Influence of Variations of Systemic Venous Return on Analgesia Nociception Index (ANI) During General Anaesthesia

In the context of opioid sparing goal during general anaesthesia, the Analgesia nociception index (ANI) is an analgesia/nociception balance monitoring tool computed from high frequency heart rate variability analysis, and developed by MetroDoloris (Lille, France). Its sensitivity to detect noxious stimulus was studied in several studies. However, its specificity is not established in particular in the presence of factors influencing autonomic nervous system other than analgesia/nociception balance. In the context of anaesthesia, one of the most relevant factor is hypovolemia. This study aims to assess the effect of blood volume variations on ANI under general anaesthesia, independently of analgesia/nociception balance status. Variations of systemic venous return (SVR) (cardiac preload), which reflects blood volume status, will be induced by changes of operating table slope, from head-down tilt (Trendelenburg), with increased SVR, to head-up tilt position, with decreased SVR. Variations of SVR will be attested by changes in the arterial pulse pressure variation, a well-established indice of preload responsiveness in the mechanically ventilated anaesthetized patient.

Inclusion criteria

• neurosurgical operation requiring invasive monitoring of arterial blood pressure

Exclusion criteria

• pacemaker, arrhythmia
• chronic medication with beta blocker
• possible disorder of autonomic nervous system: diabetes, alcoholism, chronic pain
• anticholinergic drug administration before measures
• intracranial hypertension
• no social security coverage
• pregnancy