In 1999, Jewett and colleagues conducted a study examining the effect of sleep inertia on cognitive throughput in a lab setting. This study required subjects to complete a test battery at regular intervals following awakening. The test battery contained visual analog scales to assess subjective feelings of sleepiness and an addition task. The researchers compared ratings of sleepiness and performance on the addition task to overall mean performance on the tests. They found that both subjective ratings of sleepiness and cognitive throughput (from the addition task), were far below mean scores upon awakening (figure a & b to the left). Interestingly, the results of this study also show that study participants felt fully alert before their performance on the addition task reached mean performance, suggesting that people feel alert before they are fully cognizant.

Clearly, sleep inertia effects can be extremely dangerous in medicine where housestaff are often paged from sleep in call rooms to make quick decisions in emergency situations.

One resident reported the following frightening example of how sleep inertia affected his cognitive abilities when awakened from a nap while on call:

When I was a second-year resident working in the pediatric intensive care unit,
I had an experience one night that brought home to me the profound effects of
sleep inertia.  At around 1:00 in the morning, the unit was unusually quiet, and
I was able to slip away for a few minutes to nap in the cramped call room
located in the back of the unit.  Shortly after falling asleep, I reportedly
received a phone call from a colleague working on the general pediatric floor,
informing me that he had a 9 year old girl with asthma on his service who had
become critically ill and required immediate transfer to the ICU to be
intubated.  After speaking with him for 1-2 minutes on the phone, I must have
rolled over and gone back to sleep, because the next thing I knew he was shaking
me awake, telling me, "Get up! Get up!  She needs to be intubated right now!"  I
had no recollection whatsoever of our recent phone call, and to this day, do not
recall it.  Still disoriented after being shaken awake, I jumped from my bed,
ran across the hall to the bathroom, and began brushing my teeth.  I emerged a
few minutes later, finally somewhat aware of my surroundings, to find that a
senior trainee had stepped up in my absence and intubated the little girl;
fortunately, she was doing fine.  Awakening in this circumstance, however, was
both frightening and eye-opening for me.  It was the first time I began to
seriously question the safety of a work schedule that put me in such situations
as often as two to three times per week for three years.  This time the patient
was lucky - someone else was there to help.  The next patient, however, might
not be so lucky.

The best way to mitigate the effects of sleep inertia with modified scheduling is to reduce a resident’s need for sleep while on call.  By reducing the pressure to sleep, the effects of sleep inertia will not be as dramatic.  This can be achieved by limiting the duration of time a resident is required to work at night.  In a HWHHS group study which limited night call work to <16 hours, residents were able to nap prior to night duty. Residents who took a prophylactic nap before coming into work often reported that even when there was time to take a nap overnight, they did not feel they needed to sleep and were able to use the extra time productively on the unit.  By reducing the extreme pressure to sleep at night, there are fewer opportunities for sleep inertia to occur at all.