Association Between Postoperative Delirium and Loss of Melatonin Rhythm After Hip Arthroplasty: A Pilot Study

The development of in-hospital postoperative delirium is one of the most common adverse complications in older patients. It can complicate the clinical course and prognosis, leading to patient deterioration. Its incidence is high, affecting up to 55% of patients undergoing procedures such as hip arthroplasty.

Thirty-four hospitalized patients aged 60 years and older with a diagnosis of hip fracture, but without delirium at admission, were included in the study. Daytime and nighttime saliva samples were collected one day before and one day after surgery. Pre- and postoperative melatonin levels were analyzed. Patients were then divided into two groups for comparison: those who developed delirium and those who did not.

Postoperative delirium was observed in 35.29% of patients. In the control group, salivary melatonin levels showed low concentrations during the day and high levels at night, indicating a preserved daily rhythm in melatonin secretion (F(1,33) = 82.639; p < 0.001). This pattern was consistent before and after surgery. In contrast, the delirium group also showed a diurnal rhythm with low morning and high evening melatonin levels before and after surgery, but without a statistically significant difference (F(1,22) = 0.225; p = N/A).

This study concludes that assessing melatonin levels during both light and dark phases is important to determine whether the circadian rhythm of melatonin secretion has been disrupted. This information may help guide the use of melatonin to prevent or anticipate the development of postoperative delirium.