Analgesia Nociception Index (ANI) and ephedrine: a dangerous liasion.

The Analgesia Nociception Index is a dimensionless scale derived from the heart rate variability; by analyzing the heart rate variability oscillations, it reflects the activity of the sympathetic and parasympathetic nervous systems and ultimately helps to evaluate the Nociception-Antinociception balance during anesthesia and surgery. Drugs like ephedrine affect the heart rate variability inducing artifacts in the ANI readings which should be taken into account in the clinical practice and in clinical research.