Cortical somatosensory-evoked potentials during spine surgery in patients with neuromuscular and idiopathic scoliosis under propofol–remifentanil anaesthesia

A Loading Dose of Dexmedetomidine With Constant Infusion Inhibits Intraoperative Neuromonitoring During Thoracic Spinal Decompression Surgery: A Randomized Prospective Study

Background: The effect of a bolus dose of dexmedetomidine on intraoperative neuromonitoring (IONM) parameters during spinal surgeries has been variably reported and remains a debated topic.

Methods: A randomized, double-blinded, placebo-controlled study was performed to assess the effect of dexmedetomidine (1 μg/kg in 10 min) followed by a constant infusion rate on IONM during thoracic spinal decompression surgery (TSDS). A total of 165 patients were enrolled and randomized into three groups. One group received propofol- and remifentanil-based total intravenous anesthesia (TIVA) (T group), one group received TIVA combined with dexmedetomidine at a constant infusion rate (0.5 μg kg⁻¹ h⁻¹) (D₁ group), and one group received TIVA combined with dexmedetomidine delivered in a loading dose (1 μg kg⁻¹ in 10 min) followed by a constant infusion rate (0.5 μg kg⁻¹ h⁻¹) (D₂ group). The IONM data recorded before test drug administration was defined as the baseline value. We aimed at comparing the parameters of IONM.

Results: In the D₂ group, within-group analysis showed suppressive effects on IONM parameters compared with baseline value after a bolus dose of dexmedetomidine. Furthermore, the D₂ group also showed inhibitory effects on IONM recordings compared with both the D₁ group and the T group, including a statistically significant decrease in SSEP amplitude and MEP amplitude, and an increase in SSEP latency. No significance was found in IONM parameters between the T group and the D₁ group.

Conclusion: Dexmedetomidine delivered in a loading dose can significantly inhibit IONM parameters in TSDS. Special attention should be paid to the timing of a bolus dose of dexmedetomidine under IONM. However, dexmedetomidine delivered at a constant speed does not exert inhibitory effects on IONM data.

The Prognostic Value of Intraoperative Neuromonitoring by Combining Somatosensory- and Motor-Evoked Potentials for Thoracic Spinal Decompression Surgery in Patients with Neurological Deficit

STUDY DESIGN

Retrospective study.

OBJECTIVE

To explore a relation between somatosensory- and motor-evoked potential (SEPs, MEPs) and corresponding thoracic cord function for thoracic spinal decompression surgery (TSDS) in patients with neurological deficit.

SUMMARY OF BACKGROUND DATA

Although SEPs and MEPs monitoring has been developed as an essential technique in spinal surgery. There are limited data on the reliability of using SEPs and MEPs for TSDS and its prognosis.

METHODS

One hundred twenty patients underwent TSDS in our hospital, 91 patients completed the trial. All the patients were divided into three subgroups according to the changes of MEPs and SEPs: neither SEPs nor MEP deteriorated -. Simply MEP deteriorated and both SEPs and MEP deteriorated -. Bispectral (BIS) was used to monitor the depth of sedation, which ranged from 40 to 60 by varying the infusion speed of anesthetics. The pre- and postoperative spinal function was assessed by muscle strength and Japanese Orthopaedic Association (JOA) score at three time points:1) before surgery; 2) immediately after general anesthesia recovery; 3) after 3-month follow-up.

RESULTS

Sixty-nine cases showed neither SEPs nor MEP deteriorated -, 10 cases showed only MEP deteriorated, and 12 cases showed both SEPs and MEP deteriorated -. The patients in the group where neither SEPs nor MEP deteriorated had the best recovery of the extremity muscle strength, the shortest recovery time (8.10 ± 1.60, P < 0.05), and toe movement time (8.50 ± 1.60, P < 0.05). There is a strong correlation between SEPs variability ratio at T4 time point and JOA recovery ratio (JOA RR) in the 3-month follow-up.

CONCLUSION

Combined SEPs and MEPs monitoring are important for TSDS in patients with neurological deficit and it is helpful for evaluating postoperative prognosis. It is more accurate to record SEPs at T4 time point to predict the patients' prognosis.Level of Evidence: 3.

Intraoperative neurophysiologic monitoring in idiopathic scoliosis surgery: a retrospective observational study of new neurologic deficits

PURPOSE

Patients with adolescent idiopathic scoliosis undergoing corrective surgery are at risk for iatrogenic spinal cord injury and subsequent new neurologic deficits (NNDs). Intraoperative neurophysiologic monitoring (IONM) has been used to identify spinal cord injury; however, available data showing that IONM leads to improved clinical outcomes are inconclusive. This exploratory study aimed to examine the incidence of NNDs after idiopathic scoliosis surgery in two pediatric institutions in Canada with a focus on IONM use.

METHODS

Charts of pediatric patients (10-18 yr) with adolescent idiopathic scoliosis who underwent scoliosis correction surgery were retrospectively identified from the operating room database. Data regarding incidence and severity (mild [isolated sensory deficit] vs severe [any motor deficit]) of NNDs as well as demographic and clinical characteristics were extracted.

RESULTS

Of 547 patients reviewed, 359 (66%) underwent IONM and 186 (34%) underwent wake-up test. Neuromonitoring data were missing in two patients. Total incidence of NNDs was 4.9% (95% confidence interval [CI], 3.1 to 6.8). Compared with the wake-up test, patients undergoing IONM were less likely to develop NNDs (unadjusted odds ratio, 0.39; 95% CI, 0.18 to 0.86; P = 0.02). Nevertheless, subgroup analysis did not reveal a statistical difference in severity of those deficits (mild vs severe) with IONM vs wake-up test. Combined anterior and posterior approach was also significantly associated with increased risk of such deficits.

CONCLUSION

This exploratory study revealed that IONM was associated with a reduced overall incidence of NNDs in idiopathic scoliosis correction; however, its impact on the severity of those deficits is questionable. As we were unable to adjust for confounding variables, further research is needed to determine the impact of IONM on NNDs.

Comparison between effect of desflurane/remifentanil and propofol/remifentanil anesthesia on somatosensory evoked potential monitoring during scoliosis surgery-A randomized controlled trial

BACKGROUND

Drugs used in anesthesia can affect somatosensory evoked potential (SSEP) monitoring, which is used routinely for intraoperative monitoring of spinal cord integrity during spinal surgery.

OBJECTIVE

The objective of this study was to determine whether combined total intravenous anesthesia (TIVA) technique with propofol/remifentanil is associated with less SSEP suppression when compared to combined volatile agent desflurane/remifentanil anesthesia during corrective scoliosis surgery at a comparable depth of anesthesia.

DESIGN

It is a randomized controlled trial.

SETTING

The study was conducted at the Single tertiary University Hospital during October 2014 to June 2015.

PATIENTS

Patients who required SSEP and had no neurological deficits, and were of American Society of Anesthesiologist I and II physical status, were included. Patients who had sensory or motor deficits preoperatively and significant cardiovascular and respiratory disease were excluded. A total of 72 patients were screened, and 67 patients were randomized and allocated to two groups: 34 in desflurane/remifentanil group and 33 in TIVA group. Four patients from desflurane/remifentanil group and three from TIVA group were withdrawn due to decrease in SSEP amplitude to <0.3 µV after induction of anesthesia. Thirty patients from each group were analyzed.

INTERVENTIONS

Sixty-seven patients were randomized to receive TIVA or desflurane/remifentanil anesthesia.

MAIN OUTCOME MEASURES

The measurements taken were the amplitude and latency of SSEP monitoring at five different time points during surgery: before and after the induction of anesthesia, at skin incision, at pedicle screw insertion, and at rod insertion.

RESULTS

Both anesthesia techniques, TIVA and desflurane/remifentanil, resulted in decreased amplitude and increased latencies of both cervical and cortical peaks. The desflurane/remifentanil group had a significantly greater reduction in the amplitude ( p = 0.004) and an increase in latency ( p = 0.002) of P40 compared with the TIVA group. However, there were no differences in both amplitude ( p = 0.214) and latency ( p = 0.16) in cervical SSEP between the two groups.

CONCLUSIONS

Compared with TIVA technique, desflurane/remifentanil anesthesia caused more suppression in cortical SSEP, but not in cervical SSEP, at a comparable depth of anesthesia.

Transcranial Motor-Evoked Potentials Are More Readily Acquired Than Somatosensory-Evoked Potentials in Children Younger Than 6 Years

BACKGROUND

There is a general belief that somatosensory-evoked potentials (SSEPs) are more easily obtained than transcranial motor-evoked potentials (TcMEPs) in children younger than 6 years. We tested this assumption and the assumption that motor-evoked potentials are rarely obtained in children younger than 2 years.

METHODS

The records of all patients who were monitored during surgical procedures between April 1, 2010, and June 30, 2013, were reviewed and those who were younger than 72 months at the time of surgery were identified and analyzed for the rate of obtaining clinically useful SSEPs and motor-evoked potentials. Subgroup analysis was performed by age.

RESULTS

A total of 146 patients were identified, 9 had SSEPs without TcMEPs monitored, 117 had both TcMEPs and SSEPs monitored, and the remainder had only electromyographic monitoring. All patients who were to have TcMEPs recorded received a total IV anesthetic. Among the 117 patients who had both SSEPs and TcMEPs monitored, clinically relevant TcMEPs were obtained more frequently than SSEPs (110/117 vs 89/117; χ = 14.82; P = 0.00012). There were significant differences between the rates of obtaining SSEPs and TcMEPs in the 0- to 23-month (P = 0.0038) and 24- to 47-month (P = 0.0056) age groups. Utilization of a double-train stimulation technique facilitated obtaining TcMEPs in the youngest patients.

CONCLUSIONS

TcMEPs can be obtained more easily than SSEPs in patients younger than 72 months if a permissive anesthetic technique is used. The success rate for obtaining TcMEPs can be further enhanced by the use of a temporal facilitation (double-train) stimulation technique.

Influence of vertebral column distraction on spinal cord volume: an experimental study in a goat model

INTRODUCTION

Spinal cord injury may be related to excessive distraction of the spinal cord during surgical correction of spinal deformities by vertebral column resection. This study aimed to investigate how vertebral column distraction influences spinal cord volume to establish the safe range in a goat model.

MATERIALS AND METHODS

A vertebral column resection was performed on the tenth thoracic vertebra of 11 goats. The spinal cord was distracted until the somatosensory evoked potential signals were decreased to 50 % from baseline amplitude or were delayed by 10 % of the baseline peak latency. The osteotomy segment was stabilized with a PEEK mesh cage filled with bone graft, and the pedicle screws on the rods were then tightened in this position. Spinal cord volume was calculated using Mimics software, and T10 height, disk height, osteotomy segment height, and spinal segment height were measured using the MRI image workstation.

RESULTS

Three goats were excluded, and data obtained from the eight remaining goats were analyzed. The safe limit of distraction distance was 11.8 ± 3.65 mm, and the distraction distance was strongly correlated with the difference between the pre- and postoperative measurements (d value) of spinal cord volume per 1 mm of osteotomy segment height (r = -0.952, p < 0.001), but was not correlated with T10 body height (r = 0.16, p = 0.71), spinal segment height (r = 0.29, p = 0.49), disk height (r = -0.12, p = 0.98), or the d value (pre-post) of spinal cord volume per 1 mm of spinal segment height (r = 0.45, p = 0.26). The mean d value (pre-post) of spinal cord volume per 1 mm of osteotomy segment height was 10.05 ± 0.02 mm(3) (range 10.02-10.08 mm(3)).

CONCLUSION

The maximum change in spinal cord volume per 1-mm change in height was in the osteotomy segment, and its safe limit was 10.05 ± 0.02 mm(3). The safe limit of spinal cord distraction can be calculated using the spinal cord volume per unit 1-mm change in height.

Relationship between Spinal Cord Volume and Spinal Cord Injury due to Spinal Shortening

Vertebral column resection is associated with a risk of spinal cord injury. In the present study, using a goat model, we aimed to investigate the relationship between changes in spinal cord volume and spinal cord injury due to spinal shortening, and to quantify the spinal cord volume per 1-mm height in order to clarify a safe limit for shortening. Vertebral column resection was performed at T10 in 10 goats. The spinal cord was shortened until the somatosensory-evoked potential was decreased by 50% from the baseline amplitude or delayed by 10% relative to the baseline peak latency. A wake-up test was performed, and the goats were observed for two days postoperatively. Magnetic resonance imaging was used to measure the spinal cord volume, T10 height, disc height, osteotomy segment height, and spinal segment height pre- and postoperatively. Two of the 10 goats were excluded, and hence, only data from eight goats were analyzed. The somatosensory-evoked potential of these eight goats demonstrated meaningful changes. With regard to neurologic function, five and three goats were classified as Tarlov grades 5 and 4 at two days postoperatively. The mean shortening distance was 23.6 ± 1.51 mm, which correlated with the d-value (post-pre) of the spinal cord volume per 1-mm height of the osteotomy segment (r = 0.95, p < 0.001) and with the height of the T10 body (r = 0.79, p = 0.02). The mean d-value (post-pre) of the spinal cord volume per 1-mm height of the osteotomy segment was 142.87 ± 0.59 mm³ (range, 142.19–143.67 mm³). The limit for shortening was approximately 106% of the vertebral height. The mean volumes of the osteotomy and spinal segments did not significantly change after surgery (t = 0.310, p = 0.765 and t = 1.241, p = 0.255, respectively). Thus, our results indicate that the safe limit for shortening can be calculated using the change in spinal cord volume per 1-mm height.

Pediatric scoliosis surgery--is postoperative intensive care unit admission really necessary?

BACKGROUND

It is common practice for patients to be admitted to the intensive care unit following scoliosis surgery, because of the prolonged anesthesia, the need for efficient pain control and the known immediate postoperative complications. However, this may be unnecessary in many patients.

PURPOSE

We aimed to establish possible associations between pre- and perioperative parameters and early postoperative complication rates, in particular the need for prolonged mechanical ventilation (>1 day), and the presence of major complications in children undergoing primary spinal fusion by thoracolumbar spine instrumentation.

METHODS

We conducted a retrospective review of children undergoing primary scoliosis surgery at a university-affiliated general hospital from 1998 to 2008.

RESULTS

Surgical approaches were as follows: anterior spinal fusion, posterior spinal fusion, and combined anterior and posterior fusion. Prior to mid-2005, anesthesia included morphine; thereafter, remifentanil was used. Major complications correlated significantly with neuromuscular scoliosis (NMS) (OR, 4.94; 95% CI, 1.02-24.05), comorbidity conditions (OR, 3.47; 95% CI, 1.16-10.42), and anterior or combined fusion (OR, 7.81; 95% CI, 2.12-28.57). Late extubation correlated significantly with NMS (OR, 31.25; 95% CI, 1.06-100.00) and morphine use during anesthesia (OR, 17.91; 95% CI, 1.44-222.9).

CONCLUSIONS

Relatively young, healthy idiopathic scoliosis children receiving intraoperative remifentanil sedation and undergoing posterior fusion can be successfully managed in regular wards in the immediate postoperative period. However, intensive care unit admission should be considered in NMS patients, patients with comorbidity conditions, those undergoing anterior or combined spinal fusion, and patients whose anesthesia involves long-acting opioids.

Neuromuscular scoliosis

Scoliosis is a common deformity in many types of neuromuscular disease. Severe spinal curvature can cause difficulty in sitting. Conservative and surgical treatment of neuromuscular scoliosis differs from idiopathic scoliosis, being more complex and with a higher complications rate. Non-surgical measures rarely fully control progressive scoliosis, but aim to prevent spinal deformities secondary to muscular hypotonia or contracture. Twenty-four hour bracing should be adjusted throughout growth, and may induce functional impairment and loss of independence. Corrective surgery requires multidisciplinary management and perioperative screening. Pelvic obliquity is commonly associated with neuromuscular scoliosis, making sitting difficult: correction needs to be considered during surgical planning. The goal of surgical correction is to obtain and maintain a well-balanced spine above a well-positioned pelvis. Preoperative multidisciplinary assessment enables potential problems of terrain to be anticipated. Respiratory function investigation will guide possible non-invasive perioperative ventilation. Nutritional and psychosocial assessment should also be incorporated in this preparation, as should overall postoperative care. Implementing this overall strategic planning can achieve a good surgical and functional result in the vast majority of cases.

Remifentanil use in pediatric scoliosis surgery-an effective alternative to morphine (a retrospective study)

PURPOSE

The unique properties of remifentanil make it ideal for pediatric use despite a lack of wide randomized clinical trials and fear of adverse events due to its high potency. We aimed to consolidate preliminary conclusions regarding the efficacy of remifentanil use in pediatric scoliosis surgery.

MATERIALS AND METHODS

The medical charts of children with idiopathic scoliosis who underwent primary spinal fusion between 1998 and 2007 at a large tertiary university-affiliated hospital were retrospectively reviewed and divided into two groups according to anesthetic regime (remifentanil vs. morphine). Demographic, surgery-related details and immediate postoperative course were recorded and compared.

RESULTS

All 36 remifentanil children were extubated shortly after termination of surgery, compared to 2 of the 84 patients in the morphine group. The remaining patients in the morphine group were extubated hours after surgery [5.4 hours; standard deviation (SD) 1.7 hours]. Six remifentanil children were spared routine intensive care hospitalization (vs. 2 morphine children-significant difference). Shorter surgeries [5.6 hours (SD 1.82 hours) vs. 7.14 hours (SD 2.15 hours); p=0.0004] were logged for the remifentanil group. To achieve controlled hypotension during surgery, vasodilator agents were used in the morphine group only. A comparison of early postoperative major or minor complication rates (including neurological and pulmonary complications) between the two groups yielded no significant differences.

CONCLUSION

Remifentanil use can shorten operating time and facilitate earlier spontaneous ventilation and extubation, with less of a need for intensive care hospitalization and no increase in significant complications.

Comparison between Sevoflurane/Remifentanil and Propofol/Remifentanil Anaesthesia in Providing Conditions for Somatosensory Evoked Potential Monitoring during Scoliosis Corrective Surgery

Somatosensory evoked potential (SSEP) monitoring is an important tool in spinal corrective surgery. Anaesthesia has a significant influence on SSEP monitoring and a technique which has the least and shortest suppressant effect on SSEP while facilitating a fast recovery from anaesthesia is ideal. We compared the effect of sevoflurane/remifentanil and propofol/remifentanil anaesthesia on SSEPs during scoliosis corrective surgery and assessed patients’ clinical recovery profiles.

Twenty patients with idiopathic scoliosis receiving surgical correction with intraoperative SSEP monitoring were prospectively randomised to receive sevoflurane/remifentanil anaesthesia or propofol/remifentanil anaesthesia. During surgery, changes in anaesthesia dose and physiological variables were recorded, while SSEP was continuously monitored. A simulated ‘wake-up’ test was performed postoperatively to assess speed and quality of recovery from anaesthesia.

The effects of propofol and sevoflurane resulted in SSEP amplitude variability between 18.0% ± 3.5% to 28.7% ± 5.9% and SSEP latency variability within 1.3% ± 0.4% to 2.6% ± 1.2%. Patients receiving sevoflurane had faster suppression and faster recovery of SSEP amplitude compared to propofol (P <0.05), although propofol anaesthesia showed less within-patient variability in Cz amplitude and latency (P <0.05). On cessation of anaesthesia, time to eye-opening (5.2 vs. 16.5 minutes) and toe movement (5.4 vs. 17.4 minutes) was shorter following sevoflurane (all P <0.05).

These findings indicate that propofol produces a better SSEP signal than sevoflurane. However, adjustments in sevoflurane concentration result in faster changes in the SSEP signal than propofol. Assessment of neurological function was facilitated more rapidly after sevoflurane anaesthesia.