The ANI (Analgesia Nociception Index) allows a direct measurement of the activity of the autonomic nervous system (ANS) through the analysis of its parasympathetic component via the respiratory sinus arrhythmia. Our index uses brief and rapid heart rate variations induced by each respiratory cycle (spontaneous or artificial) in order to quantify the parasympathetic tone.
Developed in order to provide clinicians a monitoring system of analgesia matching the requirements of routine clinical practice, in other words easy to use, easy to interpret, reliable and continuous… The ANI is a numerical value that evolves between 0 and 100. Our index quantifies the activity of parasympathetic part of the autonomic nervous system.
ANI has been originally developed to predict the occurrence of a hemodynamic response (defined as more than 20% increase of heart rate and/or blood pressure) under general anesthesia. However, our technology also proved her reliability on conscious patients before anesthesia , in intensive care units or in the recovery room. The predictive ability of the ANI has been demonstrated by several international studies that have shown that the ANI is significantly decreased within 5 minutes before the onset of hemodynamic reaction (Boselli et al, Minerva Anestesiol, 2015).
The results of the publications concluded today that:
- For an unconscious patient (e.g. under general anesthesia), the target values are between 50 and 70. An ANI below 50 corresponds to an opioids failure and is predictive of hemodynamic response while an ANI higher than 70 encourages to conclude an opioid overdose.
- For the conscious patient, ANI reflects acute pain and the patient’ stress level. The target values are between 50 and 100; an ANI value that approaches 100 reflects an optimized patient’s comfort.
From ECG to ANI: heart rate variability computation
The analysis of the heart rate variability is a well-known method for evaluating the regulation of the cardiovascular system by the autonomic nervous system. Heart rate “short-term” fluctuations reflect the activity of the sympathetic and parasympathetic nervous systems..
The heart rate regulation by the autonomic nervous system is influenced by respiration. Inspiration temporarily inhibits the influence of the parasympathetic nervous system and produces an acceleration of the heart rate. In contrast, the expiration stimulates the parasympathetic nervous system and induces a slowing of heart rate. These rhythmic oscillations produced by breathing are called respiratory sinus arrhythmia. (cf Parasympathetic loop)
Apart from any external influence, the heart has its own rhythm, very regular, instilled by its natural pacemaker, the sinus node. But the sinus node, located in the right atrial tissue is connected to the autonomic nervous system (ANS) by its sympathetic branch (accelerator process) and the parasympathetic branch (moderator process). It is these ANS actions that induce heart rate modulations. The mathematical analysis of these instantaneous variations gives us a picture of the ANS’ activity.
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