Monitoring heart rate variability to assess experimentally induced pain using the analgesia nociception index: A randomised volunteer study

High frequency variability index in predicting postoperative pain in video/robotic-assisted thoracoscopic surgery under combined general anesthesia and peripheral nerve block: an observational study

The high frequency variability index (HFVI)/analgesia nociception index (ANI) is purported to assess the balance between nociception and analgesia in patients under general anesthesia. This observational study investigated whether intraoperative HFVI/ANI correlates with postoperative pain in patients performed with nerve block under general anesthesia in video/robotic-assisted thoracoscopic surgery (VATS/RATS). We investigated whether maximum postoperative pain at rest and postoperative morphine consumption are associated with HFVI/ANI just before extubation, mean HFVI/ANI during anesthesia, the difference in HFVI/ANI between before and 5 min after the start of surgery, and the difference in HFVI/ANI between before and 5 min after the nerve block. Data obtained from 48 patients were analyzed. We found no significant association between HFVI/ANI just before extubation and postoperative Numerical Rating Scale (NRS) score. Receiver operating characteristic curve analysis revealed that moderate (NRS > 3) or severe (NRS > 7) postoperative pain could not be predicted by HFVI/ANI just before extubation. In addition, there were no associations between postoperative morphine consumption and HFVI/ANI at any time points. The present study demonstrated that it is difficult to predict the degree of postoperative pain in patients undergoing VATS/RATS under general anesthesia combined with peripheral nerve block, by using HFVI/ANI obtained at multiple time points during general anesthesia.

Assessing pain in paralyzed critically ill patients receiving neuromuscular blocking agents: A monocenter prospective cohort

INTRODUCTION

Given the absence of established recommendations for pain assessment in pharmacologically paralyzed Intensive-Care-Units (ICU) patients under Neuro-Muscular-Blocking Agents (NMBA), this study assessed the validity of various parameters for evaluating pain in this specific population.

PATIENTS AND METHODS

Four electrophysiological parameters (instant-Analgesia-Nociception-Index (ANI), Bispectral index (BIS), Heart Rate (HR) and Mean Arterial Blood Pressure (ABP)) and one clinical parameter (Behavioural-Pain-Scale (BPS)) were recorded during tracheal-suctioning in all consecutive ICU patients who required a continuous infusion of cisatracurium, before and just after paralysis recovery measured by Train-of-Four ratio. The validity of the five pain-related parameters was assessed by comparing the values recorded during different situations (before/during/after the nociceptive procedure) (discriminant-validity, primary outcome), and the effect of paralysis was assessed by comparing values obtained during and after paralysis (reliability, secondary outcome).

RESULTS

Twenty patients were analyzed. ANI, BIS, and HR significantly changed during the nociceptive procedure in both paralysis and recovery, while BPS changed only post-recovery. ANI and HR were unaffected by paralysis, unlike BIS and BPS (mixed-effect model). ANI exhibited the highest discriminant-validity, with values (min 0/max 100) decreasing from 71 [48-89] at rest to 41 [25-72] during tracheal suctioning in paralyzed patients, and from 71 [53-85] at rest to 40 [31-52] in non-paralyzed patients.

CONCLUSIONS

ANI proves the most discriminant parameter for pain detection in both paralyzed and non-paralyzed sedated ICU patients. Its significant and clinically relevant decrease during tracheal suctioning remains unaltered by NMBA use. Pending further studies on analgesia protocols based on ANI, it could be used to assess pain during nociceptive procedures in ICU patients receiving NMBA.

Current perioperative nociception monitoring and potential directions

Perioperative nociception-antinociception balance is essential for the prevention of adverse postoperative events. Estimating the nociception level helps optimize intraoperative management. In the past two decades, various nociception monitoring devices have been developed for the identification of intraoperative nociception. However, each type of nociception monitoring device has advantages and disadvantages, limiting their clinical application in particular patients and settings. Therefore, this review aimed to summarize the information on nociceptor monitoring in current clinical settings, explore each technique's particularities, and possible future directions to provide a reference for clinicians and researchers.

Can Opioid-Free Anaesthesia Be Personalised? A Narrative Review

Background: A significant amount of evidence suggests that Opioid-Free Anaesthesia (OFA) may provide better outcomes for patients undergoing surgery, sparing patients who are particularly vulnerable to adverse side effects of opioids. However, to what extent personalizing OFA is feasible and beneficial has not been adequately described. Methods: We conducted a narrative literature review aiming to provide a comprehensive understanding of nociception and pain and its context within the field of OFA. Physiological (including monitoring), pharmacological, procedural (type of surgery), genetical and phenotypical (including patients’ conditions) were considered. Results: We did not find any monitoring robustly associated with improved outcomes. However, we found evidence supporting particular OFA indications, such as bariatric and cancer surgery. We found that vulnerable patients may benefit more from OFA, with an interesting field of research in patients suffering from vascular disease. We found a variety of techniques and medications making it impossible to consider OFA as a single technique. Our findings suggest that a vast field of research remains unexplored. In particular, a deeper understanding of nociception with an interest in its genetic and acquired contributors would be an excellent starting point paving the way for personalised OFA. Conclusion: Recent developments in OFA may present a more holistic approach, challenging the use of opioids. Understanding better nociception, given the variety of OFA techniques, may help to maximize their potential in different contexts and potential indications.

Analgesia nociception index and high frequency variability index: promising indicators of relative parasympathetic tone

At present, there is no objective and absolute measure of nociception, although various monitoring techniques have been developed. One such technique is the Analgesia Nociception Index (ANI), which is calculated from heart rate variability that reflects the relative parasympathetic tone. ANI is expressed on a non-unit scale of 0-100 (100 indicates maximal relative parasympathetic tone). Several studies indicated that ANI-guided anesthesia may help reduce intraoperative opioid use. The usefulness of ANI in the intensive care unit (ICU) and during surgery has also been reported. However, some limitations of ANI have also been reported; for example, ANI is affected by emotions and some drugs. In 2022, a high frequency variability index (HFVI), which was renamed from ANI and uses the same algorithm as ANI, was commercialized; therefore, ANI/HFVI are currently in the spotlight. Unlike ANI, HFVI can be displayed along with other biometric information on the Root® monitor. ANI/HFVI monitoring may affect the prognosis of not only patients in the perioperative period but those in ICU, those who receive home medical care, or outpatients. In this article, we present an updated review on ANI that has been published in the last decade, introduce HFVI, and discuss the outlooks of ANI/HFVI.

A Forehead Wearable Sensor for the Objective Measurement of Chronic Pain

Chronic pain impacts one in five Americans and is difficult to manage, costing ~USD 600 billion annually. The subjective experience of pain is a complex processing of central nervous system input. Recent advances in magnetic resonance imaging revealed the prefrontal cortex as vital to the perception of pain and that changes in the cerebral hemodynamics can be used to detect painful sensations. Current pain monitoring is dependent on the subjective rating provided by patients and is limited to a single time point. We have developed a biomarker for the objective, real-time and continuous chronic pain assessment using proprietary algorithms termed ROPA and cerebral optical spectrometry. Using a forehead sensor, the cerebral optical spectrometry data were collected in two clinical sites from 41 patients (19 and 22, respectively, from sites 1 and 2), who elected to receive an epidural steroid injection for the treatment of chronic pain. Patients rated their pain on a numeric rating scale, ranging from 0-10, which were used to validate the ROPA objective pain scoring. Multiple time points, including pre- and post-procedure were recorded. The steroid injection was performed per standard medical practice. There was a significant correlation between the patient's reported numeric rating scale and ROPA, for both clinical sites (Overall ~0.81). Holding the subjective pain ratings on a numeric rating scale as ground truth, we determined that the area under the receiver operator curves for both sites revealed at least good (AUC: 64%) to excellent (AUC > 98%) distinctions between clinically meaningful pain severity differentiations (no/mild/moderate/severe). The objective measure of chronic pain (ROPA) determined using cerebral optical spectrometry significantly correlated with the subjective pain scores reported by the subjects. This technology may provide a useful method of detection for the objective and continuous monitoring and treatment of patients with chronic pain, particularly in clinical circumstances where direct assessment is not available, or to complement the patient-reported pain scores.

Effect of music intervention on subjective scores, heart rate variability, and prefrontal hemodynamics in patients with chronic pain

INTRODUCTION

Music interventions have been proposed in recent years as a treatment for chronic pain. However, the mechanisms by which music relieves pain are unclear, and the effects of music intervention on physiological indicators in patients with chronic pain remain to be explored. This study aimed to explore whether a music intervention would have effects on subjective pain ratings, heart rate variability, and functional connectivity of the cerebral cortex in patients with chronic pain.

METHODS

A randomized controlled study was conducted on 37 pain patients aged 18-65 years, with the control group receiving usual care, and the intervention group receiving music intervention (8-150 Hz, 50-70 dB) for 30 min before bedtime for 7 days on top of usual care. Pain visual analog scale and heart rate variability were used as subjective and objective physiological indices before and after the music intervention, respectively. Changes in oxyhemoglobin and deoxyhemoglobin concentrations in the cerebral cortex were measured by functional near-infrared spectroscopy, and whole-brain correlation analysis was used to quantify the connectivity of prefrontal brain regions associated with the pain response.

RESULTS

Results showed that patients with chronic pain in the intervention group had significantly lower visual assessment scale scores, as well as significantly lower overall voluntary mobility during pain episodes, resulting in relatively higher vagal innervation compared to the control group. In addition, connections between the bilateral dorsolateral prefrontal cortex (BA9, BA46) and frontal areas (BA10) were significantly higher in the intervention group.

DISCUSSION

This study demonstrates the effectiveness of the combined application of music interventions with usual care in reducing pain levels in patients with chronic pain and provides insight into the pathological mechanisms of music interventions for analgesia, providing direction for new baseline indicators for quantitative clinical assessment of pain. The study was registered in the Chinese Clinical Trial Registry (No. ChiCTR2100052993).

CLINICAL TRIAL REGISTRATION

[https://www.chictr.org.cn/showproj.aspx?proj=136268], identifier [ChiCTR2100052993].

Heart Rate Variability as a Potential Indicator of Cancer Pain in a Mouse Model of Peritoneal Metastasis

Heart rate variability (HRV) is closely related to changes in the autonomic nervous system (ANS) associated with stress and pain. In this study, we investigated whether HRV could be used to assess cancer pain in mice with peritoneal metastases. At 12 days after cancer induction, positive indicators of pain such as physiological characteristics, appearance, posture, and activity were observed, and time- and frequency-domain HRV parameters such as mean R-R interval, square root of the mean squared differences of successive R-R intervals, and percentage of successive R-R interval differences greater than 5 ms, low frequency (LF), high frequency (HF), and ratio of LF and HF power, were found to be significantly decreased. These parameters returned to normal after analgesic administration. Our results indicate that overall ANS activity was decreased by cancer pain and that HRV could be a useful tool for assessing pain.

Comparison between Analgesia Nociception Index (ANI) and self-reported measures for diagnosing pain in conscious individuals: a systematic review and meta-analysis

The Analgesia Nociception Index (ANI), an objective measure of pain based on heart rate variability (HRV), has its usefulness in awake patients still unclear. This systematic review and meta-analysis aimed to assess ANI's accuracy compared to self-reported pain measures in conscious individuals undergoing medical procedures or painful stimuli. PubMed, Ovid, Web of Science, Scopus, Embase, and grey literature were searched until March 2021. Of the 832 identified citations, 16 studies complied with the eligibility criteria. A meta-analysis including nine studies demonstrated a weak negative correlation between ANI and NRS for pain assessment in individuals in the post-anesthetic recovery room (r = − 0.0984, 95% CI = − 0.397 to 0.220, I² = 95.82%), or in those submitted to electrical stimulus (r = − 0.089; 95% CI = − 0.390 to 0.228, I² = 0%). The evidence to use ANI in conscious individuals is weak compared to self-report measures of pain, yet ANI explains a part of self-report. Therefore, some individuals may be benefited from the use of ANI during procedures or in the immediate postoperative period.

Heart Rate Variability and Pain: A Systematic Review

Background and Objective: Heart rate variability (HRV) as an index of the autonomic nervous system appears to be related to reactivity to experimental pain stimuli. HRV could better explain the contributions of sympathetic and parasympathetic activity response to nociceptive stimulation. The aim of this study was to systematically review and synthesize the current evidence on HRV in relation to the experience of pain in experimental tasks. Databases and Data Treatment: Studies indexed in the PubMed, PsycINFO, MEDLINE, WebOfScience, and Scopus databases were reviewed for eligibility. Studies on the autonomic response (i.e., HRV) to experimentally induced pain in healthy adults were included. Different methods of pain induction were considered (e.g., thermal, pressure, and electrical). Data were synthesized considering the association between HRV and both pain induction and subjective measures of pain. Results: Seventy-one studies were included. The results underline significant change in both the sympathetic and parasympathetic autonomic nervous systems during the painful stimulation independent of the pain induction method. The autonomic reaction to pain could be affected by several factors, such as sex, age, body mass index, breathing patterns, the intensity of the stimulation, and the affective state. Moreover, an association between the autonomic nervous system and the subjective experience of pain was found. Higher parasympathetic activity was associated with better self-regulation capacities and, accordingly, a higher pain inhibition capacity. Conclusions: HRV appears to be a helpful marker to evaluate nociceptive response in experimentally induced pain. Future studies are also needed in clinical samples to understand better the interindividual changes of autonomic response due to pain stimuli.

Elevated Heart Rate and Pain During a Cold Pressor Test Correlates to Pain Catastrophizing

To understand the variable response to pain, researchers have examined the change in cardiovascular measures to a uniform painful stimulation. Pain catastrophizing is the tendency to magnify or exaggerate pain sensations, and it affects the outcome of rehabilitation in a clinical setting. Its effect on cardiovascular changes during a painful stimulus is unclear. Twenty-four healthy human participants completed the study. All participants completed a cold pressor test while subjective pain intensity was measured with a numeric pain scale from 0-10. Continuous cardiac output measurements were obtained with finger-pulse plethysmograph waveform analysis. The measurements included systolic and diastolic blood pressure, heart rate averaged over 30 s intervals. Pain catastrophizing and anxiety were assessed using the pain catastrophizing scale (PCS), and Spielberger's State-Trait Anxiety Inventories, respectively. Peak pain was correlated to pain catastrophizing (r = 0.628, p < 0.01). There was a strong correlation between change in heart rate (HR) and subjective peak pain (r = 0.805, p < 0.01), total PCS (r = 0.474, p < 0.05), and the helplessness subscale of the PCS (r = 0.457, p < 0.05). Peak pain and catastrophizing explained a significant amount of the variance for the change in HR during the cold pressor test (R² of 0.649 and 0.224 respectively, p = 0.019). These novel findings demonstrate a psycho-physiological relationship between cardiovascular changes and pain catastrophizing. Further research should include participants with subacute or persistent pain.

[Nociception monitoring : Method for intraoperative opioid control?]

The intraoperative dosing of opioids is a challenge in routine anesthesia as the potential effects of intraoperative overdosing and underdosing are not completely understood. In recent years an increasing number of monitors were approved, which were developed for the detection of intraoperative nociception and therefore should enable a better control of opioid titration. The nociception monitoring devices use either continuous hemodynamic, galvanic or thermal biosignals reflecting the balance between parasympathetic and sympathetic activity, measure the pupil dilatation reflex or the nociceptive flexor reflex as a reflexive response to application of standardized nociceptive stimulation. This review article presents the currently available nociception monitors. Most of these monitoring devices detect nociceptive stimulations with higher sensitivity and specificity than changes in heart rate, blood pressure or sedation depth monitoring devices. There are only few studies on the effect of opioid titration guided by nociception monitoring and the possible postoperative benefits of these devices. All nociception monitoring techniques are subject to specific limitations either due to perioperative confounders (e.g. hypovolemia) or special accompanying medical conditions (e.g. muscle relaxation). There is an ongoing discussion about the clinical relevance of nociceptive stimulation in general anesthesia and the effect on patient outcome. Initial results for individual monitor systems show a reduction in opioid consumption and in postoperative pain level. Nevertheless, current evidence does not enable the routine use of nociception monitoring devices to be recommended as a clear beneficial effect on long-term outcome has not yet been proven.

Multiparametric Monitoring of Hypnosis and Nociception-Antinociception Balance during General Anesthesia-A New Era in Patient Safety Standards and Healthcare Management

The development of general anesthesia techniques and anesthetic substances has opened new horizons for the expansion and improvement of surgical techniques. Nevertheless, more complex surgical procedures have brought a higher complexity and longer duration for general anesthesia, which has led to a series of adverse events such as hemodynamic instability, under- or overdosage of anesthetic drugs, and an increased number of post-anesthetic events. In order to adapt the anesthesia according to the particularities of each patient, the multimodal monitoring of these patients is highly recommended. Classically, general anesthesia monitoring consists of the analysis of vital functions and gas exchange. Multimodal monitoring refers to the concomitant monitoring of the degree of hypnosis and the nociceptive-antinociceptive balance. By titrating anesthetic drugs according to these parameters, clinical benefits can be obtained, such as hemodynamic stabilization, the reduction of awakening times, and the reduction of postoperative complications. Another important aspect is the impact on the status of inflammation and the redox balance. By minimizing inflammatory and oxidative impact, a faster recovery can be achieved that increases patient safety. The purpose of this literature review is to present the most modern multimodal monitoring techniques to discuss the particularities of each technique.

Can postoperative pain be predicted? New parameter: analgesia nociception index

Background/aim

The Analgesia Nociception Index (ANI) is a new method of identifying nociception-analgesia balance. In this study, we investigate the correlation between the ANI and numeric rating scale (NRS) values immediately before and after extubation. The NRS values were recorded in the postanesthesia care unit, in a group of patients who underwent laparoscopic cholecystectomy, with the aim of evaluating the potential use of ANI values in the prediction of postoperative pain levels.

Materials and methods

The ANI and NRS values, heartbeat rate (HR), systolic and diastolic arterial pressure (SAP/DAP), and oxygen saturation (SpO2) values of the patients were recorded into three groups based on the initial NRS values recorded in the postanesthesia care unit (group I: NRS ≤ 3, group II: NRS 4–6, group III: NRS ≥ 7). Patients whose ANI values were lower than 47, considered as the pain threshold, and the groups to which these patients belonged were also recorded.

Results

Statistically significant increases were noted in HR, SAP, and DAP after extubation, while there was no significant change in ANI values. A weak correlation was identified between the ANI and NRS values of all patient groups.

Conclusion

We failed to identify a correlation between ANI and NRS values before and after extubation. Previous studies suggested that the ANI provides more valuable information in anesthetized patients, whereas our findings show that it is ineffective in the prediction of potential postoperative pain.

Intraoperative nociception-antinociception monitors: A review from the veterinary perspective

OBJECTIVE

To review monitors currently available for the assessment of nociception-antinociception in veterinary medicine.

DATABASES USED

PubMed, Web of Science and Google Scholar. The results were initially filtered manually based on the title and the abstract.

CONCLUSIONS

The provision of adequate antinociception is difficult to achieve in veterinary anaesthesia. Currently, heart rate and arterial blood pressure are used to monitor the response to a noxious stimulus during anaesthesia, with minimum alveolar concentration-sparing effect and stress-related hormones used for this purpose in research studies. However, since none of these variables truly assess intraoperative nociception, several alternative monitoring devices have been developed for use in humans. These nociceptive-antinociceptive monitoring systems derive information from variables, such as electroencephalography, parasympathetic nervous system (PNS) response, sympathetic nervous system response and electromyography. Several of these monitoring systems have been investigated in veterinary medicine, although few have been used to assess intraoperative nociception in animals. There is controversy regarding their effectiveness and clinical use in animals. A nociceptive-antinociceptive monitoring system based on the PNS response has been developed for use in cats, dogs and horses. It uses the parasympathetic tone activity index, which is believed to detect inadequate intraoperative nociception-antinociception balance in veterinary anaesthesia. Nonetheless, there are limited published studies to date, and cardiovascular variables remain the gold standard. Consequently, further studies in this area are warranted.

Continuous Pain Intensity Estimation from Autonomic Signals with Recurrent Neural Networks

Pain is usually measured by patient's self-report, which requires patient collaboration. Hence, the development of an objective automatic pain detection method would be useful in many clinical applications and patient populations. Previous studies have explored the feasibility of using physiological autonomic signals to detect the presence of pain. In this study, we focused on continuously estimating experimental heat pain intensity with high temporal resolution from autonomic signals. Specifically, we employed skin conductance deconvolution and point process heart rate variability analysis to continuously evaluate time-varying autonomic parameters, and presented a regression algorithm based on recurrent neural networks.

Evaluation of Surgical Pleth Index and Analgesia Nociception Index as surrogate pain measures in conscious postoperative patients: an observational study

We evaluated the performance of the Surgical Plethysmographic Index (SPI) and the Analgesia Nociception Index (ANI) as surrogate pain measures and determined their respective cut-off values for detecting pain in conscious postoperative patients. In total, 192 patients after elective surgery were enrolled. Baseline SPI and ANI data were acquired for 10 min in the operating room prior to surgery when the patients rated their pain as 0 on the numerical rating scale (NRS). Upon arrival in the post-anaesthesia care unit (PACU) after surgery, SPI and ANI data were recorded for 10 min. The means of the recorded data at OR and PACU were defined as the values representing baseline and postoperative pain, respectively. SPI and ANI data obtained from 189 patients were analysed, who were anesthetized with propofol (n = 149) or sevoflurane (n = 40). Remifentanil was continuously infused intraoperatively in all patients. The values of SPI and ANI were significantly different in conscious patients without (NRS = 0) and with pain (NRS > 0). The areas under the receiver operating curves for SPI and ANI were 0.73 (P < 0.0001) and 0.67 (P < 0.0001), respectively. The cut-off values for SPI and ANI in predicting postoperative pain were 44 (sensitivity: 84%, specificity: 53%) and 63 (sensitivity: 52%, specificity: 82%), respectively, which are different from those suggested by their respective manufacturers for use in intraoperative state under general anaesthesia. The cut-off values of SPI and ANI for detecting pain were similar regardless of the type of anesthesia.

Effectiveness of the Analgesia Nociception Index Monitoring in Patients Who Undergo Colonoscopy with Sedo-Analgesia

Objective

The objective of this study was to improve the patient comfort and safety during procedures done under anaesthesia and sedation. The analgesia nociception index (ANI) noninvasively provides information on the nociception-antinociception balance, and it can be used to assess analgesia objectively. We aimed to compare the effects of analgesia management with conventional methods and with ANI monitoring on total opioid consumption, sedation and analgesia levels in patients who underwent colonoscopy using sedo-analgesia.

Methods

Adult patients (n=102), scheduled for procedural sedation, were prospectively analysed. After the induction with propofol and ketamine, infusions of propofol (2 mg kg⁻¹ h⁻¹) and remifentanil (0.05 mcg kg⁻¹ min⁻¹) were started. In Group A, remifentanil infusions were titrated to maintain the ANI value between 50 and 70, whereas in Group C, analgesic requirements were met according to the attending anaesthetist’s intention. The heart rate, blood pressure, respiratory rate, SpO₂, BIS, Numeric Rating Scale (NRS) and Ramsay Sedation Scale were monitored. Complications, analgesics consumption, duration of the procedure, demographic information, NRS and the Modified Aldrete Score were evaluated.

Results

A total remifentanil amount used in Group A was 66.51±47.87 mcg and 90.15±58.17 mcg in Group C (p=0.011); there was no difference in total amounts of ketamine and propofol given. There was a negative correlation between ANI and NRS scores of Group A patients at Minute 0 at the level of 0.402, which was significant statistically (p=0.003).

Conclusion

Opioid consumption was diminished when ANI monitoring was used, and thus the patient safety was improved. Further studies with longer procedure times and with a greater number of patients are required to demonstrate whether there is a difference in side effects and recovery times.

Objective monitoring of nociception: a review of current commercial solutions

Nociception, in contrast to pain, is not a subjective feeling, but the physiological encoding and processing of nociceptive stimuli. However, monitoring nociception remains a challenge in attempts to lower the incidence of acute postoperative pain and the move towards a more automated approach to analgesia and anaesthesia. To date, several commercialised devices promise a more accurate reflection of nociception than the traditionally used vital signs, blood pressure and heart rate. This narrative review presents an overview of existing technologies and commercially available devices, and offers a perspective for future research. Although firm conclusions about individual methods may be premature, none currently appears to offer a sufficiently broad applicability. Furthermore, there is currently no firm evidence for any clinically relevant influence of such devices on patient outcome. However, the available monitors have significantly aided the understanding of underlying mechanisms and identification of potential pitfalls.

Analgesia nociception index for the assessment of pain in critically ill patients: a diagnostic accuracy study

Background

Behavioural pain tools are used in Intensive Care Unit (ICU) patients unable to self-report their pain-intensity but need sustained efforts to educate and train the ICU team because of the subjective nature of these clinical tools. This study measured the validity and performance of an electrophysiological monitoring tool based on the spectral analysis of heart rate variability, the Analgesia Nociception Index (ANI) which varies from 0 (minimal parasympathetic tone, maximal stress-response and pain) to 100 (maximal parasympathetic tone, minimal stress-response and pain).

Methods

Mean-ANI (ANIm) and Instant-ANI (ANIi) were continuously recorded then compared with the Behavioral Pain Scale (BPS) before, during and after routine care procedures in critically-ill non-comatose patients.

Results

969 assessments were performed in 110 patients. ANIi was the most discriminative pain tool. It was significantly correlated with BPS (r=-0.30; 95%CI -0.37 to -0.25; P<0.001). For an ANIi threshold of 42.5, the sensitivity, specificity, positive and negative predictive values were respectively 61.4%, 77.4%, 37.0%, and 90.4%. Compared with the BPS, ANIi had no significantly different ability to change during turning and tracheal-suctioning but changed significantly more during dressing change. ANIi increased independently with age, obesity and severity of illness, and controlled mechanical-ventilation, vasopressors use and analgesia. ANIi decreased independently when vigilance status and respiratory rate increased. ANIm demonstrated poor psychometric properties to detect pain.

Conclusions

Despite low sensitivity/specificity, ANIi≥43 had a Negative-Predictive-Value of 90%. Hence ANIi may be of highest benefit for excluding significant pain. A randomized controlled trial should compare sedation-analgesia protocols based on ANIi to presently recommended behavioural-pain-tools.

Evaluation of the effects of dexmedetomidine and remifentanil on pain with the analgesia nociception index in the perioperative period in hysteroscopies under general anesthesia. A randomized prospective study

Objectives To compare analgesia nociception index (ANI) values, visual analog scale (VAS) values, and hemodynamic parameters in hysteroscopy patients who received remifentanil and dexmedetomidine during general anesthesia. Methods: In total, 30 patients who underwent hysteroscopy between March and September 2016 at the University of Health Sciences Fatih Sultan Mehmet Health Research and Application Center, Ankara, Turkey were included in this prospective study. Standard hemodynamic monitoring, ANI, and bispectral index (BIS) monitoring were applied to the patients. At 10 min prior to induction, 1 μg/kg of remifentanil was applied in Group R (n=15) and 1 μg/kg of dexmedetomidine was applied in Group D (n=15). After induction, sevoflurane was used for maintenance with dexmedetomidine at 0.2-0.7 μg/kg/hour in Group D and remifentanil at 0.05-0.5 μg/kg/minute in Group R. Perioperative and postoperative analgesia levels (ANI and VAS, respectively), hemodynamics, and complications were recorded. Results: Even though the ANI levels in Group D were lower at the perioperative 5th and 10th minutes, the ANI values were between the targeted limits, except for the measurement after I-gel insertion, in both groups. Hemodynamic parameters were within normal limits, but the mean arterial pressures in Group R after induction, following I-gel placement, and at the perioperative 5th, 10th, and 20th minutes were lower and at postoperative 30th minute were significantly higher.   Conclusion: Dexmedetomidine and remifentanil are both efficacious agents for perioperative analgesia in hysteroscopy cases.

The comparison of effectiveness of two variants of preventive anesthesia/analgesia in cancer surgery

Despite modern drugs and technologies in medicine, the questions of adequate analgesia in the postoperative period remain quite relevant. The effectiveness of preventive analgesia in the perioperative period remains a contentious issue. The study included 53 oncosurgical patients. Gr.1 received dexketoprofen in combination with paracetamol for perioperative analgesia before the operation, Gr.2 the same medication was given before closing the operating wound. Anesthesia in both groups included an inhaled (Sevoran) and an extended epidural. The study showed that the pain intensity on ANI monitoring and the total dose of fentanyl was less in Gr.1, compared to Gr.2. Cortisol plasma level and the level of glycemia in the perioperative period were less in patients in Gr.1 than in Gr.2. Pain intensity after surgery during first postoperative day was lower in Gr.1, then in Gr.2. The administration of multimodal analgesia with paracetamol and dexketoprofen prior to the surgical interventions provides for the best quality of perioperative analgesia in oncological surgical interventions.

Correlation of changes in hemodynamic response as measured by cerebral optical spectrometry with subjective pain ratings in volunteers and patients: a prospective cohort study

Purpose

Noninvasive cerebral optical spectrometry is a promising candidate technology for the objective assessment physiological changes during pain perception. This study’s primary objective was to test if there was a significant correlation between the changes in physiological parameters as measured by a cerebral optical spectrometry-based algorithm (real-time objective pain assessment [ROPA]) and subjective pain ratings obtained from volunteers and laboring women. Secondary aims were performance assessment using linear regression and receiver operating curve (ROC) analysis.

Patients and methods

Prospective cohort study performed in Human Pain Laboratory and Labor and Delivery Unit. After institutional review board approval, we evaluated ROPA in volunteers undergoing the cold pressor test and in laboring women before and after epidural or combined spinal epidural placement. Linear regression was performed to measure correlations. ROCs and corresponding areas under the ROCs (AUC), as well as Youden’s indices, as a measure of diagnostic effectiveness, were calculated.

Results

Correlations between numeric rating scale or visual analog scale and ROPA were significant for both volunteers and laboring women. AUCs for both volunteers and laboring women with numeric rating scale and visual analog scale subjective pain ratings as ground truth revealed at least good (AUC: 70%–79%) to excellent (AUC >90%) distinction between clinically meaningful pain severity differentiations (no/mild–moderate–severe).

Conclusion

Cerebral Optical Spectrometry-based ROPA significantly correlated with subjectively reported pain in volunteers and laboring women, and could be a useful monitor for clinical circumstances where direct assessment is not available, or to complement patient-reported pain scores.

Heart rate variability: implications for perioperative anesthesia care

PURPOSE OF REVIEW

Heart rate variability (HRV) is a measure of the balance between both the parasympathetic and sympathetic nervous system and may provide useful information for anesthesia care providers. HRV may offer predictive information about critically ill and operative patients. Further, HRV collection provides real-time information of patient autonomic nervous system status and may allow tailoring of the analgesia for patients in the ICU and operating room.

RECENT FINDINGS

Reduced and abnormal resting HRV predict sudden and nonsudden cardiac death. Recent evidence shows that decreased HRV correlates with worsened outcomes in both trauma patients and patients with sepsis, as well as the risk of developing hypotension after induction of general anesthesia and placement of intrathecal local anesthesia. In addition, HRV appears to provide an accurate assessment of the nociception-analgesia balance in deeply sedated ICU patients and those under general anesthesia.

SUMMARY

No study has assessed the prognostic value of preoperative HRV in patients presenting for surgery. Use of HRV for patient risk stratification and intraoperative analgesia management may allow tailored perioperative care and improved outcomes. If intraoperative HRV data leads to decreased perioperative opioid use, opioid-related adverse events, a serious perioperative issue, may be decreased.

CLINICAL TRIALS REGISTRATION

Not applicable.

Effects of hypnosis on the relative parasympathetic tone assessed by ANI (Analgesia/Nociception Index) in healthy volunteers: a prospective observational study

Hypnosis has shown an effect on the regulation of the autonomic nervous system by increasing parasympathetic activity. The Analgesia/Nociception Index (ANI) is derived from heart rate variability and represents the relative parasympathetic tone. We investigated the effects of hypnosis on ANI in healthy volunteers. Participants to the 2016 International Hypnosis congress, Saint Malo, France were recruited in this prospective observational study. After comfortable positioning of the subject in the sitting position (T0), the hypnotic trance was induced (T1) then conducted with suggestions of comfort (T2) before return to normal consciousness (T3). The ANI, heart rate (HR) and respiratory rate (RR) were recorded at the different time-points. Forty subjects were enrolled (31 women, 9 men). The mean ± SD ANI at T2 (84 ± 12) was significantly greater than at T0 (60 ± 10), T1 (62 ± 9) and T3 (59 ± 11). The median [25th-75th percentile] ANI values at T2 were significantly greater in women (90 [83-95]) than in men (74 [68-83]). There were no significant variations of HR during time. The median [25th-75th percentile] RR at T1 (16 [14-18] breaths/min) and T2 (14 [12-16] breaths/min) were significantly smaller than at T0 (18 [16-20] breaths/min) and T3 (18 [16-20] breaths/min). This study shows that hypnosis induces an increase in the relative parasympathetic tone assessed by ANI in healthy volunteers, with greater ANI values observed in women. These results suggest that ANI monitoring may provide an objective tool for the measurement of the intensity of the hypnotic process, although this should be confirmed by further studies.

Cerebral oxygenation for pain monitoring in adults is ineffective: A sequence-randomized, sham controlled study in volunteers

BACKGROUND

Pain assessment by Numeric Rating Scale (NRS) is considered to be good clinical practice, but objective pain assessment is still a challenge. Near infrared spectroscopy (NIRS) measures cerebral tissue oxygen saturation (SctO₂) that increases with cortical-neuronal activity and may provide point-of-care bedside pain monitoring. Analogous to promising studies in newborns, we hypothesize that different levels of SctO₂ can probably quantify pain intensity. SctO₂ may increase following painful in contrast to non-painful or sham stimuli and may correlate with pain intensity as assessed by NRS in volunteers.

METHODS

Twenty healthy male students (24.2±1.9 years), recruited via local advertising, were consecutively included in a sequence-randomized, sham-controlled, single-blinded study. SctO₂ was recorded continuously with two NIRS sensors on the forehead. After resting, four stimuli were applied in a random order on the right forearm (unexpected and expected electrical pain, expected non-painful and sham stimuli). Blinded subjects were asked to rate each stimulus on NRS.

STATISTICS

RM-ANOVA; Wilcoxon or paired Student t-test; Spearman's rank correlation; P<.05.

RESULTS

Resting volunteers showed SctO₂ of 72.65%±3.39. SctO₂ significantly increased for about 60 to 70s until a maximum after unexpected painful (74.62%±3.9; P=.022) and sham stimuli (74.07%±3.23; P=.014). Expected painful (P=.139) and non-painful stimuli (P=.455) resulted in no changes in SctO₂. NRS scores (median, IQR) were rated significantly higher after expected (5.25, 3.5 to 6.75) than after unexpected (4.5, 3 to 5; P=.008) pain. No strong correlation was found between NRS and SctO₂.

CONCLUSIONS AND IMPLICATIONS

Contrary to our expectations, measuring SctO₂ via a two-channel NIRS is not able to remediate the lack of objective bedside pain assessment under standardized experimental conditions in alert adults.

TRIAL REGISTRATION

DRKS 00011575 (retrospectively registered).

Evaluation of the Parasympathetic Tone Activity (PTA) index to assess the analgesia/nociception balance in anaesthetised dogs

The Parasympathetic Tone Activity (PTA) is an index based on the analysis of heart rate variability that has been recently developed to assess the analgesia/nociception balance in anaesthetised animals. The present study aimed to evaluate its performance in dogs undergoing surgery. Thirty dogs admitted for elective surgeries, were anaesthetised with a standardised protocol. PTA, heart rate (HR), systolic blood pressure (SBP) and HDR (defined as an increase by >20% in HR and/or SBP within 5min) were assessed at the following predefined time-points: T_StSt (steady-state, after induction of anaesthesia and before start of surgery), T_Clamp (clamping of surgical drapes on the skin), T_Cut (cutaneous incision), T_PrePTA (retrospectively assessed 1min before a PTA decline of at least 20%) and T_EndIso (isoflurane discontinuation). The dynamic variation of PTA over 1min (∆PTA) was calculated at each predefined time-points and its performance to predict HDR was assessed by building Receiver Operating Characteristics (ROC) curves. A significant decrease of PTA (p<0.002) was detected 1min after T_Clamp, T_Cut and T_PrePTA followed by a significant increase in HR and/or SBP within 5min after the time points (p<0.01). The ΔPTA was associated with the following performance in predicting HDR: AUC ROC [95% CI]=0.80 [0.71 to 0.88] (p<0.05), with a sensitivity of 77% and a specificity of 72% for a threshold value of -18%. Although encouraging, the performance of the PTA index and its dynamic variation needs to be further evaluated, particularly in different clinical contexts.

Heart rate variability during treatment of breakthrough pain in patients with advanced cancer: a pilot study

Background

Decisions on the intensity of analgesic therapy and judgments regarding its efficacy are difficult at the end of life, when many patients are not fully conscious and pain is a very common symptom. In healthy individuals and in postoperative settings, nociception and subsequent pain relief have been shown to induce changes in the autonomic nervous system (ANS), which can be detected by measuring heart rate variability (HRV).

Objectives

The changes in the ANS were studied by measuring HRV during opioid therapy for cancer breakthrough pain (CBTP) in palliative-care patients with cancer and compared these changes with patient-reported pain levels on a numeric rating scale (NRS).

Patients and methods

The study included ten patients with advanced cancer and baseline opioid therapy. In each patient, a 24-hour peak-to-peak HRV measurement with a sampling rate of 4,000 Hz was performed. High frequency (HF), low frequency (LF), total power, pNN50 (indicating parasympathetic activity), and log LF/HF were obtained in two intervals prior to therapy and in four intervals thereafter. Intensity of CBTP was recorded using a patient-reported NRS prior to therapy and 30 minutes afterward.

Results

CBTP occurred in seven patients (three males and four females; mean age: 62 ± 5.2 years) and was treated with opioids. A highly significant positive correlation was found between opioid-induced reduction in patient-reported pain intensity based on NRS and changes in log LF/HF (r > 0.700; p < 0.05). Log LF/HF decreased in patients who had a reduction in pain of >2 points on the NRS but remained unchanged in the other patients.

Conclusion

Our data suggest that log LF/HF may be a useful surrogate marker for alleviation of CBTP in patients with advanced cancer and might allow detection of pain without active contribution from patients.

Paracetamol and morphine for infant and neonatal pain; still a long way to go?

INTRODUCTION

Pharmacologic pain management in newborns and infants is often based on limited scientific data. To close the knowledge gap, drug-related research in this population is increasingly supported by the authorities, but remains very challenging. This review summarizes the challenges of analgesic studies in newborns and infants on morphine and paracetamol (acetaminophen). Areas covered: Aspects such as the definition and multimodal character of pain are reflected to newborn infants. Specific problems addressed include defining pharmacodynamic endpoints, performing clinical trials in this population and assessing developmental changes in both pharmacokinetics and pharmacodynamics. Expert commentary: Neonatal and infant pain management research faces two major challenges: lack of clear biomarkers and very heterogeneous pharmacokinetics and pharmacodynamics of analgesics. There is a clear call for integral research addressing the multimodality of pain in this population and further developing population pharmacokinetic models towards physiology-based models.

Heart rate variability and cardiac baroreflex inhibition-derived index predicts pain perception in burn patients

BACKGROUND

Dressing changes induce acute pain in burn patients. This pain is difficult to predict and may be therefore undertreated. Two different non-invasive electrophysiological indices from heart rate variability and baroreflex inhibition-derived indices, analgesia/nociception index (ANI) and cardiovascular depth of analgesia (CARDEAN), have been proposed to predict and better assess adequacy of anti-nociception. The aim of this study was to evaluate these techniques as early pain alert tools in conscious burnt patients during dressing changes' procedures.

METHODS

Twenty adult burnt patients undergoing scheduled wound treatment procedures were included in this prospective observational study. Pain intensity was assessed using a 0-10 numerical rating scale (NRS) and was compared with both ANI and CARDEAN, during the procedures. Non parametric rank sum test and linear discriminant analysis were used for evaluating potential differences of measured variables between periods with different pain intensities. Receiver-operating characteristic (ROC) curves were built to assess their performance to detect pain within following 15s.

RESULTS

The sensitivity and specificity of ANI to detect pain were 67% and 70% and those of CARDEAN were 77% and 80%, with area under the curve (AUC) values of 0.75 and 0.83, respectively. Their combination increased AUC to 0.87.

CONCLUSIONS

Both ANI and CARDEAN indices during wound treatment procedures seem to discriminate periods with and without pain within 15s, serving as a potential complementary tool for early optimized pain control.

Measurement of Heart Rate Variability to Assess Pain in Sedated Critically Ill Patients: A Prospective Observational Study

Introduction

The analgesia nociception index (ANI) assesses the relative parasympathetic tone as a surrogate for antinociception/nociception balance in sedated patients. The aim of this study is to determine the effectiveness of ANI in detecting pain in deeply sedated critically ill patients.

Methods

This prospective observational study was performed in two medical ICUs. All patients receiving invasive mechanical ventilation and deep sedation were eligible. In all patients, heart rate and ANI were continuously recorded using the Physiodoloris^® device during 5 minutes at rest (T1), during a painful stimulus (T2), and during 5 minutes after the end of the painful stimulus (T3). The chosen painful stimulus was patient turning for washstand. Pain was evaluated at T2, using the behavioral pain scale (BPS). The primary objective was to determine the effectiveness of ANI in detecting pain. Secondary objectives included the impact of norepinephrine on the effectiveness of ANI in detecting pain, and the correlation between ANI and BPS.

Results

Forty-one patients were included. ANI was significantly lower at T2 (Med (IQR) 69(55–78)) compared with T1 (85(67–96), p<0.0001), or T3 (81(63–89), p<0.0001). Similar results were found in the subgroups of patients with (n = 21) or without (n = 20) norepinephrine. ANI values were significantly higher in patients with norepinephrine compared with those without norepinephrine at T1, and T2. No significant correlation was found between ANI and BPS at T2.

Conclusions

ANI is effective in detecting pain in deeply sedated critically ill patients, including those patients treated with norepinephrine. No significant correlation was found between ANI and BPS.