Respiratory induced heart rate and blood pressure variability during mechanical ventilation in critically ill and brain death patients

We analysed respiratory induced heart rate and blood pressure variability in mechanically ventilated patients with different levels of sedation and central nervous system activity. Our aim was to determine whether it is possible to distinguish different levels of sedation or human brain activity from heart rate and blood pressure. We measured 19 critically ill and 15 brain death patients ventilated at various respiratory frequencies - 15, 12, 8 and 6 breaths per minute. Basal and deeper sedation was performed in the critically ill patients. We detected and analysed heart rate and blood pressure parameters induced by ventilation. Results: Respiratory induced heart rate variability is the unique parameter that can differentiate between brain death patients and sedated critically ill patients. Significant differences exist, especially during slow deep breathing with a mean period of 10 seconds. The limit values reflecting brain death are: baroreflex lower than 0.5 ms/mmHg and tidal volume normalised heart rate variability lower than 0.5 ms/ml. Reduced heart rate variability parameters of brain death patients remain unchanged even after normalisation to respiration volume. However, differences between basal and deep sedation do not appear significant on any parameter.