Effects of alterations of inspiratory oxygen fractions on heart rate variability

Changes in heart rate variability (HRV) during anaesthesia depend on multiple influences such as hypnosis, analgesia, surgical stress, and interacting drugs. Several recent studies have aimed to establish HRV-based monitoring tools to measure perioperative stress or anaesthetic depth. Although hyperoxic ventilation (HV) is known to alter autonomic cardiovascular regulation, there have been no studies investigating its influence on time- and frequency-domain analysis during general anaesthesia. Therefore, we have examined the effects of HV on cardiovascular neuroregulation of anaesthetized patients and conscious volunteers by analysis of relevant HRV parameters.

Fourteen healthy volunteers and 14 anaesthetized, ventilated ASA I patients sequentially breathed room air ( 0.21), pure oxygen ( 1.0), and then room air. During each episode, standardized HRV parameters were calculated from 5 min ECG recordings.

HV significantly reduced HR and increased the standard deviation of RR interval values, the root mean square of successive RR interval differences, and the high-frequency (HF) power of the spectral components, whereas the low-frequency (LF) power and the LF/HF ratio of HRV were reduced in both groups. All changes were reversible after was reduced to normoxia.

In both healthy volunteers and anaesthetized patients, HV resulted in comparable and reversible changes of established HRV parameters. These changes might be relevant enough to bias HRV-based analgesia and anaesthesia monitoring and could result in a clinically relevant misinterpretation of HRV parameters as indicators of anaesthetic depth during HV.