Biomedical subjects
Publications and source records attributed to J Schramm.
Report on three hydrocephalic, shunt dependent children, who became blind due to shunt malfunction and rapidly decreased intracranial pressure. They regained vision several days (one case) or several months (2 cases) after shunt revision. The related literature is reviewed and possible pathophysiological mechanisms are discussed.
To determine the role of the histamine H3-receptor on basophils, different specific H3-antagonists were investigated. Incubation of washed leukocytes with N alpha-acylated histamine-derivatives (N alpha-ahd) induced elevated histamine levels. This process turned out to be dependent on dose, time and temperature, but independent of Ca2+ and Mg2+ ions. IgE-mediated histamine release was not modulated. [3H]-L-histidine was not decarboxylated into [3H]-histamine in spite of the observed histamine increase. Highly purified basophils did not show any histamine elevation but purified neutrophils and eosinophils were found to have increased histamine levels even after disintegration and subsequent incubation with N alpha-ahd. It seems that the increased histamine levels result from the cleavage of the applied histamine amides. Other potent H3-antagonists (e.g. thioperamide) neither produced increased histamine levels nor influenced IgE-mediated release from basophil leukocytes. The existence of H3-receptors on human basophils therefore seems unlikely.
In summary, our results suggest that flash VEP monitoring is not specific for visual acuity and has not proved helpful as an intraoperative warning system. The future challenge will be to devise a method which activates only those fibers specific to visual acuity and which provides reproducible and reliable information quickly enough that adjustments in patient management can be made.
Somatosensory evoked potentials (SEPs) were monitored during 113 operations for the clipping of 134 cerebral aneurysms. Changes in peak latency and amplitude of early cortical SEP as well as central conduction time were evaluated. In 58 cases surgical occlusion of arterial vessels or other events occurred, and in 17 of these cases such events were associated with SEP changes or loss. Arterial occlusions resulted from temporary clipping of a feeding blood vessel (22), accidental clipping of a vessel (12), and intentional permanent vessel occlusion (8). A total SEP loss was seen in 2 cases of accidental vessel occlusion and in 6 cases of temporary vessel clipping. Significant SEP changes were found in 6 patients with temporary clipping, and once each with retraction of the cerebellum, retraction of the middle cerebral artery, and after intentional permanent vessel occlusion. Response to these changes included reapplication of aneurysm clips, repositioning of retractors, or removal of temporary clips. Stable SEP signals during 13 cases allowed the surgeon to proceed with the surgical course. Despite the limitations of SEP monitoring in certain anatomical locations, it has been found to be helpful in the operative management of some cases such as multilobed aneurysms of the middle cerebral artery, giant aneurysms, trapping procedures, and procedures requiring temporary vessel occlusion.
An 11-month-old boy was admitted for evaluation of drowsiness, vomiting, and convulsions. Computerized tomography showed subarachnoid blood in the left sylvian fissure and a small intracerebral hematoma in the temporal lobe. Angiography revealed several aneurysms of the left middle cerebral artery (MCA). During surgery, 13 aneurysms were found arising from one main branch of the left MCA, and this segment of the MCA was trapped. Somatosensory evoked potentials did not show any change during surgery. The diseased arterial segment was examined histologically and the pathogenetic aspects of the case are discussed. Control angiography 6 months later excluded systemic disease or other aneurysms. The rarity of such lesions in childhood and their successful surgical treatment are discussed briefly.
The intraventricular administration of morphine results in lesser systemic side effects, with an extremely satisfactorily pain relief going along with it (2, 5, 6). The subcutaneous pump which administers morphine intraventricularly is an interesting, non-destructive alternative of medium-term pain therapy for patients suffering from incurable pain caused by a malignant tumor in the oropharyngeal region. The morphine pump even makes it possible to go through terminal stages of the malignant disease well-relieved and in the familiar environment at home.
In 135 cases of posterior fossa surgery almost exclusively in the cerebellopontine angle (CPA) intraoperative monitoring of brain-stem acoustic evoked potentials (BAEP) and partly somatosensory evoked potentials (SEP) was performed. The series consisted of 20 microvascular decompressions, 63 acoustic neurinomas, 7 vascular lesions and 45 other space occupying lesions, mostly in the CPA. BAEP monitoring alone was employed in 76 cases, combined BAEP and SEP monitoring less frequently. The technique of anaesthesia and intraoperative monitoring is presented in detail including an analysis of technical problems (17 in 135 = 13% of cases) and technical failures (11 of 135 = 8%). The results of monitoring brainstem pathways contralateral to the lesion are detailed. It is concluded that the technical principles of evoked potential monitoring in posterior fossa surgery are well established. The applications and limits of this technique including its modifications are described.
Of 135 cases operated upon for posterior fossa lesions 103 showed preoperative hearing. In 34 acoustic neurinomas 14 had postoperative initially preserved hearing, in 20 microvascular decompressions 19 had preserved postoperative hearing and in 49 other lesions 5 lost hearing. The relationship between preservation of hearing and the preservation or loss of brainstem auditory evoked potentials (BAEP) waves I and V in the three groups of namely: acoustic neurinomas, microvascular decompressions and other lesions are presented. It is noteworthy that only patients with preserved waves I or V are suitable candidates for intraoperative monitoring. The loss of wave V is usually associated with hearing loss (10 out of 13 cases). But hearing loss is also possible despite preservation of wave I (3 out of 60) or despite preservation of wave V (2 out of 68). The predictive value of the preservation of waves I and V is not an absolute one, but it strongly suggests preserved hearing postoperatively. The dilemma remains that once waves I or V are lost during surgery there is no certainty as to postoperative hearing. If wave V recovers after an initial loss, hearing is usually preserved but not in all cases. In wave I amplitude changes alone were more frequent than in wave V, where latency changes alone were more frequently observed. Particular surgical manoeuvres could be found to be often associated with a wave deterioration. Hearing preservation could never be achieved in patients who already preoperatively had no BAEP. It is concluded that BAEP monitoring is of great value in surgery for microvascular decompression and cerebello-pontine-angle (CPA) tumours with preserved hearing.
Changes in vestibulospinal evoked potentials (VsEP) and motor evoked potentials (MEP) were examined in 10 cats before and after two different weight-dropping spinal cord injuries. In six animals somatosensory evoked potentials (SEP) were also monitored. The recordings were done from epidural spinal cord electrodes. Before and after severe and light weight-dropping spinal cord injuries all 3 modalities were recorded at the same time intervals till the end of 4th hour postinjury. According to a scoring system, evoked potential changes below and above the level of injury were monitored, and compared with each other. This study showed that the different motor stimulation methods use different descending spinal tracts, and both can be useful as a monitoring tool. Both descending tracts carrying VsEP and MEP had similarly remarkable changes after severe spinal cord injury. These consisted of major deformation, development of an evoked injury potential and complete potential loss. During the 4 hour monitoring period, no case showed EP recovery in the severe injury group. Light spinal cord injury caused somewhat more deterioration in MEPs than VsEP. The higher numbers of severe potential alterations in the lightly injured animals suggest that MEP is a more sensitive method for spinal cord monitoring compared to VsEP and also to SEP. On the other hand, this sensitivity might be a disadvantage during intraoperative monitoring, if MEP alone were used.
In a prospective study 144 adult patients with chronic subdural hematomas were randomly divided into three treatment groups after burr-hole evacuation. The two commonly used procedures (external closed system drainage and aspiration and irrigation without any drainage) were compared to a modified technique: permanent subdural drain with subcutaneous reservoir. After the hematoma was washed out with saline solution, a silicon catheter with multiple perforations was introduced into the subdural cavity and connected to a Rickham reservoir, fixed in the frontoparietal burr hole. In patients who showed secondary deterioration or enlargement of the residual hematoma as proven by computed tomographic scan, the reservoir was punctured and the subdural fluid aspirated. The great advantage of this method is that it is practicable at the bedside as well as in the outpatient department, thus making it possible to reduce the number of additional operations. The incidence of symptomatic residual or recurrent hematoma was similar in all three groups. The reoperation rate was 4-fold greater in the groups treated with conventional therapy, when compared to the group with the implanted system. At the same time there was no indication that the implantation of the drain was less safe, as judged by the incidence of seizures and infections.
In a retrospective study of 48 patients who underwent elective surgery for cerebral arteriovenous malformations, a statistical analysis of demographic, clinical, and neuroradiological data was undertaken in order to discover the best predictors of operative morbidity. In addition, the predictive value of different clinical grading systems as applied to this series was compared. All patients had a computed tomographic scan and a positive angiogram before surgery. Complete resection was proven angiographically. The univariate Mann-Whitney-Wilcoxon rank sum test, the Fisher exact test, Spearman's rank correlation coefficient analysis, and multivariate logistic regression were used as statistical methods. Duration of surgery, the development, of either new deficits or an increase in the preoperative neurological signs immediately after surgery, and rehabilitation (as measured by the Karnofsky index) were taken as target variables for the difficulty of operation and for postoperative morbidity, respectively. The largest diameter of the nidus of the arteriovenous malformation, eloquence of the adjacent brain, and deep venous drainage showed the most consistent correlation with these target variables. Intracerebral hematoma and other single factors, such as the age of the patient or localization of the arteriovenous malformation did not affect the outcome. The clinical grading scale of Spetzler and Martin provided better prediction of surgical risks than other proposed systems.
The general characteristics of motor evoked potentials recorded from muscle and spinal cord in response to single electrical stimulation of motor cortex were examined in 30 rats. 5 other rats were additionally examined before and after full muscle relaxation, to differentiate the volume-conducted muscle response from spinal cord responses. The first positivity (P1) recorded from the lower thoracic cord following anodal stimulation was 1.1 +/- 0.1 ms and the second positivity (P2) was 2.1 +/- 0.2 ms. P1 was present in 11 animals and P2 in 20. The later components after 2.3 ms latency recorded from the epidural spinal electrode were lost with full muscular relaxation and seem to originate from volume conducted muscular activity. A relatively stable early MEP muscle response (6.1 +/- 0.9 ms) was observed in contralateral lower extremity muscles of all animals. Following this early response, a late MEP muscle response (16.0 +/- 1.9 ms) has been recorded in 43% of all animals. This relatively inconstant and multiphasic late muscle response disappeared during vibration of same extremity tendons and has similar characteristics as Hoffmann's reflex response. Additionally, with increasing stimulus intensities, the amplitude ratio of early to late response was similar to M response/H reflex amplitude ratio. The results suggest that the late MEP muscle response is probably the result of a reflex response caused by the first/early descending volley and traveled back to the spinal cord possibly through the Ia afferents similar to that in the H-reflex.
The configuration of brainstem acoustic evoked potentials (BAEP) is influenced by the type of click stimuli used and may thus affect detectability of abnormalities. In a group of 19 patients with lesions in the posterior fossa BAEP were recorded pre- and intraoperatively. Repeat recordings were performed in each patient in two alternating series with rarefaction and condensation click stimuli. The findings demonstrated that intraoperative potential changes in latency and amplitude were different between the two stimulation modes, but did not vary significantly in their incidence. It was also not possible to predict from the preoperative BAEP which click polarity would demonstrate intraoperative changes more markedly, taking latency and amplitude as parameters. Two conclusions are drawn from this study: None of the two stimulation modes is superior in detecting intraoperative changes and therefore no recommendation can be made which click polarity to use. When working with only one click polarity it is recommended to use occasional control recordings with the other click polarity.
A series of 31 neurosurgical procedures in the posterior fossa monitored intraoperatively with ipsilateral brain stem acoustic evoked potentials (BAEPs) is analyzed for intraoperative potential changes. The evaluation of patients included pre- and postoperative BAEP recordings and pure tone audiometry. The series included 25 tumors, 4 neurovascular decompressions, 1 basilar artery aneurysm, and 1 arteriovenous malformation. Two intraoperative findings correlated significantly with a postoperative decrease in hearing: an amplitude reduction of more than 50% for Waves I to V and the loss of one of the waves, even if it was a wave that first appeared intraoperatively. We could attribute no significance to reversible or irreversible latency increases for all waves. The transient loss of one of the peaks followed by its reappearance was also insignificant with regard to postoperative hearing. A good prognostic sign was the intraoperative appearance of a peak undetectable on the preoperative recordings. These findings suggest that in intraoperative BAEP monitoring the observation of amplitude reduction is more important than that of latency increases. The surgeon should be informed when an amplitude reduction of more than 50% occurs before the peak is lost totally, as it is impossible to predict whether this peak will reappear intraoperatively.
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In 30 patients undergoing spinal disc operations, the effects of bolus injections followed by intravenous infusions of thiopental, etomidate, and midazolam on median nerve somatosensory-evoked potentials (SSEPs) were studied. Possible additive effects of fentanyl and nitrous oxide were also evaluated. Serial SSEP measurements were made before and for 25 minutes after the start of anesthesia. After induction with one of the three intravenous agents, fentanyl (10 micrograms/kg) was administered and SSEPs were again measured 1 and 5 minutes after administration. Sixty-five% nitrous oxide in 35% oxygen was administered after tracheal intubation and was followed by final SSEP measurements. The three intravenous agents affected SSEP signals differently. Etomidate increased both amplitude and latency. Thiopental decreased amplitude and increased latency. Midazolam had no effect on amplitude but increased latency. The addition of fentanyl and nitrous oxide had different effects in response to the three intravenous induction agents. This study emphasizes the differences in SSEP responses not only to different intravenous induction agents but also to the addition of fentanyl and nitrous oxide.
Based on a series of 95 neurosurgical spinal cord monitoring cases with space-occupying lesions, most of which were monitored using both spinal and cortical recordings, the use and the limits of intraoperative monitoring of sensory pathway function of the spinal cord is described. Intraoperative spinal cord monitoring performed by recording of somatosensory evoked potentials following peripheral nerve or intrathecal stimulation is shown to be a useful adjunct in cases of difficult spinal cord surgery. In our own material using both spinal and cortical recordings there have been no false-negative monitoring cases so far. In the discussion the limitations and pitfalls of this technique are reviewed.