The potential for autonomic neuromodulation to reduce perioperative complications and pain: a systematic review and meta-analysis

Non-invasive vagus nerve stimulation and exercise capacity in healthy volunteers: a randomized trial

BACKGROUND AND AIMS

Vagal parasympathetic dysfunction is strongly associated with impaired exercise tolerance, indicating that coordinated autonomic control is essential for optimizing exercise performance. This study tested the hypothesis that autonomic neuromodulation by non-invasive transcutaneous vagus nerve stimulation (tVNS) can improve exercise capacity in humans.

METHODS

This single-centre, randomized, double-blind, sham-controlled, crossover trial in 28 healthy volunteers evaluated the effect of bilateral transcutaneous stimulation of vagal auricular innervation, applied for 30 min daily for 7 days, on measures of cardiorespiratory fitness (peak oxygen consumption (VO2peak)) during progressive exercise to exhaustion. Secondary endpoints included peak work rate, cardiorespiratory measures, and the whole blood inflammatory response to lipopolysaccharide ex vivo.

RESULTS

tVNS applied for 30 min daily over 7 consecutive days increased VO2peak by 1.04 mL/kg/min (95% CI: .34-1.73; P = .005), compared with no change after sham stimulation (-0.54 mL/kg/min; 95% CI: -1.52 to .45). No carry-over effect was observed following the 2-week washout period. tVNS increased work rate (by 6 W; 95% CI: 2-10; P = .006), heart rate (by 4 bpm; 95% CI: 1-7; P = .011), and respiratory rate (by 4 breaths/min; 95% CI: 2-6; P < .001) at peak exercise. Analysis of the whole blood transcriptomic response to lipopolysaccharide in serial samples obtained from five participants showed that tVNS reduced the inflammatory response.

CONCLUSIONS

Non-invasive vagal stimulation improves measures of cardiorespiratory fitness and attenuates inflammation, offering an inexpensive, safe, and scalable approach to improve exercise capacity.

'Transauricular vagus nerve stimulation' for prevention of postoperative delirium in elderly patients undergoing major surgery: a study protocol for a multicentre, participant-blinded and assessor-blinded, randomised, controlled trial

INTRODUCTION

Postoperative delirium (POD) is a frequent complication in elderly patients undergoing major surgery. Research has shown that neuroinflammation, postoperative pain and autonomic nervous system dysfunction play significant roles in its onset. Vagus nerve stimulation (VNS) has the potential to reduce inflammation, ease postoperative pain and aid in recovery by enhancing acetylcholine release and activating the cholinergic anti-inflammatory pathway. This study aims to assess the effectiveness and safety of transauricular VNS (ta-VNS) in preventing POD in elderly patients undergoing major surgery.

METHODS AND ANALYSIS

This multicentre, participant-blinded and assessor-blinded, randomised, parallel-group controlled trial will compare the incidence of POD in elderly patients undergoing major surgery who receive ta-VNS versus sham stimulation. A total of 300 eligible patients will be randomly assigned in a 1:1 ratio to either the active or sham stimulation group. The active stimulation group will receive electrical stimulation to the left cymba conchae at a frequency of 30 Hz and a pulse width of 250 µs, with a 30 s on/30 s off cycle. The intensity will start at 0.4V and be increased in 0.4V increments until a tingling sensation is felt, then adjusted to the highest tolerable level without pain. After obtaining informed consent and randomisation, the initial intervention will begin in the preoperative area and continue throughout the surgery. For the four postoperative days, the intervention will be administered twice daily in 2-hour sessions each morning and afternoon. The sham group will follow the same procedure, with electrodes placed on the left cymba conchae. After adjusting the stimulation intensity, the device will be switched off. The primary outcome is the incidence of POD from postoperative day 0 to day 7 or discharge. Secondary outcomes include the severity of POD, quality of recovery, sleep quality and adverse events.

ETHICS AND DISSEMINATION

The protocol was approved by Sir Run Run Shaw Hospital Affiliated to Zhejiang University School of Medicine on 9 January 2024 (Approval number: 20240014), and the trial was registered on the Chinese Clinical Trial Registry on 21 February 2024, prior to recruitment. The study will be performed according to the guidelines of the Declaration of Helsinki. Written informed consent will be obtained from all participants. The results will be submitted for publication in a refereed journal.

TRIAL REGISTRATION NUMBER

ChiCTR2400081078.

The autonomous nervous system and the cholinergic anti-inflammatory reflex in postoperative neurocognitive disorders

PURPOSE OF REVIEW

Postoperative delirium (POD) is a common and serious complication after surgery. It is associated with postoperative neurocognitive disorder (PNCD). The vagal cholinergic anti-inflammatory pathway (CAP) has been hypothesized to play a role in POD/PNCD and may be a target for interventions such as transcutaneous auricular stimulation (taVNS). We aim to review associations of heart rate variability (HRV) as an indicator of vagal function with POD and postoperative immune reaction as well as taVNS as a potential preventive intervention for POD.

RECENT FINDINGS

Autonomous nervous system (ANS) dysfunction was a common finding in studies analysing HRV in POD and postoperative cognitive dysfunction, but results were heterogeneous. There was no evidence from HRV analysis that vagal activity prevents overshooting postoperative immune activation, but HRV may help to identify patients at risk for postoperative infections. Animal studies and preliminary trials suggest that taVNS may be used to prevent POD/PNCD.

SUMMARY

Our review provides no evidence that CAP suppression is associated with POD/PNCD. Future studies should consider that high vagal tone may also mediate immunosuppression in surgical patients, yielding an increased risk for postoperative infections. Although taVNS is a promising approach to prevent POD/POCD, future studies should take these concerns into account.

Pain Management Following Total Hip Arthroplasty With Percutaneous Auricular Stimulation (Neuromodulation): A Randomized, Double-Masked, Sham-Controlled Pilot Study

Objectives Percutaneous auricular neuromodulation involves implanting electrodes around the ear and administering an electric current. A device is currently available in the United States, cleared to treat symptoms from opioid withdrawal, with multiple reports suggesting a possible postoperative analgesic effect. This randomized, controlled pilot study aimed to (1) assess the feasibility of a postoperative auricular neuromodulation protocol and (2) provide an estimate of its treatment effects on postoperative pain and opioid consumption following total hip arthroplasty. Methods Adults undergoing unilateral, primary, total hip arthroplasty received an auricular neuromodulation device (NSS-2 BridgeTM, Masimo, Irvine, California) applied following surgery. Participants were randomized to five days of either electrical stimulation or sham in a double-masked fashion and discharged home with their devices in situ. Participants or their caretakers removed the devices at home. Results One participant randomized to active treatment removed the device the morning of postoperative day one and withdrew from the study prior to any data collection. The remaining 29 participants were included in the analysis. For the first primary outcome measure, the median (IQR) pain level in the first five days for those receiving active stimulation (n=14) was 2.5 (1.0, 3.8) versus 3.0 (1.9, 4.0) for the sham group (n=15) (P=0.721). Concurrently, the median oxycodone use for the active stimulation group was 3.5 mg (0.1, 9.5) compared to 9.0 mg (2.0, 15.3) for the sham group (P=0.263). No statistically significant differences between treatments were identified for any of the secondary outcome measures. The protocol was successful regarding participant recruitment, intervention administration, data collection, outcomes assessment, and analysis. Six participants (three from each treatment group) removed their device prior to postoperative day five due to either difficulty sleeping while using the device or pain at one of the electrode sites. Conclusions While this randomized, controlled pilot study demonstrated the feasibility of using percutaneous auricular nerve stimulation following total hip arthroplasty for both the inpatient and outpatient portions of the postoperative period, it failed to identify improvements in analgesia, opioid-sparing, or pain interference in psychological and physical functioning. Therefore, it remains unclear whether a definitive clinical trial is warranted to investigate its use following total hip arthroplasty. Further research is advisable, possibly with a different auricular neuromodulation device and larger sample sizes.

Percutaneous auricular neuromodulation (nerve stimulation) for the treatment of pain following total knee arthroplasty: a randomized, double-masked, sham-controlled pilot study

BACKGROUND

Percutaneous auricular nerve stimulation (neuromodulation) is an analgesic technique involving the percutaneous implantation of multiple leads at various points on/around the ear followed by the delivery of electric current using an external pulse generator. A device is currently available within the USA cleared to treat symptoms from opioid withdrawal, and multiple reports suggest a possible postoperative analgesic effect. The current randomized, controlled pilot study was undertaken to (1) determine the feasibility and optimize the protocol for a subsequent definitive clinical trial and (2) estimate the treatment effect of auricular neuromodulation on postoperative pain and opioid consumption following total knee arthroplasty.

METHODS

Within the recovery room following primary, unilateral, total knee arthroplasty, an auricular neuromodulation device (NSS-2 Bridge, Masimo, Irvine, California, USA) was applied using three percutaneous leads and one ground electrode. Participants were randomized to 5 days of either electrical stimulation or sham stimulation in a double-masked fashion. Participants were discharged with the stimulator in situ and removed the disposable devices at home. The dual primary treatment effect outcome measures were the cumulative opioid use (oral oxycodone) and the mean of the "average" daily pain measured with the Numeric Rating Scale for the first 5 postoperative days.

RESULTS

During the first five postoperative days, oxycodone consumption in participants given active stimulation (n=15) was a median (IQR) of 4 mg (2-12) vs 13 mg (5-23) in patients given sham (n=15) treatment (p=0.039). During this same period, the average pain intensity in patients given active stimulation was a median (IQR) of 2.5 (1.5-3.3) vs 4.0 (3.6-4.8) in those given sham (p=0.014). Awakenings due to pain over all eight postoperative nights in participants given active stimulation was a median (IQR) of 5 (3-8) vs 11 (4-14) in those given sham (p<0.001). No device-related localized cutaneous irritation, systemic side effects, or other adverse events were identified.

CONCLUSIONS

Percutaneous auricular neuromodulation reduced pain scores and opioid requirements during the initial week after total knee arthroplasty. Given the ease of application as well as the lack of systemic side effects and reported complications, a definitive clinical trial appears warranted.

TRIAL REGISTRATION NUMBER

NCT05521516.

Short-term exposure to indoor artificial light at night during sleep impairs cardiac autonomic function of young healthy adults in China

The artificial light at night (ALAN) exposure has emerged as a significant environmental and public health concern globally. However, there is far less evidence on the health effects of indoor ALAN than on outdoor ALAN. Moreover, evidence on cardiovascular effects of indoor ALAN is more limited. To evaluate the association between short-term exposure to ALAN during sleep with heart rate variability (HRV) in young healthy adults, as well as the mediating role of blood oxygen saturation (SpO2), and to further explore the intervention effects of shading habits, this prospective repeated measurement study was conducted among 81 adults with 150 nights (1324h) of HRV monitoring. HRV and SpO2 were monitored during sleep, concurrently with the measurement of indoor and outdoor ALAN. Shading habits were defined as whether to wear blindfolds or draw bed curtains during sleep, and were collected by questionnaires. Linear mixed-effect model was conducted to assess the association between ALAN exposure and HRV indices. The role of SpO2 in the association was analyzed using mediation analyses. We found that indoor ALAN exposure reduced parasympathetic activity and imbalanced cardiac autonomic function. We also found that the use of outdoor ALAN may underestimate or misestimate the potential health effects of ALAN. A significant mediation effects were observed on standard deviation of normal-to-normal intervals (SDNN; p-value for ACME = 0.014) and the ratio of low frequency power to high frequency power (LF/HF; p-value for ACME = 0.026) through minimum SpO2 after indoor ALAN exposure. The association between indoor ALAN and HRV was more pronounced among participants without shading habits during sleep. This study provides general population-based evidence that short-term exposure to indoor ALAN was significantly associated with impaired HRV, and SpO2 partially mediated the association. Improve shading habits during sleep may mitigate the adverse effects of indoor ALAN.

Heart rate deceleration capacity as a marker of perioperative risk: identifying relevant patient phenotypes and surgical procedures

Loss of regulation of the autonomic nervous system is found in many diseases from the age of 50 to 60 yr and even more so in older patients. The imbalance is usually manifested by an increase in sympathetic tone, long considered to be the most deleterious element in terms of cardiac rhythmic risk, but also by a reduction in the effectiveness of short-term regulation of the baroreflex arc (partial loss of parasympathetic control). Techniques for analysing this autonomic disorder by analysing heart rate regulation are widely available in outpatient clinics and provide interesting indicators of cardiovascular and cerebrovascular risk. Deceleration capacity of cardiac autonomic control has been identified for its prognostic role in high-risk patients and in the general population. Further research is indicated to assess the value of this marker in anaesthetic risk management by targeting procedures with greater risk of intraoperative and postoperative autonomic dysfunction.

Acustimulation combined with pharmacological prophylaxis versus pharmacological prophylaxis alone in postoperative nausea and vomiting (PONV) prophylaxis among patients undergoing laparoscopy abdominal surgery: a research protocol for a randomised controlled trial

INTRODUCTION

This study evaluates the efficacy of integrating percutaneous electrical nerve stimulation at the pericardium 6 (PC6) acupuncture point through a wearable acustimulation device with standard pharmacological prophylaxis to prevent postoperative nausea and vomiting (PONV) compared with pharmacological prophylaxis alone in patients undergoing laparoscopic abdominal surgery.

METHOD AND ANALYSIS

This prospective study will enrol 302 patients scheduled for elective laparoscopic surgery. Participants will be randomly allocated to one of two groups: acustimulation combined with pharmacological prophylaxis or sham stimulation combined with pharmacological prophylaxis. Randomisation will involve a computer-generated sequence, with allocation concealment implemented through sealed envelopes. The acustimulation group will receive electrical stimulation at the PC6 point starting 30 min before surgery and continuing until discharge from the postanaesthesia care unit. Sham group will wear a wristband that does not provide stimulation. The primary outcome is the incidence of PONV. Secondary outcomes include the severity of PONV, incidence rates of nausea and vomiting at different postoperative intervals and indices of gastrointestinal functional recovery. Exploratory outcomes will assess haemodynamic parameters, baroreflex sensitivity, hospital stay duration, costs and both short-term and long-term postoperative recovery.

ETHICS AND DISSEMINATION

All participants will provide written informed consent. The study has been approved by the Ethics Committee of Peking Union Medical Hospital (approval number: I-23PJ1712). Results will be published open access.

TRIAL REGISTRATION NUMBER

NCT06241547.

Percutaneous auricular neuromodulation (nerve stimulation) for the treatment of pain following cholecystectomy and hernia repair: a randomized, double-masked, sham-controlled pilot study

BACKGROUND

Percutaneous auricular nerve stimulation (neuromodulation) involves implanting electrodes around the ear and administering an electric current. A device is currently available within the USA cleared to treat symptoms from opioid withdrawal, and multiple reports suggest a possible postoperative analgesic effect. The current randomized controlled pilot study was undertaken to (1) determine the feasibility and optimize the protocol for a subsequent definitive clinical trial; and (2) estimate the treatment effect of auricular neuromodulation on postoperative pain and opioid consumption following two ambulatory surgical procedures.

METHODS

Within the recovery room following cholecystectomy or hernia repair, an auricular neuromodulation device (NSS-2 Bridge, Masimo, Irvine, California, USA) was applied. Participants were randomized to 5 days of either electrical stimulation or sham in a double-blinded fashion.

RESULTS

In the first 5 days, the median (IQR) pain level for active stimulation (n=15) was 0.6 (0.3-2.4) vs 2.6 (1.1-3.7) for the sham group (n=15) (p=0.041). Concurrently, the median oxycodone use for the active stimulation group was 0 mg (0-1), compared with 0 mg (0-3) for the sham group (p=0.524). Regarding the highest pain level experienced over the entire 8-day study period, only one participant (7%) who received active stimulation experienced severe pain, versus seven (47%) in those given sham (p=0.031).

CONCLUSIONS

Percutaneous auricular neuromodulation reduced pain scores but not opioid requirements during the initial week after cholecystectomy and hernia repair. Given the ease of application as well as a lack of systemic side effects and reported complications, a definitive clinical trial appears warranted.

TRIAL REGISTRATION NUMBER

NCT05521516.

Novel ultrasound-guided supraclavicular stellate ganglion block

INTRODUCTION

Stellate ganglion block (SGB) provides diagnostic and therapeutic benefits in pain syndromes in the head, neck, and upper extremity, including complex regional pain syndrome Types I and II, Raynaud's disease, hyperhidrosis, arterial embolism in the region of the arm.

METHODS

We present a novel ultrasound-guided supraclavicular stellate ganglion block. Considering the existing anatomical structures of the targeted area.

RESULTS AND CONCLUSIONS

We hope that we can provide fewer complications and additional benefits with this new approach.

Exploring the need for reconsideration of trial design in perioperative outcomes research: a narrative review

"Enhanced recovery after surgery" is a multimodal effort to control perioperative pathophysiology and improve outcome. However, despite advances in perioperative care, postoperative complications and the need for hospitalisation and prolonged recovery continue to be challenging. This is further complicated by procedure-specific and patient-associated risk factors, given the increase in the number of elderly and frail patients with multiple comorbidities undergoing surgery. This paper is a critical assessment of current methodology for trials in perioperative medicine. We make a plea to reconsider the design of future interventional trials to improve surgical outcome, based upon studies of potentially effective interventions, but often without improvements in recovery. The complexity of perioperative pathophysiology necessitates a procedure- and patient-specific approach whenever outcome is assessed or interventions are planned. With improved understanding of perioperative pathophysiology, the way to improve outcomes looks promising, provided that knowledge and established enhanced recovery programmes are integrated in trial design.

Funding

None.

Prediction of pain using electrocardiographic-derived autonomic measures: A systematic review

BACKGROUND AND OBJECTIVE

Pain is a major clinical challenge, and understanding the pathophysiology is critical for optimal management. The autonomic nervous system reacts to pain stimuli, and autonomic dysfunction may predict pain sensation. The most used assessment of autonomic function is based on electrocardiographic measures, and the ability of such measures to predict pain was investigated.

DATABASES AND DATA TREATMENT

English articles indexed in PubMed and EMBASE were reviewed for eligibility and included when they reported electrocardiographic-derived measures' ability to predict pain response. The quality in prognostic studies (QUIPS) tool was used to assess the quality of the included articles.

RESULTS

The search revealed 15 publications, five on experimental pain, five on postoperative pain, and five on longitudinal clinical pain changes, investigating a total of 1069 patients. All studies used electrocardiographically derived parameters to predict pain assessed with pain thresholds using quantitative sensory testing or different scales. Across all study modalities, electrocardiographic measures were able to predict pain. Higher parasympathetic activity predicted decreased experimental, postoperative, and long-term pain in most cases while changes in sympathetic activity did not consistently predict pain.

CONCLUSIONS

Most studies demonstrated that parasympathetic activity could predict acute and chronic pain intensity. In the clinic, this may be used to identify which patients need more intensive care to prevent, for example postoperative pain and develop personalized chronic pain management.

SIGNIFICANCE

Pain is a debilitating problem, and the ability to predict occurrence and severity would be a useful clinical tool. Basal autonomic tone has been suggested to influence pain perception. This systematic review investigated electrocardiographic-derived autonomic tone and found that increased parasympathetic tone could predict pain reduction in different types of pain.

Transauricular nerve stimulation in acute ischaemic stroke requiring mechanical thrombectomy: Protocol for a phase 2A, proof-of-concept, sham-controlled randomised trial

BACKGROUND

Labile blood pressure after acute ischaemic stroke requiring mechanical thrombectomy is independently associated with poor patient outcomes.

OBJECTIVES

This study protocol describes is designed to determine whether transauricular nerve stimulation, improves baroreflex sensitivity, reduces blood pressure variability in the first 24 hours after acute ischaemic stroke requiring mechanical thrombectomy.

DESIGN: PHASE 2A, PROOF-OF-CONCEPT, SHAM-CONTROLLED RANDOMISED TRIAL

Methods and Analysis: 36 individuals undergoing mechanical thrombectomy for acute ischaemic stroke with established hypertension aged >18 years will be randomly allocated to receive bilateral active or sham transauricular nerve stimulation for the duration of the mechanical thrombectomy procedure (AffeX-CT/001 investigational device). The intervention will be repeated for 1h the morning following the mechanical thrombectomy. Non-invasive blood pressure will be measured ≥2h for 24h after mechanical thrombectomy. Holter electrocardiographic monitoring will be recorded during transauricular nerve stimulation. Participants, clinicians and investigators will be masked to treatment allocations. The primary outcome will be the coefficient of variation of systolic blood pressure. Secondary outcomes include additional estimates of blood pressure variability and time/frequency-domain measures of autonomic cardiac modulation An adjusted sample size of 36 patients is required to have a 90% chance of detecting, as significant at the 5% level, a difference in the coefficient of variation in systolic blood pressure of 5±4mmHg between sham and active stimulation [assuming 5% non-compliance rate in each group]. Ethics: confirmed on 16 March 2023 by HRA and Health and Care Research Wales ethics committee (reference 23/WA/0013).

DISCUSSION

This study will provide proof-of-concept data that examines whether non-invasive autonomic neuromodulation can be used to favourably modify blood pressure and autonomic control after acute ischaemic stroke requiring mechanical thrombectomy.

TRIAL REGISTRATION

Trial registration number: NCT05417009.

M1-Type Microglia-Derived Extracellular Vesicles Overexpressing IL-1R1 Promote Postoperative Cognitive Dysfunction by Regulating Neuronal Inflammation

Postoperative cognitive dysfunction (POCD) is a common complication after surgical anesthesia, mainly manifested as memory impairment, decreased attention, and cognitive function with mood and personality changes. Activated microglia (M1-type microglia) have been demonstrated to release inflammatory substances (IL-1β, TNF-α, etc.) that cause neuronal degeneration and death by activating the NF-κB signaling pathway and upregulating Caspase-3 and Bax. However, the pathogenesis of POCD is still not fully understood and needs further research. In the present study, we investigated the effect of M1-type microglia-derived extracellular vesicles (EVsM1-Microglia) in the pathological process of POCD. The levels of NF-κB phosphorylation and IL-1β protein expression in hippocampal neurons were significantly increased in the Surgery group, while PSD95 and MAP2 were significantly decreased. Surgery induced microglia activation, synapse-associated protein decrease, and neuronal degeneration in hippocampus. And the amount of spine and mushroom spine significantly decreased in surgical mice, which was reverted in the presence of IL-1R1 siRNA. In addition, EVsM1-Microglia promoted synaptic loss and neuron degeneration independent of surgery and microglia activation. Furthermore, EVsM1-Microglia promoted memory defects in surgical mice. We demonstrated that EVsM1-Microglia with high expression of IL-1R1 promote POCD development by regulating neuronal inflammation.

Effect of transauricular nerve stimulation on perioperative pain: a single-blind, analyser-masked, randomised controlled trial

BACKGROUND

Activation of central autonomic pathways, including those regulating the arterial baroreflex, might reduce acute pain. We tested the hypothesis that transcutaneous auricular nerve stimulation (TAN) reduces pain after orthopaedic trauma surgery through autonomic modulation.

METHODS

A total of 86 participants aged >18 yr were randomly assigned to 50 min of either sham or active bilateral TAN, undertaken before, and again 24 h after, surgery for orthopaedic trauma. The primary outcome was absolute change in pain 24 h postoperatively, comparing the 100 mm visual analogue scale (VAS) before and after TAN. Secondary outcomes included the minimal clinically important difference in pain (>10 mm increase or reduction in VAS) before/after surgery, using intention-to-treat analysis. Holter monitoring, the analysis of which was masked to allocation, quantified autonomic modulation of heart rate.

RESULTS

From June 22, 2021 to July 7, 2022, 79/86 participants (49 yr; 45% female) completed TAN before and after surgery. For the primary outcome, the mean reduction in VAS was 19 mm (95% confidence interval [CI]: 12-26) after active TAN (n=40), vs 10 mm (95% CI: 3-17) after sham TAN (n=39; P=0.023). A minimally clinically important reduction in postoperative pain occurred in 31/40 (78%) participants after active TAN, compared with 15/39 (38%) allocated to sham TAN (odds ratio 5.51 [95% CI: 2.06-14.73]; P=0.001). Only active TAN increased heart rate variability (log low-frequency power increased by 0.19 ms2 [0.01-0.37 ms2]). Prespecified adverse events (auricular skin irritation) occurred in six participants receiving active TAN, compared with two receiving sham TAN.

CONCLUSION

Bilateral TAN reduces perioperative pain through autonomic modulation. These proof-of-concept data support a non-pharmacological, generalisable approach to improve perioperative analgesia.

Trans-auricular vagus nerve stimulation to reduce perioperative pain and morbidity: protocol for a single-blind analyser-masked randomised controlled trial

Background

Established or acquired loss of parasympathetic vagal tone is associated with complications, including pain, after noncardiac surgery. We describe a study protocol designed to test the hypothesis that transcutaneous auricular nerve stimulation may preserve efferent parasympathetic activity to reduce pain and morbidity after noncardiac surgery.

Methods

Participants aged >18 yr scheduled for urgent/elective orthopaedic surgery (n=86) will be randomly allocated to bilateral transcutaneous auricular nerve stimulation or sham protocol for 50 min at the same time of day, before and 24 h after surgery. Holter monitoring, the analysis of which is masked to allocation, will quantify autonomic modulation of HR. The primary outcome will be pain, quantified by absolute changes in VAS 24 h after surgery following sham or stimulation. Secondary outcomes include presence or absence of >10 mm change in the 100 mm VAS (which defines a minimum clinically important change) and postoperative morbidity (Postoperative Morbidity Survey) before and 24 h after surgery. The relationship between the explanatory variable (HR variability), VAS, and morbidity will be examined using a multilevel (mixed-error component) regression model. Safety and complications of the intervention will also be recorded. The study was approved by the NHS Research Ethics Committee (21/LO/0272). As of 25 December 2021, 34/86 participants (mean [standard deviation] age: 48 [19] yr; 14 females [41.2%]) have been recruited, with complete collection of Holter data.

Conclusions

This phase 2b study will explore whether noninvasive autonomic neuromodulation may reduce pain or morbidity using trans-auricular vagus nerve stimulation, providing proof-of-concept data for a non-pharmacological, generalisable approach to improve perioperative outcomes.

Clinical trial registration

Researchregistry7566.