Objective monitoring of pain during and after surgery has been elusive. Recently, Analgesia Nociception Index (ANI) monitor based on the high frequency component of heart rate variability has been launched into clinical practice. We monitored analgesia during craniotomy using ANI monitor and compared it with cardiovascular parameters and response entropy (RE) of entropy monitor.Materials and Methods:
In 21 patients undergoing a craniotomy for a supratentorial lesion, we monitored ANI, heart rate (HR), mean arterial pressure (MAP), state entropy, and RE throughout the surgery. Also, ANI, hemodynamic variables and spectral entropy values were noted at the times of maximal stimulation, such as induction, intubation, head pin fixation, skin incision, craniotomy, durotomy, and skin closure. We also compared ANI with RE during administration of bolus doses of fentanyl.Results:
There was an inverse correlation between ANI values and the hemodynamic changes. When the HR and MAP increased, ANI decreased suggesting a good correlation between hemodynamics and ANI values during the times of maximal stimulation. State entropy and RE did not change significantly in response to bolus doses of fentanyl administered during the course of surgery, while ANI increased significantly.Conclusion:
In neurosurgical patients undergoing elective supratentorial craniotomy, ANI measures response to noxious stimuli with at least as much reliability as hemodynamic variables and changes in ANI parallel the changes in HR and MAP. ANI is superior to RE for measurement of response to noxious stimuli.