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Surgical correction without complex osteotomy procedures can be utilized in the surgical treatment for adult spinal deformity (ASD). Although it reduces the incidence of postoperative neurological deficits, it remains associated with high-risk and time-consuming procedures^1,2 that can lead to prolonged propofol infusion, massive hemorrhage and even neurological injury^3,4. Therefore, continuous and synchronous assessment of the spinal neurological function is essential to limit or prevent the deficits. Intraoperative neuromonitoring (IONM) technique by combining somatosensory- and motor-evoked potential (SSEP and MEP) can assess real-time spinal neurological function. The technique helps predict postoperative neurological prognosis⁵, and it presents excellent diagnostic⁶ and moderate prognostic⁷ values in spinal surgery. However, a high rate of progressive suppression or even false-positive changes during prolonged exposure to GABAergic agents, extended surgical duration, and massive blood loss are major challenges associated with IONM^{8,9,10,11,12,13,14,15,16,17}. False-positive waveforms could be interpreted erroneously as neurological injury, which can weaken the diagnostic and prognostic value⁵. Consequently, limiting or mitigating the influence of these risk factors by incorporating adjuvant anesthetics and/or alternative techniques that do not adversely affect IONM waveforms can be beneficial in ASD surgery⁹.

Dexmedetomidine could be served as an adjunct to total intravenous anesthesia (TIVA) to reduce the consumption of opioids¹⁸ and propofol¹⁹. Notably, large doses of GABAergic drugs can attenuate IONM signals^8,20,21 during spinal surgeries. Furthermore, pre-emptive regional analgesia via erector spinae plane block (ESPB) with local anesthetic (LA) has been shown to provide excellent intra- and post-operative analgesia, as well as facilitate early mobilization and recovery after posterior cervical²², thoracic²³, and lumbar²⁴ spine surgeries. Recent studies^22,25 demonstrated ESPB can also provide stable hemodynamic profiles, significantly reduce intraoperative blood loss, and shorten surgical duration in spinal surgeries. Furthermore, Diwan et al²⁶ in one case report of ESPB technique in scoliosis patients demonstrated no interference with evoked potentials. In contrast, Furutani et al.²⁷ demonstrated that SSEP/MEP waveforms can be suppressed by high-dose ropivacaine when it was administered regionally.

The effects of ESPB with ropivacaine combined with dexmedetomidine administered systemically on SSEP/MEP during adult spinal deformity (ASD) surgery have not been elucidated. Therefore, we performed a randomized, prospective study to assess the impacts of dexmedetomidine delivered intravenously at a constant rate (0.5 μg kg⁻¹ h⁻¹) as an adjuvant to TIVA, in combination with ultrasound-guided bilateral bi-level single-shot ESPB (with a total of 40 ml 0.2% ropivacaine) on SSEP/MEP during surgical correction for ASD. Our primary endpoint was to investigate the effect of low-dose intravenous dexmedetomidine infusion combined with ropivacaine administered via ESPB on IONM waveforms in patients undergoing ASD surgery. Our secondary endpoint is to compare the incidence of postoperative side effects between patients receiving TIVA alone and those in the DE group.

Ethics

This study was a prospective, randomized, double-blind clinical trial. Ethical approval for this study was provided by the Ethics Committee and Institutional Review Board (IRB, No. 202201007) of Xi’an Honghui Hospital, Xi’an Jiaotong University, Xi’an, China (Chairperson Prof. Xu) on 9th January 2022. Written informed consent was obtained from all subjects participating in the trial. The trial was registered before patient enrollment at ChineseClinicalTrialRegistry.cn (ChiCTR2200057123) on 1st March 2022. This study complied with the Declaration of Helsinki, and the report follows the Consolidated Standard of Reporting Trials (CONSORT) guidelines. 102 patients were enrolled in our hospital from March 2022 and March 2024.

Patients

Inclusion criteria are as follows: (1) age between 18 and 70 years and ASA status between I and III; and (2) computed tomography (CT) studies showed adult scoliosis evidence. Exclusion criteria are as follows: (1) patients with poor quality of IONM baseline waveforms, or IONM signals absent^28,29; (2) patients suffering from epilepsy, or stroke with residual neurological disorder; (3) patients with systemic or local sepsis; (4) Patients with bleeding disorder; (5) to avoid the effect of intraoperative neurological injuries caused by surgical procedures on SSEP/MEP, waveforms changed only in lower extremities.Because when SSEP and/or MEP signals change exclusively in the lower extremities while the upper extremities signals remain unchanged, this pattern specifically suggests intraoperative spinal nerve injury. Therefore, patients who meet the criteria were systematically excluded from the study cohort to ensure the analysis specificity.

Anesthesia protocol

Anesthesia was induced by target-controlled infusion (TCI) with 2.0 to 3.0 μg ml^–1 propofol and sufentanil 0.40 to 0.60 μg kg^–1, midazolam 0.02 mg kg^–1, and rocuronium 0.50 mg kg^–1. Anesthesia was maintained by the Diprifusor propofol infusion system, with a TCI of propofol 2.0 to 4.0 μg ml^-1, remifentanil 0.15 to 0.30 μg kg⁻¹ min⁻¹, and dexmedetomidine infused at a constant infusion rate (0.50 μg kg⁻¹ h⁻¹) ^7,30,31 from skin incision to muscle closure. The depth of anesthesia was adjusted by varying the propofol or remifentanil doses based on bispectral monitor (BIS, Aspect Medical Systems Inc., United States) (40–60), and mean arterial pressure (MAP) was maintained between 70 and 80 mmHg.

Bilateral bi-level single-shot ESPB technique

Pre-emptive regional analgesia with ropivacaine through bilateral bi-level single-shot ESPB was performed by an experienced anesthesiologist. After anesthesia induction, the patients were placed prone. The anesthesiologist placed a high-frequency linear transducer (SonoSite HFL 50x; SonoSite Inc., USA) lateral to spinous process in both longitudinal and transverse planes at T₅ and T₁₀ vertebral levels. After identifying T₅ transverse process tip, the LA solution (0.2% ropivacaine (AstraZeneca AB, Sweden)) was injected by a 22-gauge 50-mm echogenic needle (B. Braun, Hessen, Germany) below the erector spinae muscle (ESM). The anesthesiologist performed a similar procedure on the other side at the same level, and also performed bilaterally at the T₁₀ level³². We administered a total of 20 ml 0.2% ropivacaine bilaterally at each level.

Randomization and blinding

Randomization was completed by SPSS v26.0 software (IBM; Armonk, NY). The randomization results were prepared by an independent bio-statistician and were concealed in sealed envelopes. After anesthesia induction, the eligible patients were randomly allocated to receive continuous dexmedetomidine infusion at a rate of 0.5 μg kg⁻¹ h⁻¹ from skin incision to muscle closure (Group DE), or a volume-matched continuous infusion of 0.9% saline (Group T) in a 1:1 ratio, according to the randomization results.

The testing drugs were prepared by an independent anesthesiologist and allocated to the corresponding anesthesiologists. IONM signals were recorded by an independent team of neurophysiologists. So, the surgeons, patients, anesthesiologists, and neurophysiologists were blinded to the treatment groups.

Acquisition of IONM signals

For MEP monitoring, targeting muscle recording points including the first dorsal interosseous muscles, deltoid, brachioradialis, and abductor pollicis longus for the upper limbs, and the flexor hallucis brevis and abductor hallucis (AH) for the lower limbs^33,34. According to the 10/20 EEG international system, the stimulation electrodes were inserted subcutaneously over motor cortex regions C3–C4. Recording electrodes are placed into the corresponding muscles. MEP was elicited by a constant voltage (220–360 V), with a duration of 300 μs. The signal analysis time was 100 ms. The bandpass filter was between 10 and 1,500 Hz. Before eliciting MEP signals, a real-time train-of-four (TOF) ratio was recorded to rule out undesirable inhibitory effects of muscle relaxants on MEP amplitude^7,30.

For SSEP monitoring, stimulation sites included the median nerve at upper limbs and the posterior tibial nerve at the lower limbs. While we recorded SSEP/MEP signals from both the lower proximal extremities and the lower distal extremities. However, we ultimately adopted the abductor pollicis longus (APL) and abductor hallucis (AH) muscles for signal recording, as these targeting muscles are well-established in the literature could provide the optimal IONM signal during the spinal surgery¹². Median nerve stimulation was performed bilaterally at the wrist, and posterior tibial nerve stimulation was performed bilaterally at the head of the fibula or the medial malleolus of the ankle. The parameters of obtaining SSEP were as follows: the median nerve was stimulated at 15 mA, and the posterior tibial nerves were stimulated at 25 mA. The bandpass filter was between 30 and 300 Hz, and the waveforms were displayed in a 100 ms window. 350 to 450 stimulation repetition is averaged to obtain each SSEP sweep.

To avoid the effects of intraoperative neurological injuries on SSEP/MEP in the lower limbs, MEP waveforms were recorded from APL muscles (control), and SSEP parameters were recorded from the median nerve³⁵ (control). Furthermore, patients whose SSEP and /or MEP waveforms changed only in the lower extremities were excluded. Because when SSEP and/or MEP change exclusively in the lower extremities while the upper extremities signals remain unchanged, this pattern specifically suggests intraoperative spinal nerve injury. Therefore, patients who meet the criteria were systematically excluded from the study cohort to ensure the analysis specificity.

A change in SSEP was defined as an increase of more than 10% in latency, and/or a decrease of greater than 50% in amplitude of the baseline waveforms. A change in MEP was defined as a decrease of more than 70% in amplitude of the baseline value. SSEP and MEP change- was defined as a simultaneous change in both SSEP and MEP, and SSEP or MEP change was defined as a change in either or both modalities³⁶.

Time points set for obtaining IONM signals

We aim to explore the effects of ESPB technique combined with dexmedetomidine delivered systemically on the time course of the relative IONM waveforms during ASD surgery. IONM parameters were collected before and after important...(More)

For more info please read, Effects of dexmedetomidine combined with erector spinae plane block on intraoperative neuromonitoring, by Scientific Reports