During the current national and international literature review, the studies were seen to mostly focus on subjects such as circadian rhythm and psychological disorders and problems, obesity, cancer, etc. No studies were found on the effect of nursing care provided according to circadian rhythm. Therefore, it is thought that determining chronotypes and providing appropriate nursing care is important to prevent pain, sleep, delirium and many physiological parameters and comorbid diseases, especially in intensive care patients, in terms of maintaining the circadian rhythm.

The study population will consist of patients treated in the Coronary Intensive Care Unit of Sakarya University Training and Research Hospital. A total of 32 patients will form the sample of the study, including 16 in intervention and 16 in a control group that agree to participate in the study and meet the study criteria. In terms of the reliability of the study results, the patients in this study will be allocated to the groups with a stratified randomization method. Patients will be randomly matched to the intervention (I) and control (C) group according to their gender, age, and circadian rhythms. Data will be collected after obtaining the institution's permission, the approval of the Ethics Committee, and the patients' consent through a face-to-face interview with patients. Firstly, the patients will be evaluated after admitted to the intensive care unit, and the intervention and control group will be formed using a stratified randomized method from those meeting the study criteria. All surveys that will be used in the study will be applied to both groups during the first interview. According to their chronotype, the intervention group will then be given sleeping glasses and earplugs at night for those who are in the morningtype, and till afternoon during the day for those who are in the eveningtype. Moreover, patients in the intervention group will be given 5000 Lux daylight(Maldonado, 2017) during the time they are awake depending on their circadian rhythms. An Android smartwatch will be used to determine patients' sleeping and waking up times, sleep quality and sleep depth. Nursing care will also be provided when patients are awake per their chronotype. Before the study, intensive care nurses will be trained to provide appropriate care according to the circadian rhythm and chronotype to have consistency in the care. Patients will be observed for three days and during this time cortisone and melatonin levels will be checked in both control and intervention groups (this test is not provided regularly but it will be paid by the financial sponsors). At the end of the third day, surveys will be conducted once again with both groups. All through this time, the control group will not have any interventions, only the standard ICU care to be provided.

In the study, "Patient Information Form, The Richards-Campbell Sleep Questionnaire, the Sleep Quality Scale which is planned to be developed, Intensive Care Delirium Screening Checklist, Horne and Ostberg Morningness-Eveningness Questionnaire, Daily Rhythm Questionnaire, Hospital Anxiety and Depression Scale" will be used as a part of the pre-test. Three days later, "Patient Information Form, The Richards-Campbell Sleep Questionnaire, the Sleep Quality Scale which is planned to be developed, Intensive Care Delirium Screening Checklist, Horne and Ostberg Morningness-Eveningness Questionnaire, Daily Rhythm Questionnaire, Hospital Anxiety and Depression Scale" will be applied to the patients as a part of the post-test.

As part of this study, a new scale specific to intensive care patients will be developed. The effects of nursing care given in accordance with the circadian rhythm, which has not been investigated before, on sleep quality, pain, delirium, and anxiety will be revealed.