The validity and applications of the analgesia nociception index: a narrative review

Abstract

Pain refers to the subjective, unpleasant experience that is related to illness or injury. In contrast to pain, nociception refers to the physiological neural processing of noxious stimuli, such as intra-operative surgical stimuli. One novel device, the Analgesia Nociception Index (ANI), aims to objectively measure intra-operative nociception by analyzing the heart rate variability in patients undergoing surgery. Through this method of nociceptive monitoring, the ANI device aims to provide an objective, continuous evaluation of patient comfort levels and allow anesthesiologists to better manage surgical stress and patient analgesia, perhaps with even better efficacy than current practices used to assess nociception. Additionally, ANI may have clinical application in settings outside of the operating room, such as in the intensive care unit. In this narrative review, we compiled and summarized the findings of many studies that have investigated ANI's validity and applications in different clinical settings. Currently, the literature appears mostly supportive of ANI's ability to detect nociception in both surgical and non-surgical settings. However, the ability for ANI to provide clinical benefits, such as decreased intra-operative opioid use, post-operative opioid use, and post-operative pain compared to standard practices appear controversial. Because of the wide variety of methodology, clinical settings, patient populations, and limitations in these studies, more investigation of ANI is needed before any firm conclusions can be drawn on its clinical benefits.

The Performance of Using the Parasympathetic Tone Activity (PTA) Index to Assess Intraoperative Nociception in Cats

“…In our study, sympathetic nervous system activation (PTAi < 50) was not always accompanied by a clinically significant increase in HR (>20%), i.e., the need for rescue analgesia. This aligns with the findings in human reports [ 5 ]. According to a study conducted on children, the primary benefit of a nociceptive monitor is to optimize opioid titration to prevent overdosage and underdosing, which can lead to opioid-induced hyperalgesia or postoperative pain, respectively [ 6 ].…”

“…The main findings of the current study carried out in a clinical setting in cats undergoing elective OV suggest that the PTA monitor, when using a cut-off value of PTAi < 50 for nociception, demonstrated superior effectiveness in detecting sympathetic nervous system activation/nociception when compared to HR, which is in line with the results of studies carried out in dogs and pigs [ 12 , 19 , 24 ] and humans [ 5 ]. PTA monitoring detected 106 (63.9%) of SS that corresponded to sympathetic nervous system activation, and the HR only detected 23 (13.9%) SS.…”

“…The Analgesia Nociception Index (ANI) is a new monitor utilized in human medicine to quantify the balance between nociception and antinociception [ 5 , 11 , 15 , 16 ], while in veterinary medicine, Parasympathetic Tone Activity (PTA) serves a similar purpose [ 17 , 18 , 19 ]. The PTA signal is acquired in real time using a lead II electrocardiogram (ECG) [ 18 ].…”

Predicting the optimal concentration of remifentanil for skull pin fixation with hemodynamic and analgesia nociception index monitoring

“…ANI decreased with airway manipulation, skin incision and increased with fentanyl administration 26 . However, the use of ANI to provide clinical benefits, such as decreased intraoperative opioid use, postoperative opioid use, and postoperative pain compared to standard practices appeared controversial 27 . In the review, ANI-guided intraoperative opioid consumption might vary based on the type and length of the surgery associated with nociceptive stimuli, the pharmacological properties of the different anesthetics (such as propofol versus inhalation, or continuous infusion of opioid such as remifentanil versus bolus of fentanyl), and sample sizes 27 .…”

Hypnotic Modulation of Autonomic Nervous System (ANS) Activity

“…Recent research indicates that ANI has the capability to not only evaluate parasympathetic alterations associated with nociception and analgesia but also to monitor emotional states in conscious patients and healthy individuals during hypnosis. This emerging evidence highlights the potential of ANI as a versatile tool for assessing various physiological and psychological responses [ 10 , 18 , 19 , 20 , 21 ]. While preliminary evidence suggests a potential link between ANI and vagal activity, definitive conclusions are premature.…”