Changes of heart rate variability during ventilator weaning.

STUDY OBJECTIVES Despite the recognition that ventilator weaning is associated with a change in autonomic nervous system activity, there has not been any report concerning the change of heart rate variability (HRV), a reliable method to detect autonomic nervous system activity, in patients during weaning. The aim of this study was to investigate the change of autonomic nervous system activity during ventilator weaning by HRV analysis. DESIGN Prospective study. SETTING A 16-bed medical ICU of a tertiary university hospital. PATIENTS Twenty-four patients receiving mechanical ventilation were included. Twelve patients with successful extubation after a spontaneous breathing trial (SBT) [T-piece trial] were classified as the success group; otherwise, the patients were placed in the failure group. INTERVENTIONS None. MEASUREMENTS AND RESULTS Variables, including the total power (TP), and the high-frequency (HF) and low-frequency (LF) components of HRV, were measured in three phases: assist/control mandatory ventilation, pressure support ventilation (PSV), and SBT. While shifting from PSV to SBT, the HRV components decreased significantly in the failure group (TP, p = 0.025; LF, p = 0.007; HF, p = 0.031), but not in the success group. CONCLUSIONS By HRV analysis, reduced HRV and vagal withdrawal of the autonomic nervous system activity are the main changes in patients with weaning failure.