Biomedical subjects
Publications and source records attributed to J Schramm.
Spinal evoked potentials to sciatic nerve stimulation were recorded with epidural electrodes over the dorsal columns. A comparison with potentials to dorsal column stimulation disclosed differences in the typical segmental variation in regard to wave form, amplitude, spinal conduction velocity and conduction time that could be important in neuromonitoring.
Flash-evoked visual potentials (VEPs) recorded from the scalp were used in a series of 35 patients with tumors along the visual pathway: 3 orbital tumors, 25 perisellar tumors, 4 intraventricular tumors, and 3 occipital lesions. Preoperatively, various combinations of impaired visual fields and visual acuity were observed in over 90% of the patients. A postoperative decrease in visual function was observed in 3 cases. Of the 25 perisellar lesions, 13 were operated through a standard frontotemporal craniotomy and 12 were operated through a transnasal-transsphenoidal approach. VEPs were highly susceptible to volatile anesthetics, and there was a significant incidence of spontaneous latency increases and amplitude decreases in a large number of patients. There was an unacceptably high number of cases with significant VEP alteration occurring without concomitant visual function change. During trepanation or the transnasal approach, a reversible potential loss was observed in 11 patients, a profoundly altered wave form was seen in 8 cases, and a loss of single peaks was observed in 15 patients. During dissection of the tumor, a reversible potential loss or a potential with unidentifiable peaks was found in 25 cases; however, the VEPs recovered during closure or in the recovery room. There was no correlation between intraoperative VEP changes and the postoperative changes in visual function. In only 1 patient with an insignificant postoperative decrease in visual acuity from 0.4 to 0.3 was there a concomitant intraoperative potential loss. The major conclusion of our findings is that light-emitting diode flash-evoked VEPs demonstrate intraoperative changes that appear too early and too prominently to be caused solely by manipulation of the optic pathways.(ABSTRACT TRUNCATED AT 250 WORDS)
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The use of evoked potential recording is commonly employed for monitoring peripheral and central sensory functions during neurosurgical procedures. However, the neuronal structures studied must not be changed by the anesthetic agents used. In this connection, the influence of two anesthetics, fentanyl and enflurane, on evoked potentials was investigated under basic anesthesia. A total of 60 patients undergoing lumbar disc removal were included in the study. Somatosensory (SEP), auditory (AEP), and visual (VEP) evoked potentials were each recorded in 20 patients the day before operation. Basic anesthesia was induced with flunitrazepam, nitrous oxide, and pancuronium bromide. Following induction, recordings of evoked potentials were again made. One half of each group of 20 patients received increasing doses of fentanyl (1.8, 3.6, and 7.2 micrograms/kg in the somatosensory and auditory groups; 4.0 and 8.0 micrograms/kg in the visual group). The other half was given increasing inspiratory concentrations of enflurane (0.5, 1.0, and 1.5 vol.%). At each level of anesthesia, SEPs, AEPs or VEPs were recorded. As compared with preoperative recordings, post-stimulus latencies were virtually unaffected by the basic anesthesia. Fentanyl caused little increase in the latencies of middle-latency-SEPs and of peak P2 of the VEPs. With enflurane, however, the latencies of the SEPs were dose-dependently prolonged, in particular those of the later components (P25 to N55). The same was true for the peak P2 in the VEPs. AEPs were not changed at all. From the results it can be concluded that enflurane, but not fentanyl, impairs impulse conduction in central synaptic pathways.(ABSTRACT TRUNCATED AT 250 WORDS)
Our recent experience stimulated a review of selective rhizotomies for the alleviation of localized pain. Three patients with postoperative neuralgia in the inguinal region and two with neoplastic root compression were treated. Results were good and long-lasting in two cases, moderate in two and poor in one case. The relief appeared to better, the more clearly the pain was localized. In lesions distal to the spinal root it is necessary to undertake selective paravertebral root blocks with local anaesthetics. Experimental data are discussed that help in an understanding of pain recurrence after rhizotomy.
A total of 50 patients with chronic pain syndromes were selected for treatment with spinal cord stimulation. Correct positioning of electrodes was obtained in 44 patients, leading to an initial alleviation of pain in 25 patients. In 6 patients, electrodes (though still effective in 4) had to be removed because of surgical complications within the first 5 months of use. Only 8 patients had at least some beneficial effect lasting for more than 3 years. The long-term results in patients with more severe psychological disturbances were no worse than those of the other patients.
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The case of a cystic craniopharyngioma in a young patient, in which the tumor extended in the parasellar and retrosellar region down to the left cerebellopontine angle, is described. The postoperative reversibility of alterations in the acoustic-evoked brainstem responses after repeated surgical intervention and refilling of the cyst is described. The correlations between clinical and CT findings and the repeated alterations in the evoked responses are presented. The evoked responses were instrumental in following the postoperative course and timing CT controls. It is stressed that alterations in evoked responses were used as a reliable indication to evacuate cyst fluid via a Rickham-reservoir, although hearing was still intact, thus keeping the number of repeated CT scans lower.
A review of current techniques and results of monitoring spinal cord function by the intraoperative testing of somatosensory evoked potentials is given. The criteria for an ideal monitoring method are defined: (1) potential alterations occur before the lesion is irreversible, (2) monitoring itself does not harm the patient, (3) there are no false-positive or false-negative results, (4) warning criteria are defined by objective and quantifiable parameters. In recording and stimulation, two different approaches are applied: cortical or spinal recording and peripheral or spinal stimulation. Spinal stimulation techniques are considered more invasive, but an averaged potential is obtained quicker and more reliably by spinal methods. Failure rates in establishing useful monitoring procedures vary between 2.85 and 5%. The N2O-analgesic-relaxant-type of anesthesia is recommended. A precise definition of criteria indicating spinal cord damage has been difficult because of the natural variability of intraoperative evoked potentials. Wide ranges of physiologic, anesthesiologic, and technical and surgical factors have been found to influence intraoperative potential monitoring adversely. The so-called warning criteria drawn from evoked potential changes have so far been set arbitrarily: amplitude reductions of 30-50% for several recordings or at least 15 minutes have mostly been used. It has become clear, however, that warning criteria should be different for healthy or impaired spinal cord function and for cortical and spinal recordings. The value of a lesion-specific spinal cord potential for monitoring remains to be clarified. SEPs are sensitive for demonstrating ischemic changes to the spinal cord, but the limited experience with these lesions does not allow firm conclusions regarding the reversibility of clinical and evoked potential changes in spinal cord ischemia in man. The limited experience with multilevel recording, i.e., simultaneously recording at spinal and cortical level, indicates that epidural recordings are less variable and less failure-prone than cortical recording. Simultaneous multilevel recording also gives more information and allows easier recognition of false-positive or false-negative results. Poor preoperative SEP nearly always preclude useful monitoring. The results obtained so far point out areas where further development is necessary in order to increase the efficacy of this method. Major unsolved problems are (1) definition of warning criteria, (2) incidence of false-positive and false-negative findings, and (3) improvement of data acquisition.(ABSTRACT TRUNCATED AT 400 WORDS)
From a series of 35 cases with intraoperative monitoring of acoustic evoked brainstem responses 4 cases with cerebellopontine angle surgery are presented in detail. The aim of neuromonitoring is to provide the surgeon with an additional instrument to assess the functional state of the hearing pathway with objective neurophysiological criteria during dissection near the eighth nerve and brainstem. Thus, a near total loss of potential during a neurovascular decompression of the trigeminal nerve could be reversed by modifying the surgical procedure. In 2 cases of acoustic neurinoma with preserved wave I this peak was obtainable throughout the procedure with a good postoperative result. Transient amplitude attenuation and latency increase was seen with a meningioma, which normalized before the end of operation with good postoperative hearing and brain-stem function. The relationship between intraoperative BAEP changes and postoperative brain-stem and eighth nerve function, and the value of neuromonitoring are discussed with regard to surgery around the internal auditory meatus and the eighth nerve.
Cortical and spinal evoked potentials were used to monitor the effect of experimental chronic cord compression in cats. An implantable compression screw made it possible to maintain the animals unrestrained. The mean compression period was 10 weeks (maximum 16.5 weeks). Compression was increased by stepwise tightening of the screw at intervals of 4 to 7 days under ketamine anesthesia. Evoked potentials were monitored before and after each compression step with repeated recordings, and were analyzed in terms of alterations in amplitude, latency, and waveform. Amplitude response curves were plotted where the amount of compression at each recording was expressed as a percentage of total compression. Changes in spinal evoked potentials occurred rather early (mean 36% of total compression), while obvious cortical evoked potential changes appeared rather late (mean 91% of total compression). Neurological alterations appeared later than alterations in spinal evoked response but prior to alterations in cortical evoked response. Thus, alterations in cortical somatosensory evoked potentials in the presence of chronic spinal compression indicate a severe degree of compression and do not seem to be of diagnostic value in the early detection of chronic spinal cord compression. It is suggested that the monitoring of spinal rather than cortical evoked responses would be more useful in locating and detecting chronic compression spinal cord damage.
Averaged somatosensory evoked potentials from the epidural space in response to sciatic nerve stimulation were recorded in bipolar and common reference mode in cats following various types of injury. An investigation was conducted on the development and properties of the spinal evoked response recorded from the center of the injury site, designated here as the "spinal cord evoked injury potential." Typically it is a two-peak monophasic positive potential, approximately 40 msec in duration, with a slight negative afterwave. With increasing distance from the site of injury, its amplitude rapidly decreases, whereas latency remains constant. The common reference recording technique resulted in an earlier and better demonstration of the evoked injury potential, especially when it was transitory or incomplete. When impairment of conduction developed gradually, the evoked injury potential developed gradually too. In serial recordings along the spinal cord axis, the transition from a normal triphasic to a monophasic evoked injury potential allowed a precise localization of the lesion. These data suggest that the diagnostic value of intraoperative spinal cord monitoring may be increased by adopting a technique that incorporates several epidural recordings with a common reference recording technique. The spinal cord evoked injury potential seems to be a more sensitive indicator of spinal cord injury than the cortical evoked potential. The findings are discussed in the light of the presently developing spinal cord monitoring techniques.
Seven cases of spinal epidural haematoma occurred in a series of 2,500 neurosurgical procedures. Five of these seven cases were non-traumatic in origin. In four cases the bleeding could be ascribed to various types of vascular malformations. The clinical and histological features are described, and the relevance of these findings for surgical management is discussed.
An experimental technique of chronic spinal compression combined with chronic implantation of cortical and spinal electrodes for the measurement of evoked potentials in cats is presented. This technique has the advantages of 1) requiring only a relatively simple dorsal access, 2) being applicable to the entire spinal cord, 3) permitting simple external control of compression speed and duration, and 4) allowing unhindered observation of motor behaviour in the unrestricted animal.