Variations of the analgesia nociception index during general anaesthesia for laparoscopic abdominal surgery

The analgesia nociception index (ANI) is an online heart rate variability analysis proposed for assessment of the antinociception/nociception balance. In this observational study, we compared ANI with heart rate (HR) and systolic blood pressure (SBP) during various noxious stimuli in anaesthetized patients. 15 adult patients undergoing laparoscopic appendectomy or cholecystectomy were studied. Patients received target controlled infusions of propofol (adjusted to maintain the Bispectral index in the range [40-60]) and remifentanil (with target increase in case of haemodynamic reactivity [increase in HR and/or SBP >20% of baseline]), and cisatracurium. Medical staff was blind to the ANI monitor. ANI and haemodynamic data were recorded at predefined times before and during surgery, including tetanic stimulation of the ulnar nerve before start of surgery. Anaesthesia induction decreased HR and SBP, while high ANI values (88 [17]) were recorded, indicating parasympathetic predominance. In 10 out of 11 patients, tetanic stimulation led to a transient (<5 min) decrease in ANI to 48 (40) whereas HR and SBP did not change. After start of surgery, ANI decreased to 60 (39) and decreased further to 50 (15) after the pneumoperitoneum was inflated, while there was no significant change in HR or SBP. When haemodynamic reactivity occurred, ANI had further decreased to 40 (15). After completion of surgery, ANI returned to 90 (34). ANI seems more sensitive than HR and SBP to moderate nociceptive stimuli in propofol-anaesthetized patients. Whether ANI monitoring may allow preventing haemodynamic reactivity to noxious stimuli remains to be demonstrated.