Preoperative daytime sleepiness tracked with worse cognition six weeks after surgery

Design

Prospective observational cohort with home sleep apnoea testing and pre- and postoperative cognitive testing

Population

96 older non-cardiac surgery patients, of whom 11 had moderate to severe excessive daytime sleepiness

Primary outcome

Change in a global cognitive index from before surgery to 6 weeks and 1 year after

Effect

Mean difference in 6-week global cognition -0.24 (95 per cent CI -0.48 to -0.004, P = 0.046); peak delirium severity OR 3.66 (0.96 to 13.91, P = 0.057)

Ninety-six older patients having non-cardiac surgery completed Epworth Sleepiness Scale questionnaires, home sleep apnoea testing, and delirium and cognitive assessment before and after surgery, with cognitive scores combined into a single global index. Eleven had moderate to severe excessive daytime sleepiness, defined as an Epworth score above 12.

Adjusted for age, sex, respiratory event index, baseline cognition and surgery duration, those 11 patients had a worse change in global cognition at six weeks (mean difference -0.24, 95 per cent CI -0.48 to -0.004, P = 0.046). Peak postoperative delirium severity did not reach significance (odds ratio 3.66, 0.96 to 13.91, P = 0.057), though the direction was the same.

Eleven exposed patients is a very small number to build anything on, and both results sit right at the boundary - one just inside, one just outside. What makes it worth reporting is that the sleepiness signal survived adjustment for the respiratory event index, meaning it is not simply undiagnosed sleep apnoea doing the work. Excessive daytime sleepiness is already associated with neurodegeneration and cognitive decline, and the plausible reading is that it marks a brain with less reserve rather than causing anything. The Epworth takes two minutes and is free, which makes it a reasonable thing to add to a preoperative assessment in an older patient while larger studies are awaited.

• Add the Epworth Sleepiness Scale to preoperative assessment in older patients; it costs two minutes.
• Treat a score above 12 as a marker of vulnerability, not as a diagnosis or an indication to postpone.
• Note the finding held after adjusting for sleep apnoea severity, so it is not simply undetected apnoea.
• Do not overstate this: 11 exposed patients and P values of 0.046 and 0.057.
• Where sleepiness is found, investigate it on its own merits regardless of the surgery.

The statistics, in plain English

A confidence interval running to -0.004 means the result only just excludes no effect, and with 11 exposed patients it would take very little to move it either way. The delirium result, at P = 0.057 with an interval of 0.96 to 13.91, is a non-finding in a sample far too small to settle the question - it should not be reported as showing no association. This is a prospective observational cohort, so the association identifies a vulnerable group and says nothing about whether treating sleepiness would help.

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