ANI Monitor V2 - Continuous analgesia monitoring system
MD/PRD/IN16.ANIV2 v.07 - 12 MAR 2020
P a g e
11 | 45
2
ANI Monitor V2
ANI (Analgesia Nociception Index) is a standardized continuous measurement of the relative
pΣ tone (parasympathetic tone). Each respiratory cycle (spontaneous and artificial) induces a
fast, temporary decrease of the pΣ tone, which accounts for Respiratory Sinus Arrhythmia,
and leads to a transient shortening of the R-R intervals (increased heart rate). ANI quantifies
these "respiratory patterns" in order to measure the "relativ
e quantity" of pΣ tone.
The series of normal, non-ectopic, R-R intervals is displayed on the screen of the ANI Monitor
V2
after normalization, resampling and filtering. The amount of pΣ tone is measured in
relation to the total window surface through the area comprised between the lower and the
upper envelope of the RR series, which is continuously displayed as a shaded area. The
higher the pΣ, the higher the shaded surface, and reciprocally.
The ANI is expressed between 0 and 100. Each ANI value is computed on one time window
of 64 sec. This number shows the relative pΣ activity as a part of ANS activity: it expresses
the relative amount of pΣ tone present as compared to sum of sympathetic and pΣ activities.
ANI Monitor V2 displays two averaged ANI measurements: ANIi results from the average of
ANI measured over the previous 120 sec, and ANIm results from the average of ANI
measured over the previous 240 sec.
There are multiple ways of interpreting an ANI value: one is probabilistic, as this index has
been developed in order to predict hemodynamic reactivity during nociceptive stimulation.
When surgical stimulation was constant, all hemodynamic reactivity episodes (20% increase
of heart rate or systolic blood pressure compared to a reference) were associated with a
decreased ANI up to 10 min beforehand. The predictive thresholds need yet to be
established, but preliminary studies suggest:
•
that an ANIm measure between 50 and 70 during surgery makes a hemodynamic
reactivity episode unlikely in the following 10 minutes;
•
that an ANIm lower than 50 makes hemodynamic reactivity very likely in the following
10 minutes.
ANI calculation is based on R-R interval variability in ECG. Since the ANI Monitor V2 is not
an ECG or a cardiac monitor, the electrodes have been designed to retrieve information
related to QRS complexes. The acquisition of a cardiac vector is enough to get an ANI
calculation.
