Sleep disruption is common in ICU patients and has been characterized by several studies using polysomnography (PSG) [1-3]. Adverse consequences of sleep disruption include impaired immune function, decreased inspiratory muscle endurance, negatively affected weaning from mechanical ventilation, and a possible association with delirium and severe morbidity [4,5]. The causes of sleep disruption in the ICU are multifactorial. The ICU environment is thought to be an important factor in sleep disruption [6].
Numerous studies have found excessive noise levels in the ICU, often with nighttime peaks of more than 80 dB(A) [5,7]. In addition, subjective and objective studies both demonstrate that patients have been disturbed by ICU noise [1,8-10]. Light exposure is another important sleep disruptor in ICU settings. Reported nocturnal illumination in ICUs varies widely, with mean maximum levels of 5 to 1400 lux [5,11]. Light exposure is the primary external cue for circadian rhythm. In addition, nocturnal melatonin secretion can be acutely suppressed by light, and 100 lux is sufficient to impact nocturnal melatonin secretion [12]. Throughout the past decade, evidence has been accumulating for the altered secretion of melatonin in ICU patients. ICU patients suffer from a severe lack of sleep associated with loss of the nocturnal melatonin secretion pattern [13,14]. Therefore, effective interventions to promote sleep in ICU patients are urgently needed.
Despite many claims that the use of noise reduction and lighting practice in an intensive care environment may improve the patient's sleep quality, there have been few objective studies to evaluate the effects of these interventions [15-17]. Most research in this area has focused purely on noise reduction and not explored the combined effects of ICU noise and light factors on physiological and psychological outcomes, including sleep architecture, perceived sleep quality and hormone secretion (melatonin and cortisol). No studies have yet evaluated the effects of earplugs and eye masks on the sleep of ICU patients as measured by PSG and hormone secretion.
We hypothesized that patients' sleep is disrupted by the noise and light in the ICU, accompanied by impaired nocturnal melatonin secretion and elevated cortisol secretion. Earplugs and eye masks worn during exposure to a simulated ICU environment may improve sleep and protect nocturnal melatonin and cortisol secretion. To test this hypothesis, an experimental study was conducted in a sleep laboratory.
