Endogenous melatonin is produced by the pineal gland at night under normal conditions and regulates the sleep-wake cycle. Artificial light administered at night suppresses melatonin production and sleep disturbances are accompanied by abnormal melatonin secretion such as phase delay. Therefore, dramatic disturbances of endogenous rhythms in intensive care unit patients have remarkable effects on melatonin production. In addition to its physiological roles in regulating sleep patterns, melatonin has been demonstrated to provide antiinflammatory effects in experimental models. Although some previous studies have investigated the circadian pattern of melatonin in intensive care unit patients, the investigators think that the present study is the first one that will assess the effects of controlling noise and light on melatonin and inflammatory response after major abdominal surgery.

This study is going to be conducted in accordance with the Helsinki Declaration and has been approved by Eskisehir Osmangazi University Ethics Committee. Forty consecutive patients, aged 18-65, who will undergo elective major abdominal operations will be enrolled in the study after obtaining informed consent. All patients will receive adequate postoperative pain management with the Pain Buster ® system and patient-controlled intravenous analgesia (PCA). The patients will be randomly assigned to either the experimental group or the control group. The control group will receive the usual care. The patients in the experimental group will be screened in the side-rooms where normally the patients who either have infections or are at risk of infection, are nursed. The study intervention will include dimming the lights to 40 lux and closing the doors of the side-room to decrease the noise level below 40 decibels (dB) between 11:00 p.m.-5:00 a.m.

Inclusion Criteria:

• Patients undergoing elective major abdominal surgery

Exclusion Criteria:

• Any evidence of inflammatory diseases during the postoperative care (e.g. anastomotic leakage)