The quality of sleep is poor in many patients admitted to an intensive care unit (ICU) [1-4]. Many factors contribute to this problem. Environmental factors such as light, noise, and inadequate room temperature and psychological factors such as fear, anxiety, and pain play important roles [5-7]. In addition, the severity and acuity of the critical illness itself may also contribute to sleep disturbance [7]. Sleep disturbance is associated with many physiological consequences that may negatively affect the prognoses of critically ill patients [8].

Unfortunately, sleep assessment in the ICU can be challenging. Polysomnography, the gold standard for sleep assessment in stable patients, is impractical in the ICU setting [5,9]. Self-reported subjective assessments offer an alternative approach. Among the subjective tools, the Richards-Campbell Sleep Questionnaire (RCSQ) is the most validated and reliable tool [10]. The RCSQ consists of five questions assessing sleep depth, latency, and fragmentation, as well as time to the resumption of sleep and total sleep quality [11]. The scores are measured with a 100-mm visual analog scale (VAS), and higher scores indicate better sleep [5,12,13]. The RCSQ has been translated from English to other languages, including German, Swedish, Spanish, and Chinese [12-15], to be easily incorporated into multiple clinical practices.

Despite growing concerns regarding poor sleep quality in the ICU, there is scarce literature available on sleep quality in the ICUs of Asian countries. Therefore, this study aimed to evaluate the internal consistency of the Korean version of the RCSQ (K-RCSQ) in the medical ICU (MICU) setting.

A total of 52 patients was enrolled during the study period (46 patients in a tertiary care and 6 patients in a secondary care hospital). Patient characteristics at the time of enrollment are shown in Table 1. Thirty patients (57.7%) were men, and the mean age of the patients was 62.8 ± 15.9 years. Reasons for ICU admission were respiratory failure (49.2%), cardiologic failure (15.4%), renal failure (13.8%), and sepsis (10.8%). The mean Acute Physiology and Chronic Health Evaluation (APACHE) II score was 17.5 ± 7.3, and the Sequential Organ Failure Assessment (SOFA) score was 7.3 ± 4.3. At the time of RCSQ assessment, three patients (5.7%) were under light sedation. One patient had been given propofol (72 mg/kg/day), and two were sedated with dexmedetomidine (16.8 μg/kg/day and 4.8 μg/kg/day, respectively). A total of eight patients (15.4%) had been given opiates for pain control. One patient had received a fentanyl patch (75 μg/hr), and the other seven had been given remifentanil (mean, 57.6 μg/kg/day). Most patients (80.8%) were alert and calm at enrollment, with an RASS score of 0. The median length of ICU stay was 4 days (range, 1–21 days). At the time of discharge from the ICU, 43 patients (82.7%) were capable of only limited selfcare or were completely disabled (Eastern Cooperative Oncology Group Performance Status 3 or 4).

The mean score of the five items of the K-RCSQ was 41.9 ± 28.9 (range, 0–100) (Table 2). Only eight patients (15%) showed very good sleep (scores > 75), while 16 patients (31%) had a K-RCSQ score less than 26, which indicated very poor sleep [12]. The overall internal consistency of the five items of the K-RCSQ was 0.96. Of the K-RCSQ subscales, the “sleep depth” domain had the highest mean K-RCSQ score, and the “returning to sleep” domain had the lowest K-RCSQ score. The mean score of perceived noise assessment was 40.7 ± 28.1 (range, 0–90). There was a significant linear correlation between noise score and average K-RCSQ score (r = –0.37, P < 0.001). The perceived noise score was significantly lower in the good sleep group (K-RCSQ score > 50) than in the poor sleep group (K-RCSQ score ≤ 50) (28.75 ± 26.35 vs. 48.28 ± 26.99, P = 0.014).

Sleep quality in critically ill patients is markedly abnormal. These patients frequently experience prolonged sleep latency, sleep fragmentation, and frequent arousal [8]. Despite growing concerns regarding sleep disturbance in the ICU and its physiological consequences, there are only a few studies on sleep quality among critically ill Korean patients [19-22]. Only one study used polysomnography to assess the sleep quality of five patients [21], while other studies used sleep questionnaires. However, sleep questionnaires, such as the Overran-Snyder-Halpern sleep scale, are not adequately validated in critically ill patients after comparison with polysomnography data [10]. To the best of our knowledge, there are no published studies assessing sleep quality of patients in Korean ICUs using the RCSQ, which is currently considered the most validated and reliable tool [10].

In this study, the K-RCSQ showed excellent reliability with an internal consistency of 0.960 by Cronbach’s alpha. The Cronbach’s alpha of the original English version was 0.90 [11]. This result is comparable to that of other versions of the RCSQ. The Cronbach’s alpha of the Swedish [13], German [12], Spanish [14], and Chinese [15] versions was 0.92, 0.88, 0.89, and 0.923, respectively. The K-RCSQ is a reliable tool that can be used for subjective measurements of sleep quality in Korean ICUs.

Subjective sleep quality was low in our study population. The mean K-RCSQ score was 41.9 ± 28.9, which is slightly lower than the RCSQ scores collected from the ICUs of various countries [12,14,23]. One possible explanation is that the study population had more severe medical conditions. Moreover, different ICU settings, such as single- or multi-bed rooms, could have influenced the results. Single-bed rooms were available to only a few patients in our study population. Among the sleep domains, the lowest score was observed in RCSQ 4 (returning to sleep), with a mean of 40.1 ± 34.7. Scores from each sleep domain and the domain with the lowest score vary widely from study to study. Returning to sleep was one of the top-rated issues of the RCSQ in ICUs of several countries [12,14,16]. Studies from Sweden [13] and China [15] showed that returning to sleep was the third highest rated item. A study from Czech [24] showed that returning to sleep was the lowest rated sleep domain, similar to the results of the present study. There are many possible causes for difficulty in returning to sleep, such as noise and anxiety, and further studies are needed to clarify the cause and effect of these findings.

Critically ill patients are surrounded by many devices that generate loud alarms and noises that may result in disruption of sleep [4]. Results from our study suggest that there is a correlation between perceived noise level and quality of sleep in critically ill patients. An interventional study of ICU patients also showed that improvements in perceived noise score correlated with improvements in RCSQ score [24]. Consciousness of the noise level in the ICU is important because noise reduction may be a feasible nonpharmacological strategy to improve sleep and delirium in the ICU [8].

There are several limitations to this study. First, the validity of the K-RCSQ was not directly assessed. The K-RCSQ was not compared with an objective measurement of sleep. Polysomnography is impractical to use in the ICU, and the RCSQ has been validated against polysomnography, showing moderate correlation [11]. Second, noise in the ICU was not recorded, and the noise level was assessed subjectively. Third, the included patients from the MICU may not appropriately represent the general critically ill population. However, severely ill patients, including those under mechanical ventilation, were able to answer the K-RCSQ. Moreover, the RCSQ is widely used in cardiovascular ICUs [11], heterogenous ICUs [12] and surgical ICUs [13,14]. In conclusion, the K-RCSQ had excellent reliability (internal consistency). This simple tool may help assess the sleep quality of critically ill patients and improve the quality of ICU care.