Sleep inertia, the grogginess and disorientation experienced on waking, does affect the cognitive performance of physicians woken from on-call naps during nightshifts.

However most of the effect dissipates relatively quickly – returning to normal functional capacity within about 12 minutes of waking.

Research presented at the Sleep DownUnder 2019 conference in Sydney by Australian Dr Raymond Matthews, involved 43 anaesthetists working across 75 overnight shifts in ICU in a major hospital in Sweden.

Dr Matthews is a sleep and fatigue researcher at the Behaviour Brain Body Research Centre at the University of South Australia and a post-doctoral research fellow at the Karolinska Institute in Stockholm, Sweden.

During the night shifts, sleep was measured using polysomnography via a portable sleep monitor.

The variety of performance measurements, presented in a randomised order, included a three-minute Stroop, spatial memory, word memory and mental arithmetic tests.

The study found 5% of doctors were too impaired to complete the tests on being woken, many more doctors (15%) did not sleep at all, and 25% were woken by a real call before they could be tested.

Of the remaining nightshifts, an unexpectedly low proportion (42%) of doctors were woken from slow wave sleep, which is known to be associated with sleep inertia.

The finding suggests that sleep architecture is affected in physicians on call.

The study also found tests conducted at 0-3 minutes and 3-6 minutes after waking on night shift were significantly worse than all other tests.

Tests conducted at 0-3 minutes, 3-6 minutes and 6-9 minutes after waking from slow wave sleep were worse than those conducted after non-slow wave sleep or during ‘awake’ tests.

The study confirms slow wave sleep is the main factor associated with performance impairment upon waking.