Anesthetic Management Using Multiple Closed-loop Systems and Delayed Neurocognitive Recovery: A Randomized Controlled Trial

BACKGROUND

Cognitive changes after anesthesia and surgery represent a significant public health concern. We tested the hypothesis that, in patients 60 yr or older scheduled for noncardiac surgery, automated management of anesthetic depth, cardiac blood flow, and protective lung ventilation using three independent controllers would outperform manual control of these variables. Additionally, as a result of the improved management, patients in the automated group would experience less postoperative neurocognitive impairment compared to patients having standard, manually adjusted anesthesia.

METHODS

In this single-center, patient-and-evaluator-blinded, two-arm, parallel, randomized controlled, superiority study, 90 patients having noncardiac surgery under general anesthesia were randomly assigned to one of two groups. In the control group, anesthesia management was performed manually while in the closed-loop group, the titration of anesthesia, analgesia, fluids, and ventilation was performed by three independent controllers. The primary outcome was a change in a cognition score (the 30-item Montreal Cognitive Assessment) from preoperative values to those measures 1 week postsurgery. Secondary outcomes included a battery of neurocognitive tests completed at both 1 week and 3 months postsurgery as well as 30-day postsurgical outcomes.

RESULTS

Forty-three controls and 44 closed-loop patients were assessed for the primary outcome. There was a difference in the cognition score compared to baseline in the control group versus the closed-loop group 1 week postsurgery (-1 [-2 to 0] vs. 0 [-1 to 1]; difference 1 [95% CI, 0 to 3], P = 0.033). Patients in the closed-loop group spent less time during surgery with a Bispectral Index less than 40, had less end-tidal hypocapnia, and had a lower fluid balance compared to the control group.

CONCLUSIONS

Automated anesthetic management using the combination of three controllers outperforms manual control and may have an impact on delayed neurocognitive recovery. However, given the study design, it is not possible to determine the relative contribution of each controller on the cognition score.

End of year summary 2019: anaesthesia and airway management

This end of the year summary reviews anesthesia related manuscripts that have been published in the Journal of Clinical Monitoring and Computing in 2019. Anesthesia is currently defined as being composed of unconsciousness, immobility, and autonomic nervous system (ANS) control (Br J Anaesth;122:e127-e135135, Egan 2019). Pain is a postoperative issue, because by definition unconsciousness implies pain cannot be experienced. We first review work related to these aspect of the profession: unconsciousness (EEG, target control), immobility (muscle relaxants), and ANS control. Regaining consciousness has to be accompanied by pain control, and it is important to ensure that the patient regains baseline cognitive function. Anesthesia machine equipment, drug administration, and airway related topics make up the rest of published manuscripts.

Perioperative goal-directed therapy - What is the evidence?

Perioperative goal-directed therapy aims at optimizing global hemodynamics during the perioperative period by titrating fluids, vasopressors, and/or inotropes to predefined hemodynamic goals. There is evidence on the benefit of perioperative goal-directed therapy, but its adoption into clinical practice is slow and incomprehensive. Current evidence indicates that treating patients according to perioperative goal-directed therapy protocols reduces morbidity and mortality, particularly in patients having high-risk surgery. Perioperative goal-directed therapy protocols need to be started early, should include vasoactive agents in addition to fluids, and should target blood flow related variables. Future promising developments in the field of perioperative goal-directed therapy include personalized hemodynamic management and closed-loop system management.

Intraoperative Transesophageal Echocardiography During Cardiovascular Surgery in China

OBJECTIVE

To perform a comprehensive nationwide survey of more than 90% of all cardiovascular hospitals in China to assess the current 2018 status of transesophageal echocardiography (TEE) equipment, operating physicians, education, impact on surgery, and reimbursement.

DESIGN

In this nationwide survey, 716 cardiovascular hospitals in mainland China were included. A 15-question electronic survey was sent to these hospitals and the data were received directly from the questionnaire website for analysis.

SETTING

Cardiovascular hospitals in mainland China.

PARTICIPANTS

Departments of anesthesiology in cardiovascular hospitals in mainland China.

INTERVENTIONS

Answer a 15-question survey.

MEASUREMENTS AND MAIN RESULTS

About 90% of hospitals have acquired machines to perform TEEs with most of the machines controlled by the ultrasound department. Anesthesiologists performed intraoperative TEEs in 45% of the hospitals, but only 15% of the hospitals have anesthesiologists who have met the basic TEE training requirements. Most anesthesiologists (68%) believed TEE significantly contributed to patient care during cardiovascular surgeries. The overwhelming majority of surveyed hospital staff (93%) stated that they were planning to continue or start intraoperative TEE examinations in the future.

CONCLUSION

Many hospitals in China have acquired equipment to perform intraoperative TEE examinations during cardiovascular surgeries. However, the number of anesthesiologists who can perform TEEs independently still is not adequate. Standardized trainings, a formal certification process, and governmental payment model changes must be provided to ensure high-quality TEE services and better surgical outcomes in China.

Advancing frontiers in anaesthesiology with laparoscopy

The introduction of laparoscopy in the surgeon's armamentarium was in fact a "revolution in the history of surgery". Since this technique involves insufflation of carbon dioxide it produces several pathophysiological changes which have to be understood by the anaesthesiologist who can modify the anaesthesia technique accordingly. Advantages of laparoscopy include reduced pain, small scars and early return to work. Certain complications specific to laparoscopic surgery are due to carboperitoneum and increased intra-abdominal pressure. Venous air embolism, although very rare, can be lethal if not managed promptly. Other complications include subcutaneous emphysema, haemodynamic compromise and arrhythmias. Although associated with minimal postoperative morbidity, postoperative pain, nausea and vomiting can be quite problematic. The limitations of laparoscopy have been overcome by the introduction of robotic surgery. There are important implications for the anaesthesiologist during robotic surgeries which have to be practiced accordingly. Robotic surgery has a learning curve for both the surgeon and the anaesthesiologist. The robot is bulky, and cannot be disengaged after docking. Therefore it is important that the anaesthetized patient remains immobile throughout surgery and anaesthesia is reversed only after the robot has been disengaged at the end of surgery. Advances in laparoscopy and robotic surgery have modified anaesthetic techniques too.

[High-tech medical care in surgical endocrinology]

The number of patients with endocrine system diseases increases annually. Widespread introduction of screening programs and improvement of laboratory and instrumental diagnostic is one of the most important causes for this. Treatment of patients with endocrine system diseases within the high-tech medical care leads to perform the unique surgical interventions. It increases survival and patients' life quality.

Doppler microembolic signals during cardiopulmonary bypass: Comparison of two membrane oxygenators

We undertook this study to evaluate the dependence of Doppler microembolic signal (MES) counts, detected during cardiopulmonary bypass, on the type of oxygenator used. A total of 90 patients, 71 men and 19 women, aged 60 +/- 10 years (mean +/- SD), undergoing elective cardiac surgery for coronary artery bypass grafting (one vessel, n = 6; two vessels, n = 24; three vessels, n = 33; four vessels, n = 9) or valve replacement (mitral valve, n = 2, aortic valve, n = 15, both valves, n = 1) were monitored with transcranial Doppler sonography during the complete surgical procedure. The surgical and anesthetic techniques were standardized in all patients, except for the type of membrane oxygenator used (COBE CML Duo, n = 55 or DIDECO D 703, n = 35). MES count was expressed as total number of MES detected in both middle cerebral arteries during cardiopulmonary bypass (CPB) and also as total MES number divided by the CPB duration in minutes (MES min(-1)). No significant differences in patients' age or sex and type and duration of operation were noted between the two groups. MES incidence while the patients were on cardiopulmonary bypass was 100%. MES counts during CPB were 309 (236-502) and 143 (86-233) for DIDECO and COBE oxygenators, respectively (p < 0.00001). MES min(-1) were also significantly higher in patients operated with DIDECO, as compared to COBE oxygenators (3.7 (2.4-5.6) versus 1.5 (1-2.4), respectively, p < 0.0001). Inter-observer variability was satisfactory (k = 0.72). Use of a DIDECO D 703 oxygenator resulted in significantly higher MES counts as compared to the COBE CML Duo oxygenator. The clinical relevance of this finding remains to be determined.

[Current status of intraoperative motor evoked potential monitoring: a questionnaire study]

BACKGROUND

Intraoperative motor evoked potential (MEP) monitoring has been used for the purpose of preventing neural complications in surgical treatments. There is little information about the current status of intraoperative MEP monitoring in Japan.

METHODS

The survey targeted anesthesia departments mainly of university hospitals throughout the country.

RESULTS

Answers were obtained from 60 institutions (a response rate of 68%). Intraoperative MEP has been monitored in 58 institutions. Intraoperative MEP monitoring in 35 institutions did not exceed 50 times per year. Especially during thoracoabdominal aortic aneurysm repair, frequency of MEP monitoring in 51 institutions was limited to 10 times per year. A few anesthesiologists were concerned with evaluation of MEP in craniotomy and spine surgery. In contrast, anesthesiologists in 15 institutions were responsible for evaluation of MEP during thoracoabdominal aortic aneurysm repair. Warning criteria of MEP and therapeutic strategies in case of critical MEP change differed by institution. Fifty four responders expected a guideline for clinical use of intraoperative MEP monitoring.

CONCLUSIONS

A clinical practice guideline for intraoperative MEP monitoring based on the information from previous investigations and a planned multicenter clinical study is necessary to enhance its utility.

Multimodal intracranial monitoring: implications for clinical practice

This article presents an overview of intracranial monitoring techniques during the perioperative and intensive care management of neurologic patients. Various regional and global brain monitors are available; some modalities are well established whereas others are new to the clinical arena and their indications are still being evaluated. Indications for monitoring are reviewed, modalities critically evaluated, and future directions identified.

Brain shift compensation and neurosurgical image fusion using intraoperative MRI: current status and future challenges

Navigation systems are commonly used in neurosurgical operating theaters. Generally, they either rely on the use of preoperative or intraoperative image data. Using preoperative image data, the phenomenon of brain shift contributes most to errors, in addition to various other sources of decreased reliability, such as image-related errors or registration inaccuracy. Updating navigation after intraoperative magnetic resonance imaging (iMRI) serves as immediate feedback on the surgical result and furthermore compensates for the effects of brain shift. Together with an integration of functional data in the navigation such as diffusion tensor imaging (DTI)-based fiber tracking or functional MRI, there is evidence that iMRI contributes to maximize extent of resection in glioma surgery with a preservation of neurological function. The following article summarizes the work flow and clinical impact of iMRI and functional navigation, as well as current problems and possible solutions.

[What is new regarding anaesthetic monitoring in the operating room?]

This paper critically reviews the new devices that can be used on the operating room to monitor the oxygenation and the haemodynamics of the child undergoing general anaesthesia.

Pulse pressure variation: where are we today?

In the present review we will describe and discuss the physiological and technological background necessary in understanding the dynamic parameters of fluid responsiveness and how they relate to recent softwares and algorithms' applications. We will also discuss the potential clinical applications of these parameters in the management of patients under general anesthesia and mechanical ventilation along with the potential improvements in the computational algorithms.

Intraoperative continuous monitoring of evoked facial nerve electromyograms in acoustic neuroma surgery

BACKGROUND

Preservation of facial nerve function is one of the most important goals in acoustic neuroma surgery. We have been using intraoperative continuous monitoring of evoked facial nerve electromyograms (EMGs) since 1997 in acoustic neuroma surgery. We therefore investigated surgically treated patients to clarify the usefulness of this monitoring, and to determine safety criteria for preserving facial nerve function.

METHODS

This intraoperative continuous monitoring of evoked facial nerve EMG is a method for checking the EMG evoked by continuous direct electrical stimulation of the facial nerve during tumor excision. The greatest advantage of this method is the ability to identify changes in EMG in real time. We retrospectively investigated 216 patients with surgically treated acoustic neuroma to identify correlations between parameters in this monitoring and postoperative facial nerve function immediately and 1 year after surgery.

RESULTS

In these patients, the functional preservation rate of the facial nerve (House and Brackmann grade 1 or 2 at 1 year after surgery) was 98.6% with a 98.2% mean tumor resection rate. Amplitude preservation ratio correlated significantly with facial nerve function both immediately and 1 year after surgery. To avoid severe facial nerve palsy, a warning criterion of amplitude preservation ratio >50% appears useful.

CONCLUSIONS

Postoperative course of facial nerve function appears predictable using intraoperative continuous monitoring of evoked facial nerve EMGs. This monitoring is useful to increase the tumor excision rate while avoiding severe postoperative facial nerve palsy in acoustic neuroma surgery.

Origins of intraoperative MRI

Neurosurgical diagnosis and intervention has evolved through improved neuroimaging, allowing better visualization of anatomy and pathology. This article discusses the various systems that have been designed over the last decade to meet the requirements of neurosurgical patients and opines on the potential future developments in the technology and application of intraoperative MRI. Because the greatest amount of experience with intraoperative MRI comes from its use in brain tumor resection, this article focuses on the origins of intraoperative MRI in relation to this field.

[The measurement of anesthetic depth]

Monitoring the depth of anesthesia (DOA) is essential for improving the quality of anesthesia and ensuring the patient's safety and rehabilitation. Monitoring DOA can increase the quality of anesthesia and the safety of operation, thus decreasing the complications caused by anesthesia. With the development of electronic and information technology, the researches for detecting DOA have made great progress. In this paper, the techniques for monitoring DOA are reviewed.

Factors influencing neurologic outcome after neonatal cardiopulmonary bypass: what we can and cannot control

Advances in cardiopulmonary bypass and surgical techniques have led to progress in the early repair of congenital heart defects in children. However, as increasing numbers survive their initial cardiac operation, an awareness is emerging that significant early and late neurologic morbidities continue to complicate otherwise successful operative repairs. Adverse neurologic outcomes after neonatal cardiac surgery are multifactorial and relate to both fixed and modifiable mechanisms. The purpose of this review is to (1) review mechanisms of brain injury after neonatal cardiopulmonary bypass, (2) examine risk factors, and (3) speculate on how investigations may improve our understanding of neurologic injury.

Electrophysiologic monitoring in neurosurgery

Electrophysiologic techniques have become common in the neurosurgical operating room. This article reviews the methods used for mapping neural structures or monitoring during surgery. Mapping methods allow identification of target structures for surgery, or for identifying structures to allow avoidance or plot safe pathways to deeper structures. Monitoring methods allow for surgery on nearby structures to warn of encroachment, thereby reducing unwanted injury.

Surgery for intramedullary spinal cord tumors: the role of intraoperative (neurophysiological) monitoring

In spite of advancements in neuro-imaging and microsurgical techniques, surgery for intramedullary spinal cord tumors (ISCT) remains a challenging task. The rationale for using intraoperative neurophysiological monitoring (IOM) is in keeping with the goal of maximizing tumor resection and minimizing neurological morbidity. For many years, before the advent of motor evoked potentials (MEPs), only somatosensory evoked potentials (SEPs) were monitored. However, SEPs are not aimed to reflect the functional integrity of motor pathways and, nowadays, the combined used of SEPs and MEPs in ISCT surgery is almost mandatory because of the possibility to selectively injury either the somatosensory or the motor pathways. This paper is aimed to review our perspective in the field of IOM during ISCT surgery and to discuss it in the light of other intraoperative neurophysiologic strategies that have recently appeared in the literature with regards to ISCT surgery. Besides standard cortical SEP monitoring after peripheral stimulation, both muscle (mMEPs) and epidural MEPs (D-wave) are monitored after transcranial electrical stimulation (TES). Given the dorsal approach to the spinal cord, SEPs must be monitored continuously during the incision of the dorsal midline. When the surgeon starts to work on the cleavage plane between tumor and spinal cord, attention must be paid to MEPs. During tumor removal, we alternatively monitor D-wave and mMEPs, sustaining the stimulation during the most critical steps of the procedure. D-waves, obtained through a single pulse TES technique, allow a semi-quantitative assessment of the functional integrity of the cortico-spinal tracts and represent the strongest predictor of motor outcome. Whenever evoked potentials deteriorate, temporarily stop surgery, warm saline irrigation and improved blood perfusion have proved useful for promoting recovery, Most of intraoperative neurophysiological derangements are reversible and therefore IOM is able to prevent more than merely predict neurological injury. In our opinion combining mMEPs and D-wave monitoring, when available, is the gold standard for ISCT surgery because it supports a more aggressive surgery in the attempt to achieve a complete tumor removal. If quantitative (threshold or waveform dependent) mMEPs criteria only are used to stop surgery, this likely impacts unfavorably on the rate of tumor removal.

Experience of 500 cases of neurophysiological monitoring in carotid endarterectomy

BACKGROUND

Experience with Intraoperative monitoring using neurophysiological and haemodynamic indices in 500 operations for carotid endarterectomy is reported.

METHODS

Transcranial Doppler technique (TCD), electroencephalogram (EEG) and bilateral median somatosensory evoked potentials (SEP) were performed. Latency and amplitude of SEP, spectral analysis of EEG signal and blood flow velocity in the medial cerebral artery (MCA) were continuously measured.

FINDINGS

After two consecutive drops of N20/P25 complex of more than 50%, a warning was given, and when the decrease continued, an the alarm raised. Abnormal EEG changes, if any, appeared after a significant decrease in the N20/P25 amplitude. A mean blood flow velocity drop below 40% of the reference value after cross clamping was rated as a significant warning event.A warning as a result of a decrease in N20/P25 amplitude occurred in 80 operations (16.0%), after an spectral edge frequency decrease in 2 cases (0.4%) and after a V(mean) decrease in 21 cases (4.2%). False negative results were experienced in 2 patients (0.4%). A shunt was inserted in 2.8% of the operations. The overall mortality/morbidity rate was 2.4%.

CONCLUSION

A decrease of more than 50% in the amplitude of the thalamocortical somatosensory evoked potential complex N20/P25 proved to be the most reliable warning of danger of ischaemia during carotid endarterectomy.

Intraoperative neurophysiological monitoring technology: recent advances and evolving uses

Intraoperative neurophysiological monitoring has evolved over the last 25 years to become an important component of many types of orthopedic and neurosurgical procedures. From its foundations in VIII cranial nerve surgeries and scoliosis corrections surgeries, intraoperative neurophysiological monitoring has expanded to incorporate nearly all spine procedures and many involving the brain and brainstem. Fundamental to this growth in the use of intraoperative neurophysiological monitoring has been the development of the technology used to perform the neurophysiological tests. Advancements in electronics and computer technology have resulted in significant improvements in the capacity, ease of use, quality and reliability of the equipment as well as the quality of and control over the acquired data. These technological advancements have resulted in remarkable improvements in not only the quality and availability of intraoperative neurophysiological monitoring, but also, as a consequence, patient care, and have arguably propelled the expansion of the use that intraoperative neurophysiological monitoring has seen over the last 10 years.

A prospective evaluation of the role for intraoperative x-ray in lumbar discectomy. Predictors of incorrect level exposure

BACKGROUND

Lumbar discectomy is among the most frequently performed procedures by spine surgeons. Among the potential difficulties encountered during this procedure, incorrect spinal level surgery remains a significant concern for surgeons and patients. Multiple groups have advocated the use of intraoperative x-ray to reduce the incidence of incorrect level surgery; however, this technique has not been prospectively evaluated.

METHODS

In an effort to determine the incidence of incorrect level exposure during lumbar discectomy and to define patient characteristics predictive of wrong level exposure, we examined 100 consecutive patients who underwent lumbar discectomy by a single surgeon. After exposure, the surgeon was asked to identify the level exposed, which was confirmed by intraoperative x-ray. Several patient characteristics were then examined by logistical regression to identify features predictive of a mismatch between level of exposure and level of pathology.

RESULTS

The study population was composed of 48 men and 52 women who were aged 18 to 83 years. Patient weights ranged from 105 to 410 lb. There were 51 patients who had pathology at the L5-S1 level; 44 patients, L4-L5; 3 patients, L3-L4; and 1 patient, L2-L3. Four patients had transitional vertebrae. The intended level was initially exposed in 85% of cases. Age and level of pathology (P < .05) were identified as factors predictive of a mismatch between intraoperative level of exposure and preoperative level of pathology.

CONCLUSIONS

Pathology above L5-S1 and patient age have been shown to reliably predict incorrect level exposure. Based upon the findings of this study, the routine use of intraoperative x-ray to confirm the level of exposure should be considered in all cases of lumbar discectomy.

[The changing role of intraoperative mammary frozen sections in breast cancer: comparison of data from East and West Germany before and after reunification]

The goal of the present study lies in the comparison of differently funded health care structures, with emphasis on certain aspects regarded to be essential for medical progress. For this purpose, mammary intraoperative frozen sections pooled from a total of 4163 intraoperative frozen sections obtained from representatively selected departments of pathology from East and West Germany before and after reunification were analysed comparatively. Our results clearly demonstrate a profound change in the role of intraoperative mammary frozen sections, with a predominantly diagnostic function in the former German Democratic Republic as a tool for histopathologically evaluating "questionable" mammary lesions. The use of such sections changed towards a predominantly therapeutic function during surgical treatment as a means of organ preservation after the German reunification.

Intraoperative Motor Evoked Potential Monitoring: Overview and Update

Amidst controversy about methodology and safety, intraoperative neurophysiology has entered a new era of increasingly routine transcranial and direct electrical brain stimulation for motor evoked potential (MEP) monitoring. Based on literature review and illustrative clinical experience, this tutorial aims to present a balanced overview for experienced practitioners, surgeons and anesthesiologists as well as those new to the field. It details the physiologic basis, indications and methodology of current MEP monitoring techniques, evaluates their safety, explores interpretive controversies and outlines some applications and results, including aortic aneurysm, intramedullary spinal cord tumor, spinal deformity, posterior fossa tumor, intracranial aneurysm and peri-rolandic brain surgeries. The many advances in motor system assessment achieved in the last two decades undoubtedly improve monitoring efficacy without unduly compromising safety. Future studies and experience will likely clarify existing controversies and bring further advances.

Multimodal protocol for awake craniotomy in language cortex tumour surgery

BACKGROUND

Intra-operative neurophysiological language mapping has become an established procedure in patients operated on for tumours in the area of the language cortex. Awake cranial surgery has specific risks and patients are exposed to an increased physical and mental stress. The aim of the study was to establish an algorithm that enables tailoring the neurosurgical and anaesthetic techniques to the individual patient.

METHOD

A total of 25 patients underwent awake craniotomy for intra-operative language mapping between 1999 and 2004. Following craniotomy under analgesia and sedation without rigid pin fixation of the head, cortical language mapping was performed in the fully co-operative patient. The results of functional magnetic resonance imaging and of cortical language mapping were incorporated into the 3D dataset for neuronavigation. Depending on the functional data and the individual operative risk tumour resection then proceeded either under conscious sedation with the option of subcortical language monitoring or under general anaesthesia.

FINDINGS

After cortical language mapping patients are assigned to one of four groups: BACC (Berlin awake craniotomy criteria) I-IV. BACC I (9 patients): adequate functional data+operative risk not increased-->tumour resection in the awake patient; BACC II (4 patients): limited functional data+operative risk not increased-->tumour resection in the awake patient with the option of language monitoring as needed; BACC III (9 patients): adequate functional data+increased operative risk-->tumour resection under general anaesthesia using functional navigation; BACC IV (3 patients): limited functional data+increased operative risk-->tumour resection in the awake patient with the option of language monitoring as needed. We observed less adverse events in group BACC III. No permanent deterioration of language function occurred in this series.

CONCLUSIONS

The multimodal protocol for awake craniotomy provides for tumour resection under general anaesthesia in selected patients using functional neuronavigation. Our experience with the algorithm suggests that it is a useful tool for preserving function in patients undergoing surgery of the language cortex while reducing the operative risk on an individual basis.

Brainstem auditory evoked potential monitoring: When is change in wave V significant?

BACKGROUND

The probability of hearing loss during cerebellopontine angle (CPA) surgery can be reduced by using brainstem auditory evoked potential (BAEP) intraoperative monitoring (IOM). A wave V latency prolongation of 1.0 milliseconds or amplitude decrement of greater than 50% is arbitrarily considered the point when damage to hearing occurs.

OBJECTIVE

To determine the accuracy of wave V changes in predicting hearing impairment.

METHODS

Patients undergoing BAEP IOM for surgery in the CPA region were evaluated. The greatest wave V latency and amplitude change was determined. Patients were divided into four groups depending on degree of change of wave V: Group 1 consisted of minimal change, whereas Group 4 was permanent loss of wave V. The frequency of hearing loss in each group was compared.

RESULTS

Data from 156 patients were reviewed. When all patients were analyzed, the frequency of hearing loss was not significantly different between the groups. When patients with CPA tumor were excluded, a significantly higher number of patients in Group 4 had hearing loss. Analysis of the patients with CPA tumor showed no difference in the frequency of hearing loss in any of the groups; even a large number (50%) of Group 1 patients had hearing impairment.

CONCLUSIONS

During brainstem auditory evoked potential intraoperative monitoring, the type of surgery is important when interpreting significance of changes of wave V. For non-cerebellopontine angle tumor surgery, hearing loss occurs usually only with permanent loss of wave V; much smaller changes may be important in cerebellopontine angle tumor surgery.

Cervical Myelopathy Due to OPLL

BACKGROUND

Concerning the relationship between morphology and clinical outcome, there have been many reports using computed tomography/myelography but not so many using axial magnetic resonance imaging (MRI) of the spinal cord. This is the first report to correlate axial cord image, intensity changes in MRI, and cord expansion pattern using intraoperative ultrasonography.

OBJECTIVE

The objectives were to correlate MRI studies, axial cord images/expansion, and changes in MRI intensity to see if there is a direct prognostic significance to these changes and to determine whether preoperative axial MRI images of the spinal cord predict recovery from compressive myelopathy.

METHODS

Posterior cervical decompressions with laminoplasty were performed in 44 patients with cervical myelopathy due to ossification of the posterior longitudinal ligament. On T2-weighted MR images, the cross-sectional shape of the cord at the level of maximal compression was categorized as boomerang, teardrop, or triangle. Additionally, with use of intraoperative ultrasonography, the expansion pattern of the cord that occurred intraoperatively was contrasted with that seen on postoperative MR images.

RESULTS

Clinical recovery rates were the worst for those with triangular, intermediate for those with boomerang, and the best for those with teardrop shape. Preoperative low T1 and high T2 signals were found in most cases with triangular cord configurations. Triangular cord configurations showed the least expansion among the three categorized spinal cords.

CONCLUSION

Patients with triangular deformity of the cord have atrophy as confirmed on MR studies where there is a low T1 and high T2 signal in the cord. Poor postoperative clinical recovery correlates with the lack of postoperative cord expansion on either MR or ultrasound evaluations. Those with either teardrop or boomerang deformities demonstrate a relatively good recovery rate.

Intracranial neuronavigation with intraoperative magnetic resonance imaging

PURPOSE OF REVIEW

This is an invited review regarding the use of intraoperative magnetic resonance imaging in the neurosurgical setting. The medical literature evaluating the intraoperative use of magnetic resonance imaging for neurosurgery has increased steadily since the implementation of this technique 10 years ago. The present review discusses recent findings and the current use of intraoperative magnetic resonance imaging in neurosurgery with special emphasis on the quality of available evidence.

RECENT FINDINGS

Intraoperative use of magnetic resonance imaging is a safe technique that enables the neurosurgeon to update data sets for navigational systems, to evaluate the extent of tumor resection and modify surgery if necessary, to guide instruments to the site of the lesion, and to evaluate the presence of intraoperative complications at the end of surgery. Although recent findings support the safety and efficacy of intraoperative magnetic resonance imaging for the above-mentioned purposes, there is no convincing evidence regarding its prognostic significance in the neurosurgical setting.

SUMMARY

Although the use of intraoperative magnetic resonance imaging in neurosurgery has increased significantly within the last 10 years, currently there are less than two dozen dedicated intraoperative units in the United States. The popularization of this technique depends on both economic justification and high-quality scientific evidence supporting its prognostic importance regarding patient outcome.

Motor evoked potential monitoring for spinal cord and brain stem surgery

Intraoperative Neurophysiology (ION) has established itself as one of the means by which modern neurosurgery can improve surgical results while minimizing morbidity. The advent of motor evoked potential (MEP) monitoring represents a landmark in this recent progress. ION consists of monitoring (the continuous "on-line" assessment of the functional integrity of neural pathways) and mapping (the functional identification and preservation of anatomically ambiguous nervous tissue) techniques. In this chapter we have attempted to critically review the evolution of MEP use during monitoring and mapping techniques for neurosurgical procedures in the brainstem and the spinal cord, providing the neurophysiological theoretical background and practical aspects of clinical applications. According to the experience from our and other groups involved in ION, we suggest the following: 1) ION is mandatory whenever neurological complications are expected as predicted by a known pathophysiological mechanism. It is therefore advisable to perform ION when dealing with brain stem and intramedullary spinal cord lesions. 2) MEP monitoring after transcranial electrical stimulation is today a feasible and reliable technique for use under general anesthesia. MEP monitoring is the most appropriate technique to assess the functional integrity of descending motor pathways in the brainstem and, foremost, in the spinal cord. 3) Mapping of the corticospinal tract at the level of the cerebral peduncle as well as mapping of the VII, IX-X and XII cranial nerve motor nuclei on the floor of the fourth ventricle is of great value with which to identify "safe entry zones" into the brainstem. 4) Other techniques, although safe and feasible, still lack rigorous validation in terms of prognostic value and correlation with the postoperative neurological outcome. These techniques include mapping of the corticospinal tract within the spinal cord and monitoring of the corticobulbar tracts. These techniques, however, are expected to open new perspectives in the near future.

Intraoperative auditory monitoring in vestibular schwannoma surgery: new trends

OBJECTIVE

To investigate the efficiency of a new method of brainstem auditory-evoked potential (BAEP) monitoring during complete vestibular schwannoma (VS) resection with attempted hearing preservation.

MATERIAL AND METHODS

Dedicated software providing near real-time recording was developed using a rejection strategy of artifacts based on spectral analysis. A small sample number (maximum 200) is required and results are obtained within 10 s. Fourteen consecutive patients with hearing class A operated on for VS, in an attempt to preserve hearing, participated in the investigation. Postoperatively, 7 patients (50%) had useful hearing (hearing class A, 4/14; hearing class B, 3/14) on the operated side. Seven patients (50%) were reduced to hearing class D.

RESULTS

Drilling of the internal auditory canal (IAC) and tumor removal at the lateral end of the IAC were identified as the two most critical steps for achieving hearing preservation. Intraoperative BAEP monitoring was sensitive in detecting auditory damage with useful feedback but its effectiveness in preventing irreversible hearing impairment was not demonstrated in this study.

CONCLUSION

Combined BAEP and direct auditory nerve monitoring using the same equipment will be performed in the future in an attempt to enhance the chances of preventing irreversible hearing damage, and possibly to improve the hearing outcome significantly.

Perioperative management and monitoring in anaesthesia

In recent years, several risk factors for adverse outcome in patients undergoing anaesthesia have been identified. Besides human errors, cardiovascular and respiratory complications are associated with substantial morbidity. Assessment of complications has promoted the introduction of basic physiological monitoring in clinical practice. Whether monitoring directly affects outcome is not proven; however, circumstantial evidence suggests that basic cardiorespiratory monitoring decreases the incidence of serious accidents. Prevention of hypothermia also reduces anaesthesia-related morbidity. Measurement of body temperature is mandatory, and active warming is a simple, effective technique to avoid hypothermia. Evidence is growing that patients with known or suspected coronary artery disease should be treated with beta blockers perioperatively. Whether the type of anaesthesia-ie, general or regional-is relevant to perioperative mortality remains unclear. In subgroups of patients at high risk, neuraxial anaesthesia reduces the rate of respiratory and cardiovascular complications.

Monitoring approaches in general anesthesia: a survey

The aim of this article is to give an overview of recent developments in the field of general anesthesia monitoring. We measure different physiological signals related to the functioning of several nervous systems. Using statistical or signal processing methods, monitors are derived and correlated to the dosage of anesthetic agents and to the status of the patient. Comparisons among existing monitors show that there is no one universal monitor applicable to all general anesthesia--each has its own characteristics and might be useful in particular clinical situations. Modeling of the underlying physiological mechanisms of the anesthesia may help for better understanding the interactions between anesthetic agents and nervous systems. Physiological-model-based general anesthesia monitoring and control can then be considered and optimized for each patient.

Intraoperative neurophysiological monitoring in pediatric neurosurgery: why, when, how?

INTRODUCTION

This review is primarily based on peer-reviewed scientific publications and on the authors' experience in the field of intraoperative neurophysiology. The purpose is a critical analysis of the role of intraoperative neurophysiological monitoring (INM) during various neurosurgical procedures, emphasizing the aspects that mainly concern the pediatric population. Original papers related to the field of intraoperative neurophysiology were collected using medline. INM consists in monitoring (continuous "on-line" assessment of the functional integrity of neural pathways) and mapping (functional identification and preservation of anatomically ambiguous nervous tissue) techniques. We attempted to delineate indications for intraoperative neurophysiological techniques according to their feasibility and reliability (specificity and sensitivity).

DISCUSSION AND CONCLUSIONS

In compiling this review, controversies about indications, methodologies and the usefulness of some INM techniques have surfaced. These discrepancies are often due to lack of familiarity with new techniques in groups from around the globe. Accordingly, internationally accepted guidelines for INM are still far from being established. Nevertheless, the studies reviewed provide sufficient evidence to enable us to make the following recommendations. (1) INM is mandatory whenever neurological complications are expected on the basis of a known pathophysiological mechanism. INM becomes optional when its role is limited to predicting postoperative outcome or it is used for purely research purposes. (2) INM should always be performed when any of the following are involved: supratentorial lesions in the central region and language-related cortex; brain stem tumors; intramedullary spinal cord tumors; conus-cauda equina tumors; rhizotomy for relief of spasticity; spina bifida with tethered cord. (3) Monitoring of motor evoked potentials (MEPs) is now a feasible and reliable technique that can be used under general anesthesia. MEP monitoring is the most appropriate technique to assess the functional integrity of descending motor pathways in the brain, the brain stem and, especially, the spinal cord. (4) Somatosensory evoked potential (SEP) monitoring is of value in assessment of the functional integrity of sensory pathways leading from the peripheral nerve, through the dorsal column and to the sensory cortex. SEPs cannot provide reliable information on the functional integrity of the motor system (for which MEPs should be used). (5) Monitoring of brain stem auditory evoked potentials remains a standard technique during surgery in the brain stem, the cerebellopontine angle, and the posterior fossa. (6) Mapping techniques (such as the phase reversal and the direct cortical/subcortical stimulation techniques) are invaluable and strongly recommended for brain surgery in eloquent cortex or along subcortical motor pathways. (7) Mapping of the motor nuclei of the VIIth, IXth-Xth and XIIth cranial nerves on the floor of the fourth ventricle is of great value in identification of "safe entry zones" into the brain stem. Techniques for mapping cranial nerves in the cerebellopontine angle and cauda equina have also been standardized. Other techniques, although safe and feasible, still lack a strong validation in terms of prognostic value and correlation with the postoperative neurological outcome. These techniques include monitoring of the bulbocavernosus reflex, monitoring of the corticobulbar tracts, and mapping of the dorsal columns. These techniques, however, are expected to open up new perspectives in the near future.

Intraoperative magnetic resonance imaging: considerations for the operating room of the future

Recent technological advances have made possible the introduction of the magnetic resonance imaging (MRI) system into the operating room to guide neurosurgical interventions. We review the possibilities and limitations associated with various open-configuration magnet designs, including systems from the Phillips, Siemens, General Electric, Odin and IMRIS designs. This technology has been shown to be a feasible adjunct to current neurosurgical management of intracranial brain tumors for both biopsy and resection procedures and shows significant potential applications for epilepsy surgery, spine surgery and for minimally invasive interventional techniques. Combined with other surgical planning modalities, intra-operative MRI scanners provide an evolutionary influence on the design of today's operating room.

Newer trends in monitoring: the esophageal Doppler monitor

The esophageal Doppler monitor is a recent development in hemodynamic monitoring that is used for surgical patients. It is relatively noninvasive and measures descending aortic blood flow by the Doppler effect. A comparison of this new monitor with the pulmonary artery catheter is cited numerous times throughout the literature and overall correlates well. Studies of the esophageal Doppler monitor show it to be a safe addition to operating room monitors for use by the anesthetist.