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home : columns : ask the doctors February 24, 2018

2/13/2018 8:12:00 AM
Study suggests time of day may have effect on surgical outcome

DEAR DOCTOR: It seems like doctors always want to schedule surgeries as early as possible. But I recently read that heart surgery survival chances are better in the afternoon. Why would this be? Should people push their doctors for afternoon surgeries?  

DEAR READER: You're referring to the results of a study published in the journal Lancet last month. Over the course of six years, scientists from the University of Lille in France examined the medical data of close to 600 patients who underwent a heart surgery known as aortic valve replacement. In this surgery, the aortic valve, which regulates blood flow to the heart, is replaced with either animal or synthetic tissue. What the researchers wanted to know was whether the time of day that these surgeries took place played a role in which patients went on to experience serious complications.  

The results were surprising. Researchers found that patients whose surgeries were performed after noon had half the risk of heart attack, acute heart failure or death in the 500 days after surgery than did those whose procedures took place in the morning. A separate analysis of 44 patients who had morning surgery, and 44 who had afternoon surgery, examined the rate of a certain type of tissue injury that can occur when the patients are taken off bypass during the operation and blood flow returns to the repaired structures of the heart. Once again, the patients with afternoon surgeries fared measurably better than those with morning surgeries.

These findings seem to add to a growing body of evidence that circadian rhythms -- that is, our biological clocks -- have an effect on health care interventions. Previous studies in mice have suggested that the body responds best to chemotherapy during certain times of day. A large-scale study into flu shots found that, among older people, those who received the vaccine in the morning produced more antibodies than those who got an afternoon injection.  

Ongoing research continues to show that circadian rhythms play a role in all aspects of physical and mental health. Here at UCLA, scientists are looking into the connection between chronic disruption of circadian rhythms, as in workers on swing or night shifts, and the increased risk of developing diabetes and metabolic syndrome. Previous research has shown that circadian disruption affects learning, mental and emotional health, and can even lead to death. This line of inquiry is considered to be so important that last year the Nobel Prize in Medicine went to three researchers who identified the molecular mechanisms that control our body clocks.

That said, there are certain caveats regarding this new heart surgery study. As an analysis by the National Institutes of Health notes, 600 patients make a small sample size. Each of these patients was treated at the same hospital, which begs the question whether it was the time of day of the surgeries, or the specific surgical teams that performed them, that had the greatest effect on the outcomes.  

We need additional studies in multiple medical sites, and with a diversity of heart procedures, before we can conclusively link time of day to better surgical outcomes.

(Eve Glazier, M.D., MBA, is an internist and assistant professor of medicine at UCLA Health. Elizabeth Ko, M.D., is an internist and primary care physician at UCLA Health.)

(Send your questions to, or write: Ask the Doctors, c/o Media Relations, UCLA Health, 924 Westwood Blvd., Suite 350, Los Angeles, CA, 90095. Owing to the volume of mail, personal replies cannot be provided.)

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