Profile of autonomic cardiac control in patients who are not considered ready for weaning from mechanical ventilation

This study tracks the global tendency of the heart rate variability (HRV) profile over five ventilation modes, aiming to find evidences on the hypothesis that patients who failed during the weaning process manifest important differences in the autonomic nervous system activity. This preliminary study enrols 17 patients (7 successful (S), 10 failure (F)) who underwent weaning with AVEA ventilator. Time- and frequency- domain HRV analysis is applied over 5-min ECG episodes recorded at the beginning of 5 ventilation modes: (1) controlled mechanical ventilation (CMV) on a sedated patient; (2) CMV on a sedated and paralyzed patient; (3) Pressure support ventilation with zero back-up pressure PSV(0); (4) PSV at 12-25 cmH₂O; (5) Spontaneous breathing trial (SBT) at 8 cmH₂O. Our results support the finding of other authors that during SBT, the patients who succeed in weaning show a prevalently sympathetic modulation, while relatively increased vagal activity is typical for the F-group. PSV(0) is however an outstanding test for which F-patients manifest about 3 to 20 fold increased sympathetic and vagal activity compared to the S-group.