Dexmedetomidine Does Not Affect Evoked Potentials During Spine Surgery.

BACKGROUND: The effect of dexmedetomidine on evoked potentials (EPs) has not been elucidated. We aimed to investigate the effect of dexmedetomidine on somatosensory, motor, and visual EPs. METHODS: After IRB approval, 40 adult patients scheduled for elective spine surgery using total IV anesthesia with propofol and remifentanil were randomly assigned to receive either dexmedetomidine (n = 20) or placebo (n = 20) in a double-blind, placebo-controlled trial. After obtaining informed consent, positioning, and baseline EPs recording, patients were randomly assigned to either IV dexmedetomidine 0.6 µg/kg infused over 10 minutes, followed by 0.6 µg/kg/h, or a corresponding volume of IV normal saline (placebo). EP measures at 60 ± 30 minutes after initiation of study drug were defined as T1 and at 150 ± 30 minutes were defined as T2. Changes from baseline to T1 (primary end point) and from baseline to T2 (secondary end point) in EP latencies (milliseconds) and amplitudes (microvolts) were compared between groups. Data presented as mean ± SD (95% confidence interval). RESULTS: Data from 40 patients (dexmedetomidine: n = 20; age, 54 ± 3 years; 10 males; placebo: n = 20; age, 52 ± 2 years; 5 males) were analyzed. There was no difference between dexmedetomidine versus placebo groups in primary end points: change of somatosensory EPs at T1, latency: 0.01 ± 1.3 (-0.64, 0.65) vs 0.01 ± 1.3 (-0.64, 0.65), P = 0.43 (-1.24, 0.45); amplitude: 0.03 ± 0.14 (-0.06, 0.02) vs -0.01 ± 0.13 (-0.07, 0.05), P = 0.76 (-0.074, 0.1); motor EPs amplitude at T1: 65.1 ± 194.8 (-35, 165; n = 18) vs 109.2 ± 241.4 (-24, 243; n = 16), P = 0.57 (-113.5, 241.57); visual EPs at T1 (right eye), amplitude: 2.3 ± 3.6 (-0.4, 5.1; n = 11) vs 0.3 ± 6.0 (-3.3, 3.9; n = 16), P = 0.38 (-6.7, 2.6); latency N1: 2.3 ± 3.6 (-0.4, 5.1) vs 0.3 ± 6.0 (-3.3, 3.9), P = 0.38 (-6.7, 2.6); latency P1: -1.6 ± 13.4 (-11.9, 8.7) vs -1.4 ± 8.1 (-6.3, 3.5), P = 0.97 (-9.3, 9.7) or secondary end points. There were no differences between right and left visual EPs either at T1 or at T2. CONCLUSIONS: In clinically relevant doses, dexmedetomidine as an adjunct to total IV anesthesia does not seem to alter EPs and therefore can be safely used during surgeries requiring monitoring of EPs.

A comparison of the effects of desflurane versus propofol on transcranial motor-evoked potentials in pediatric patients.

PURPOSE: The aim was to compare the effects of propofol and desflurane anesthesia on transcranial motor evoked potentials (MEPs) from pediatric patients undergoing surgery for spinal deformities. METHODS: Desflurane and propofol cohorts (25 patients each) were obtained retrospectively and matched for patient characteristics and surgical approach. MEPs from the thenar eminence and abductor hallucis were compared during maintenance anesthesia on desflurane (0.6-0.8 MAC) or propofol infusion (150-300 µg/kg/min). MEP amplitudes and durations were obtained for successive 30-min intervals for 150 min, beginning 60 min after maintenance anesthesia. RESULTS: Mean peak to peak amplitudes of MEPs under desflurane anesthesia from the thenar eminence (419 µV) and abductor hallucis (386 µv) were not significantly different from those under propofol (608 µV, 343 µV, thenar, and abductor hallucis, respectively). Stimulation was greater by 42 V and 136 mA, and trains were slightly longer in the desflurane compared to the propofol group (p < 0.05). Most MEP amplitudes for the desflurane and propofol cohorts remained the same or increased (71 % of cases) when those after 150 min were compared to those in the first 30-min interval. CONCLUSIONS: MEPs with good amplitudes were obtained under desflurane only anesthesia that were comparable to propofol only anesthesia in pediatric patients during surgery for spinal deformities. There was no evidence for anesthetic fade over the time period examined. When used by itself, desflurane can be considered a viable alternative to propofol anesthesia.

Alternative sites for intraoperative monitoring of cranial nerves X and XII during intracranial surgeries.

During intracranial surgeries, cranial nerve (CN) X is most commonly monitored with electromyographic endotracheal tubes. Electrodes on these endotracheal tubes may be displaced from the vocal folds during positioning, and there is a learning curve for their correct placement. Cranial nerve XII is most commonly monitored with electrodes in the dorsum of the tongue, which are also prone to displacement because of their proximity to the endotracheal tube. A retrospective review was conducted of a consecutive series of 83 skull base surgeries using alternative sites for monitoring CN X and XII. On-going (spontaneous) and evoked electromyography (EMG) were obtained from the cricothyroid muscle for CN X and submental genioglossus for CN XII. Stimulation of CN X or XII evoked specific compound motor action potentials from these muscles, and well-defined on-going EMG was observed during tumor resection in the vicinity of CN X and XII. Volume-conducted responses from the adjacent platysma muscle during CN VII stimulation were identified by concomitant responses from the orbicularis oris and oculi. In conclusion, during skull base surgeries, CN X may be monitored with electrodes in the cricothyroid muscle and CN XII with electrodes in the submental genioglossus. These alternative sites are less prone to displacement of electrodes compared with the more commonly used EMG endotracheal tube and electrodes in the dorsum of the tongue. The cricothyroid muscle should not be used when the recurrent laryngeal nerve is at risk.

Effects of anesthetic regimens and other confounding factors affecting the interpretation of motor evoked potentials during pediatric spine surgery.

Children undergoing corrective spine surgery are at risk of serious neurologic injury. Monitoring transcranial electric motor evoked potentials (TCeMEPs) during these procedures may identify and help prevent injury to motor pathways. The difficulty in obtaining consistent motor evoked potential (MEP) responses during pediatric spine surgery can result in part to the suppression of evoked responses caused by volatile inhalational anesthetics, elevated levels of propofol, and/or physiologic variables. Data obtained from 140 pediatric patients who underwent spine surgery with MEP monitoring were retrospectively analyzed and evaluated for age and anesthetic effects on stimulation variables. MEPs acquired under inhalational anesthetic agents required greater stimulation compared to intravenous propofol anesthesia. Additionally, the responses were more variable when inhalational agents were used. These effects were more prominent in younger age patients. The number of alerts of MEP loss or reduction related to anesthetic levels or blood pressure changes was higher under inhalational agents.

Assessing the effects of subthalamic nucleus stimulation on gait and mobility in people with Parkinson disease.

PURPOSE: To determine the effects of unilateral and bilateral subthalamic nucleus (STN) stimulation on gait and mobility in persons with Parkinson disease (PD). METHOD: We examined eight individuals with advanced PD who underwent staged stimulator implantation surgeries. Gait and mobility were assessed in the medication-on state with a variety of clinical and laboratory measures (Unified Parkinson Disease Rating Scale items, Timed Up and Go Test, gait speed) at three time points: prior to surgery, after the first surgery (unilateral stimulation) and after the second surgery (bilateral stimulation). RESULTS: Despite overall improvements in motor function and reduction of dyskinesia, there were no significant group effects of unilateral or bilateral stimulation on gait and mobility compared to pre-surgical function. However, there were clinically meaningful changes, both improvements and declines, at the individual level. CONCLUSIONS: Because of the consequences of gait deficits and mobility limitations for people with PD, future research should examine the effects of STN stimulation on gait in the medication-on state using sensitive and specific measures such as gait speed. Accurate assessment of gait changes is necessary to improve the evaluation of STN effects and the prediction of individuals in need of rehabilitation services to manage gait and mobility deficits.

Spinal accessory neuropathy after deep brain stimulation for Parkinson's disease.

We report a man with Parkinson's disease who developed right spinal accessory neuropathy after right subthalamic nucleus deep brain stimulator and infraclavicular pulse generator implantation. He complained of right shoulder pain and weakness in the post-operative period. He was subsequently diagnosed with a right spinal accessory nerve injury, confirmed by neuromuscular electrodiagnostic studies - electromyography (EMG) and nerve conduction (NC) -, possibly caused by a stretch injury to the nerve at the time of creation of the subcutaneous tunnel for placement of the extension lead of the deep brain stimulator system. However, he had near complete clinical resolution of the spinal accessory neuropathy within nine months after surgery. As a result of this complication, we now map the spinal accessory nerve electrophysiologically during deep brain stimulation surgery.

Staged unilateral versus bilateral subthalamic nucleus stimulator implantation in Parkinson disease.

In 17 consecutive patients with Parkinson disease (PD), bilateral subthalamic nucleus (STN) stimulators were implanted during staged surgeries. The Unified Parkinson Disease Rating Scale (UPDRS) and the Dyskinesia Disability Scale were completed both off and on medication prior to any surgery and also OFF and ON stimulation after each surgery. On-medication UPDRS activities of daily living (ADL) and motor examination scores changed little with unilateral or bilateral stimulation. Off-medication UPDRS motor examination scores improved to similar degrees after each staged STN electrode implantation. Most of the improvements in off-medication ADL scores, dyskinesia scores, complications of therapy, and medication dose reduction occurred after unilateral STN stimulation with smaller improvements after the second operation.

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.

Clinical experience with dexmedetomidine for implantation of deep brain stimulators in Parkinson's disease.

The pharmacologic profile of the alpha-2 agonist dexmedetomidine (Dex) suggests that it may be an ideal sedative drug for deep brain stimulator (DBS) implantation. We performed a retrospective chart review of anesthesia records of patients who underwent DBS implantation from 2001 to 2004. In 2003, a clinical protocol with Dex sedation for DBS implantation was initiated. Demographic data, use of antihypertensive medication, and duration of mapping were compared between patients who received Dex (11 patients/13 procedures) and patients who did not receive any sedation (controls: 8 patients/9 procedures). There were no differences in severity of illness between the two groups. Dex provided patient comfort and surgical satisfaction with mapping in all cases, and significantly reduced the use of antihypertensive medication (54% in the Dex group, versus 100% in controls, P = 0.048). In DBS implantation, sedation with Dex did not interfere with electrophysiologic mapping, and provided hemodynamic stability and patient comfort. Routine use of Dex in these procedures may be indicated.

Gait changes in response to subthalamic nucleus stimulation in people with Parkinson disease: a case series report.

BACKGROUND AND PURPOSE: For individuals with advanced Parkinson disease (PD), stimulation of the subthalamic nucleus (STN) reduces tremor, rigidity, and bradykinesia, but the effects of stimulation on gait and mobility are not fully understood. The purpose of this paper is to describe the effects of unilateral and bilateral STN stimulation on gait following staged stimulator implantations in a series of individuals with PD. CASE DESCRIPTIONS: Participants were 6 individuals with PD who underwent staged stimulator implantation surgeries. The effects of stimulation on gait were assessed in the optimally medicated state using items from the Unified Parkinson's Disease Rating Scale (UPDRS) related to gait and self-reported mobility, time to complete the Timed Up and Go (TUG) test, and quantitative gait analysis. Gait was evaluated with stimulation turned off and with stimulation turned on after unilateral stimulator implantation and again after implantation of the second stimulator. OUTCOMES: Variable effects of unilateral and bilateral STN stimulation on gait were observed on UPDRS self-reported mobility, TUG time, and gait velocity, but changes were not detected using the UPDRS gait item. Minimal gait changes, either positive or negative, were detected with unilateral stimulation. With bilateral stimulation, gait improved for 3 individuals but worsened for the other 3 individuals. DISCUSSION: The ability to detect changes in gait after STN stimulation using the UPDRS gait item was limited, but variable effects were detected by self-report, TUG time, and gait velocity. For half of the individuals studied, bilateral stimulation improved these measures, but gait worsened for the remaining individuals. Future research is needed to better understand factors that influence the effect of STN stimulation on walking, and assessment of gait changes in people with PD should include self-report and performance-based measures, such as the TUG test or gait velocity.

Unilateral subthalamic nucleus deep brain stimulation contralateral to thalamic stimulation in Parkinson disease.

The effects of unilateral subthalamic nucleus (STN) stimulation contralateral to thalamic stimulation in Parkinson disease (PD) have not been previously reported. We are reporting a patient who developed left arm tremor in 1994, at age 62, as her first PD symptom. She underwent right thalamic DBS surgery in 1999 that resulted in complete resolution of left arm tremor. Her PD symptoms progressed and she developed severe motor fluctuations and disabling dyskinesias. In 2003, she underwent left STN electrode implantation. Left STN stimulation improved contralateral motor scores in the medication OFF state, and allowed for reduced medication doses and less dyskinesia. However, there was no significant improvement in activities of daily living (ADL), motor scores in the medication ON state, gait, or postural stability.

Deep brain stimulation in a patient on immunosuppressive therapy after renal transplant.

We performed thalamic deep brain stimulation (DBS) surgery to treat severe essential tremor in a 36 year-old woman who had undergone cadaveric renal transplant four years earlier. She was receiving chronic immunosuppressive therapy. Post-operative healing was normal and there have been no infections of the DBS hardware. There were no peri-operative complications and no rejection of the transplanted kidney. She remains on the same systemic immunosuppressive agents as pre-operatively: prednisone, cyclosporine, and mycophenolate mofetil (CellCept). DBS surgery may be safely performed in carefully selected patients on systemic immunosuppression after renal transplant.

Mechanical failure of the electrode wire in deep brain stimulation.

The feasibility and efficacy of deep brain stimulation (DBS) has offered new possibilities for treatment of movement disorders. Mechanical failure of the DBS system is a potential complication. Here we report five patients who presented with mechanical failure of the DBS system. Radiographs of the skull and cervical spine were analyzed for disruptions. Seven instances of lead breakage near the connection of the DBS electrode with the extension wire were identified. In one patient this was in the paramastoid area over the skull, while in all others were in the supraclavicular location. The patients consisted of three men and two women ranging in age from 24 to 78 (at the time of first operation), one person suffering three breakages. The length of spanned time from implantation to presentation ranged from 8 to 32 months. Palpation of the electrode lead wire in the neck for breakage proved unreliable. Radiography localized the site of breakage in all but one patient who required intraoperative exploration, which revealed that although the lead wire was disrupted, the two ends remained in contact. The fact that all breakages occurred near the connection wire suggests that to-and-fro motion of the DBS electrode with repeated head turning leads to fatigue and eventual disruption.

Electrophysiologic intraoperative monitoring for spine procedures.

The advent of equipment capable of performing SEPs, MEPs, and EMG in a multiplexed manner and in a timely fashion brings a new level of monitoring that far exceeds the previous basic monitoring done with SEPs only. Whether this more comprehensive monitoring will result in greater protection of the nervous system awaits future analysis. In any event, monitoring of the spinal cord with SEPs is an accepted standard of care for cases that place the spinal cord at risk. Likewise, nerve root monitoring with EMG is a widely practiced form of monitoring and shows great benefit. MEPs and reflex monitoring, which address the descending pathways and the interneuronal connections, is efficacious in detecting abnormalities that may be missed by SEPs.

Bilateral subthalamic nucleus stimulation after bilateral pallidotomies in a patient with advanced Parkinson's disease.

A 54-year-old man with advanced Parkinson's disease (PD) presented to our institution in early 2000. He had undergone a right pallidotomy in 1994, a left pallidotomy in 1996, and bilateral subthalamic nucleus (STN) electrode implants in 1999. The patient had cervical myelopathy for which he had undergone neck surgery in 1998. We used the Unified Parkinson's Disease Rating Scale (UPDRS) to evaluate motor performance in four states: combinations of stimulation OFF or ON and medication OFF or ON. There was no significant change in motor UPDRS scores with STN stimulation or with medications. Multiple attempts to optimize stimulation parameters and medication dosages did not result in significant and sustained improvement in activities of daily living or motor performance. To our knowledge, this is the first reported case of bilateral STN stimulation after bilateral pallidotomies. The presence of cervical myelopathy and the limited response to anti-Parkinson medications in this patient underscores the importance of patient selection for functional neurosurgery in PD.