction to study investigating the ‘weekend effect’ in Intensive Care Units (ICUs) in Austria

In a new study published in Critical Care scientists report that a person’s risk of dying is higher if they are admitted to Austrian intensive care units (ICUs) at the weekend compared to during the week. However, if patients are simply just in the ICU at the weekend, then the death rate was lower.

Dr Amy Mason, incoming Applied Statistician in the Department of Public Health and Primary Care, University of Cambridge, said:

“This large, statistically robust study from Austria shows an apparent contradiction – that admission on the weekend has a higher death rate than admission on a weekday, while simply being in intensive care unit (ICU) at the weekend has a lower death rate than during the week. This “contradiction” is common in weekend effect studies and appears in other papers, including the well-known Freemantle study on emergency admission mortality rates in UK hospitals.

“It is still not known what causes this weekend effect. There are many possible reasons – patients are more ill when they arrive at the ICU on the weekend, proportionally fewer planned surgeries happen, and there are differences in care.  The suggestion here that the lower death rate may be caused by not discharging less ill patients during the weekend would go some way to unravelling the apparent contradiction. It would be interesting to know if UK data showed a similar pattern.

“In Austria, some specific interventions were less likely to occur at weekend, whereas interventions in general were happening at a higher rate. This is another apparent contradiction and it is unclear whether this difference in care is caused by solely by differences in individual patient needs or instead by limited resources within the Austrian ICUs. However the paper doesn’t directly show that changes in interventions at the weekend impacted patient mortality – without that causal link it is impossible to say that the higher death rates are conclusively caused by lower quality of care.

“The most recent study of NHS ICU admissions did not find any increase in death rates due to admission at the weekend, and these new results do not generalise to NHS. However, this new study fits within a body of evidence that the weekend effect is observed in many countries and that it is unclear whether lower quality of care or patients being more ill at the weekend is the dominant cause of each effect.”

* ‘Weekends affect mortality risk and chance of discharge in critically ill patients: a retrospective study in the Austrian registry for intensive care’ by Zajic et al. published in Critical Care on Thursday 7 September.

Declared interests

Dr Amy Mason: “I recently published a paper on the weekend effect in the Lancet – http://www.thelancet.com/journals/lancet/article/PIIS0140-6736(17)30782-1/abstract I was employed until Dec 2016 by the Nuffield Department of Medicine, University of Oxford, in part to investigate weekend effects within Oxford University Hospitals.”