Delirium in patients with hip fracture is associated with increased heart rate variability

Background Heart rate variability (HRV) is a method to assess the autonomic nervous system and reflects possibly central brain states. HRV has previously not been examined in patients with hip fracture and delirium. Aims To explore HRV parameters in hip fracture patients with and without delirium. Methods Patients admitted to Oslo University Hospital with hip fracture and sinus rhythm in electrocardiogram (ECG) were included. Delirium was diagnosed using the confusion assessment method. HRV was assessed preoperatively after a relaxing period of five minutes, by measuring an ECG signal over 5 min. Parameters in time domain (the standard deviation of the QRS distances-SDNN) and frequency domain (total power (TP), low frequency (LF), high frequency (HF) and LF/HF ratio) were calculated. Results Seventy-five patients were included in the study, and 21 of them had subsyndromal delirium and were excluded from the analysis. Fifty-four patients with a mean age of 83.5 years (SD 8.6, 78% females) were included. Twenty-six patients (48%) had preoperative delirium, 11 (20%) developed delirium postoperatively, whereas 17 (31%) never developed delirium. SDNN, TP and HF values were significantly higher in patients with delirium compared to patients without delirium, and LF and LF/HF were lower. Patients developing postoperative delirium had decreased LF and increased HF before symptom onset. Discussion Increased SDNN, TP and HF and decreased LF values might reflect an abnormal stress response in delirium. Conclusion HRV measurements in patients with hip fractures provide additional information beyond heart rate and might be used to identify relevant pathophysiological factors in delirium.