Changes in transcranial motor evoked potentials during hemorrhage are associated with increased serum propofol concentrations

Utility of somatosensory- and motor-evoked potential change thresholds in surgical treatment for thoracic spinal stenosis based on different pathologies

BACKGROUND CONTEXT

Thoracic spinal stenosis (TSS) is secondary to different pathologies that differ in clinical characteristics and surgical outcomes.

PURPOSE

This study aimed to determine the optimal warning thresholds for combined somatosensory-evoked potentials (SSEP) and motor-evoked potentials (MEP) for predicting postoperative neurological deterioration in surgical treatment for TSS based on different pathologies. Additionally, we explored the correlation between SSEP/MEP monitoring and postoperative spinal neurological function.

STUDY SETTING

Retrospective study.

PATIENT SAMPLE

Two hundred and five patients.

OUTCOME MEASURES

We obtained perioperative modified Japanese Orthopedic Association (mJOA) scores to assess spinal neurological function.

METHODS

The data collected in this study included demographic data, intraoperative neurophysiological monitoring (IONM) signals, and perioperative neurological function assessments. To determine the optimal IONM warning threshold, a receiver operating characteristic (ROC) curve was used. Additionally, Pearson correlation analysis was conducted to determine the correlation between IONM signals and clinical neurological conditions.

RESULTS

A total of 205 consecutive patients were eligible. Forty-one patients had thoracic disc herniation (TDH), 14 had ossification of the posterior longitudinal ligament (OPLL), 124 had ossification of the ligamentum flavum (OLF), and 26 had OPLL+OLF. The mean mJOA scores before surgery and 3 months after surgery were 7.0 and 7.9, respectively, resulting in a mean mJOA recovery rate (RR) of 23.1%. The average postoperative mJOA RRs for patients with TDH, OPLL, OLF, and OPLL+OLF were 24.8%, 10.4%, 26.8%, and 11.2%, respectively. Patients with OPLL+OLF exhibited a more stringent threshold for IONM changes. This included a lower amplitude cutoff value (a decrease of 49.0% in the SSEP amplitude and 57.5% in the MEP amplitude for short-term prediction) and a shorter duration of waveform change (19.5 minutes for SSEP and 22.5 minutes for MEP for short-term prediction). On the other hand, patients with TDH had more lenient IONM warning criteria (a decrease of 49.0% in SSEP amplitude and 77.5% in MEP amplitude for short-term prediction; durations of change of 25.5 minutes for SSEP and 32.5 minutes for MEP). However, OPLL patients or OLF patients had moderate and similar IONM warning thresholds. Additionally, there was a stronger correlation between the SSEP amplitude variability ratio and the JOA RR in OPLL+OLF patients, while the correlation was stronger between the MEP amplitude variability ratio and the JOA RR for the other three TSS pathologies.

CONCLUSIONS

Optimal IONM change criteria for prediction vary depending on different TSS pathologies. The optimal monitoring strategy for prediction varies depending on TSS pathologies.

How is depth of anaesthesia assessed in experimental pigs? A scoping review

BACKGROUND

Despite the large number of pigs involved in translational studies, no gold standard depth of anaesthesia indicators are available. We undertook a scoping review to investigate and summarize the evidence that sustains or contradicts the use of depth of anaesthesia indicators in this species.

METHODS

Medline, Embase and CAB abstract were searched up to September 22nd 2022. No limits were set for time, language and study type. Only original articles of in vivo studies using pigs or minipigs undergoing general anaesthesia were included. The depth of anaesthesia indicators reported in the selected papers were divided in two categories: A, indicators purposely investigated as method to assess depth of anaesthesia; B, indicators reported but not investigated as method to assess depth of anaesthesia.

RESULTS

Out of 13792 papers found, 105 were included after the screening process. Category A: 17 depth of anaesthesia indicators were found in 19 papers. Studies were conducted using inhalant anaesthetics as the main anaesthetic agent in the majority of the cases (13/19 = 68.4%), while 3/19 (15.8%) used propofol. The most investigated depth of anaesthesia indicators were bispectral index (8/19 = 42.1%) and spectral edge frequency 95% (5/19 = 26.3%). Contrasting results about the specific usefulness of each depth of anaesthesia indicators were reported. Category B: 23 depth of anaesthesia indicators were found in 92 papers. The most reported depth of anaesthesia indicators were: motor response following a stimulus (37/92 = 40.2%), depth of anaesthesia scores (21/92 = 23.3%), bispectral index (16/92 = 17.8%) and spectral edge frequency 95% (9/92 = 9.8%).

CONCLUSION

Results highlight the lack of scientifically valid and reliable indicators to ensure adequate depth of anaesthesia in pigs.

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.

Intraoperative Neuromonitoring Auxiliary Significance of DNEP for MEP-positive Event During Severe Spinal Deformity Surgery

STUDY DESIGN

This was a retrospective analysis.

OBJECTIVE

The objective of this study was to assess the intraoperative neuromonitoring auxiliary significance of descending neurogenic-evoked potential (DNEP) for motor-evoked potential (MEP) during severe spinal deformity surgery when MEP-positive event occurs.

SUMMARY OF BACKGROUND DATA

MEP detection is the most widely applied neurological monitoring technique in spinal deformity surgery. MEP is quite vulnerable to anesthesia, blood pressure, and other intraoperative factors, leading to a high false-positive rate of MEP (3.2%-45.0%), which has greatly interfered with the surgical process. At present, the widely used "presence-or-absence" alarm criteria of MEP is not enough to solve the problem of false positive of MEP.

METHODS

A total of 205 cases undergoing severe spinal deformity correction were retrospectively studied. Overall, 74 MEP-positive cases were classified as 2 subgroups: DNEP (+) and DNEP (-) groups. The MEP recovery, wake-up test, and Frankle grade were used to assess the neurological functions. The perioperative and long-term neurological outcomes were assessed.

RESULTS

There were significant differences in preoperative scoliosis angle and kyphosis angle between DNEP (-) and DNEP (+) groups. Patients in DNEP (-) group showed more MEP improvement (81.5%), compared with the DNEP (+) group (53.2%). The Wake-up test showed 59.3% motor function deficit cases in DNEP (-) group, which was lower than the 87.2% in DNEP (+) group. More patients in DNEP (-) group had normal nerve function (Frankel level E) than those in DNEP (+) group immediately after surgery, as well as at follow-up.

CONCLUSIONS

MEP-positive cases with intraoperative DNEP (-) showed superior prognosis after severe spinal deformity surgery. Intraoperative DNEP could be regarded as an important quantitative tool to assist MEP to monitor neurological injury and can serve as a temporary substitution monitoring technique after MEP is lost.

Influence of hemorrhage and subsequent fluid resuscitation on transcranial motor-evoked potentials under desflurane anesthesia in a swine model

PURPOSE

Hemorrhage increases the effect of propofol and could contribute to false-positive transcranial motor-evoked potential (TcMEP) responses under total intravenous anesthesia (TIVA). We investigated the influence of hemorrhage and subsequent fluid resuscitation on TcMEPs under desflurane anesthesia.

METHODS

Sixteen swine (25.4 ± 0.4 kg) were anesthetized with a 4% end-tidal desflurane concentration (EtDes), which was incrementally increased to 6%, 8%, and 10% and then returned to 4% every 15 min. This procedure was repeated twice (baseline). After baseline measurements, animals were allocated to either the hemorrhage (n = 12) or control (n = 4) group. In the hemorrhage group, 600 ml of blood was removed and the EtDes protocol described above was applied. Hypovolemia was resuscitated using 600 ml of hydroxyethyl starch and the EtDes protocol was applied again. TcMEPs were measured at each EtDes. In the control group, measurements were performed without hemorrhage or fluid infusion.

RESULTS

TcMEP responses were observed in all conditions in all limbs with 4% EtDes (0.4 MAC). TcMEP amplitudes decreased according to the EtDes to a greater degree in the lower limbs compared with the upper limbs. Hemorrhage enhanced the effect of desflurane on TcMEP amplitudes, and decreased TcMEP by 41 ± 12% in upper limbs and 63 ± 17% in lower limbs compared with baseline. Subsequent fluid resuscitation did not reverse TcMEP amplitudes.

CONCLUSIONS

TcMEP amplitudes decrease during hemorrhage under desflurane anesthesia. This phenomenon might result from an enhanced effect of desflurane on the spinal motor pathway without increasing the desflurane concentration.

Characteristics of false-positive alerts on transcranial motor evoked potential monitoring during pediatric scoliosis and adult spinal deformity surgery: an "anesthetic fade" phenomenon

OBJECTIVE

Transcranial motor evoked potential (TcMEP) monitoring may be valuable for predicting postoperative neurological complications with a high sensitivity and specificity, but one of the most frequent problems is the high false-positive rate. The purpose of this study was to clarify the differences in the risk factors for false-positive TcMEP alerts seen when performing surgery in patients with pediatric scoliosis and adult spinal deformity and to identify a method to reduce the false-positive rate.

METHODS

The authors retrospectively analyzed 393 patients (282 adult and 111 pediatric patients) who underwent TcMEP monitoring while under total intravenous anesthesia during spinal deformity surgery. They defined their cutoff (alert) point as a final TcMEP amplitude of ≤ 30% of the baseline amplitude. Patients with false-positive alerts were classified into one of two groups: a group with pediatric scoliosis and a group with adult spinal deformity.

RESULTS

There were 14 cases of false-positive alerts (13%) during pediatric scoliosis surgery and 62 cases of false-positive alerts (22%) during adult spinal deformity surgery. Compared to the true-negative cases during adult spinal deformity surgery, the false-positive cases had a significantly longer duration of surgery and greater estimated blood loss (both p < 0.001). Compared to the true-negative cases during pediatric scoliosis surgery, the false-positive cases had received a significantly higher total fentanyl dose and a higher mean propofol dose (0.75 ± 0.32 mg vs 0.51 ± 0.18 mg [p = 0.014] and 5.6 ± 0.8 mg/kg/hr vs 5.0 ± 0.7 mg/kg/hr [p = 0.009], respectively). A multivariate logistic regression analysis revealed that the duration of surgery (1-hour difference: OR 1.701; 95% CI 1.364-2.120; p < 0.001) was independently associated with false-positive alerts during adult spinal deformity surgery. A multivariate logistic regression analysis revealed that the mean propofol dose (1-mg/kg/hr difference: OR 3.117; 95% CI 1.196-8.123; p = 0.020), the total fentanyl dose (0.05-mg difference; OR 1.270; 95% CI 1.078-1.497; p = 0.004), and the duration of surgery (1-hour difference: OR 2.685; 95% CI 1.131-6.377; p = 0.025) were independently associated with false-positive alerts during pediatric scoliosis surgery.

CONCLUSIONS

Longer duration of surgery and greater blood loss are more likely to result in false-positive alerts during adult spinal deformity surgery. In particular, anesthetic doses were associated with false-positive TcMEP alerts during pediatric scoliosis surgery. The authors believe that false-positive alerts during pediatric scoliosis surgery, in particular, are caused by "anesthetic fade."

Predictors for blood loss in pediatric patients younger than 10 years old undergoing primary posterior hemivertebra resection: a retrospective study

Background

Blood loss during hemivertebra resection may be substantial. Few studies have examined the risk factors of blood loss undergoing hemivertebra resection, especially those in patients under 10 years old.

Methods

Patients under 10 years old diagnosed with congenital scoliosis and hemivertebra were retrospectively included from January 2014 to October 2017. They all had primary posterior hemivertebra resection at Peking Union Medical College Hospital. Perioperative information was collected and multivariable linear logistic regression was performed to determine the independent risk factors of blood loss.

Results

One hundred three patients were included. The mean total blood loss was 346 + 178 ml. The percentage of total blood loss to the EBV was 27.0 + 13.3%. Multivariable linear logistic regression indicated that preoperative total Cobb angle (P = 0.046) and the number of fused levels (P < 0.001) were independent risk factors of total blood loss. Preoperative platelet count and preoperative coagulation function were not associated with blood loss in patients undergoing hemivertebra resection.

Conclusions

Preoperative total Cobb angle and the number of fused levels determined the blood loss for patients undergoing hemivertebra resection.

EOY summary 2018

Clinical monitoring and technology are at the heart of anesthesiology, and new technological developments will help to define how anesthesiology will evolve as a profession. Anesthesia related research published in the JCMC in 2018 mainly pertained to ICU sedation with inhaled agents, anesthesia workstation technology, and monitoring of different aspects of depth of anesthesia.

A motor evoked potential trending system may discriminate outcome: retrospective application with three cases

This report presents a method for tracking Motor Evoked Potential (MEP) amplitudes over the course of a case using a moving least squares linear regression (LSMAs). During a case, newly obtained MEP amplitudes are compared to those predicted by a just previous linear regression (least squares moving average or LSMA). When detected by this comparison, a set criterion amplitude loss will then trigger linear regression of ensuing MEP amplitudes on an expanding step function which tracks the persistence of the amplitude loss for the remainder of the case. Three cases are presented. One in which the patient woke up with a newly acquired weakness in the left tibialis anterior and another in which MEP amplitudes were suddenly lost from the right foot, but after intervention, they were restored again. In a third case the patient again woke up with a new post-operative deficit, but MEP trial sampling had been more limited and variable than in the first two cases. When the linear trending method was applied to the affected myotome in the first case, the expanding step function regression was triggered after the moment of MEP loss and remained at a high level until the end of case. In the second case, the expanding step function regression was also triggered in the relevant myotome at the time of the reported MEP change, but diminished by end of case. In the third case the tracking method again successfully triggered a predictive R-Square despite the limited number of pre-event trials. The R-Square value of the expanding step function regression appears to have discriminative capability with regard to new post-op deficit. Given the importance of the intra-operative MEP for monitoring motor functioning and the high degree of variability that can affect it, the development of new quantitative, statistical methods to detect real from apparent MEP change will be necessary.