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At least 1,099 records · Page 61Linked to original sources
PubMed2004

Ellen R. Grass Lecture: Motor evoked potential monitoring.

Because somatosensory evoked potentials (SSEPs) recorded from the brain are carried solely within the dorsal columns of the spinal cord, SSEP monitoring may fail to detect damage to the spinal cord motor pathways, and techniques for directly monitoring the motor pathways have been developed. Transcranial magnetic brain stimulation is useful for extraoperative evaluation of the motor system, but anesthetic effects on cortical synaptic activity limit its usefulness for intraoperative monitoring. Another proposed monitoring technique, rostral spinal cord stimulation with recording from peripheral nerves, predominantly reflects retrograde conduction within the dorsal columns; like SSEPs, this technique may fail to detect motor pathway damage. The true motor evoked potential (MEP) monitoring technique preferred by most institutions involves transcranial electrical brain stimulation. This stimulates the corticospinal tract axons directly, producing a D-wave in them. There may be additional corticospinal tract volleys, reflecting indirect activation of the pyramidal cells via synapses from cortical interneurons; these I-waves are largely suppressed by anesthesia. Temporal summation at the alpha motor neuron synapse is necessary to elicit myogenic MEPs (M-waves) under anesthesia; this is accomplished with brief trains of stimuli that produce multiple pyramidal tract volleys. High stimulus intensities are required to stimulate the brain through an intact skull; with proper precautions, this is acceptably safe. Myogenic MEPs are quite sensitive to anesthesia and show considerable run-to-run variability. Therefore, criteria for evaluating MEPs differ from those for SSEPs, and the anesthetic regimen and degree of neuromuscular blockade must be carefully controlled. SSEPs should be monitored concurrently with MEPs, because the dorsal columns may be affected without compromise of the motor tracts, and also because this provides redundancy, with two independent assessments of spinal cord function.

Brain↗
PubMed1990

Intraoperative use of ultrasound in arterial surgery.

Technical perfection is the goal of any arterial reconstruction so as to avoid postoperative complications. Experimental and clinical studies have clearly shown that these operations are imperfect and that some form of intraoperative surveillance is required to decrease the incidence of correctable technical defects. Ultrasound technology is uniquely suited for this role. This article describes the distinct advantages of duplex ultrasound for the intraoperative monitoring of vascular reconstructions.

Arterial Occlusive Diseases↗
PubMed1996

Fatal pulmonary embolization after reaming of the femoral medullary cavity in sclerosing osteomyelitis: a case report.

Reaming of the medullary may be used in cases of sclerosing osteomyelitis (type Garré), refractory to other methods. We report a case of fatal intraoperative complication related to this procedure. An otherwise healthy young patient died during reaming using a machine-driven reamer of the femoral medullary canal due to pulmonary bone embolism. The technique and the indication for this procedure as well as the intraoperative monitoring options are discussed.

Adult↗
PubMed1988

[Neurophysiological monitoring (electroencephalogram, evoked potentials) and the effects of benzodiazepines].

Since the introduction of diazepam, flunitrazepam and midazolam into clinical practice benzodiazepines have been increasingly used for premedication, induction of anesthesia, and long-term sedation in the intensive care unit utilizing their anxiolytic and sedative components. Intraoperative monitoring of central nervous structures has to take into account the effects of benzodiazepines on the electroencephalogram (EEG) and evoked potentials (EP) before their contribution to alterations in brain electrical activity during balanced anesthesia with combination of different drugs can be evaluated. EEG reflects the spontaneous brain electrical activity whereas EP are the averaged time-locked electrical responses to external stimulation. They are thus able to assess the functional integrity of afferent neuronal pathways from peripheral nerves to cortical areas. The specific benzodiazepine antagonist flumazenil binds competitively to benzodiazepine receptors and is able to induce a change in pharmacodynamic parameters, which i.e. can be measured by EEG- and EP-recordings. Characteristical changes in the EEG after benzodiazepine medication consist in an activation of higher EEG-frequencies simultaneous to a decrease in alpha-activity. A facultative increase in delta-activity seems to be dependent on the absolute dose administered and on the speed for intravenous injection. Benzodiazepine-induced EEG-alterations can be reversed by flumazenil almost completely but in the time course will change again in correspondence to the plasma levels of the benzodiazepines and the half-time of flumazenil. Cortical EP-components are suppressed by benzodiazepines whereas subcortical generated potentials are not altered.(ABSTRACT TRUNCATED AT 250 WORDS)

Anesthesia↗
PubMedDate not supplied

[Update on cerebral monitoring and protective methods].

Clamping ischaemia is responsible for the 20-30% of the neurological complications during carotid surgery. It is impossible at present to determine preoperatively for certainty the patients who are at risk and the ones who are not at risk for clamping ischemia. Intraoperative monitoring is mandatory in all the cases to point out cerebral ischemia and to prevent neurological deficit with an adequate brain protection. Methods used to predict brain ischaemia include local anesthesia, EEG, SEP, stump pressure measurement, transcranial doppler, regional cerebral blood flow measurement and evaluation of venous blood gases from the internal jugular vein. Local anesthesia is a safe and simple method of assessing cerebral ischemia during carotid clamping but has some limits particularly in case of brain ischaemia for the technical difficulties to install an indwelling shunt in an awake and often troubled patient. Moreover the only possibility of cerebral protection under local anesthesia is an increase in systemic blood pressure with a resulting growth in cardiac morbidity and mortality. For these reasons operation should be performed under general anesthesia to assure a better farmacogical brain protection when preoperative evaluation demonstrates a reduction of cerebral vasoreactivity, with a consequent high risk of clamping ischemia. At present EEG is one of the most used technique of cerebral monitoring under general anesthesia with a sensibility and specificity in the diagnosis of brain ischaemia that is about 90%. The best cerebral protection is obtained with a selective shunting. Burst suppression, with high dose thiopentone, has recently demonstrated its reliability alone or in association with an indwelling shunt in patients at high risk for clamping ischaemia. Of course a systematic cerebral protection together with an accurate control of the blood pressure is necessary in all the patients. This behaviour allowed us to obtain good results in the last 500 patients with a morbidity and mortality respectively of 1% and 1.6% with no significant differences between patients who tolerated carotid clamping and those with clamping ischaemia.

Blood Pressure Determination↗
PubMed1994

Vagal Nerve Monitoring during Parapharyngeal Space Tumor Removal.

The vagus nerve innervates the intrinsic and extrinsic laryngeal musculature as well as the complex pharyngeal plexus. Acute paralysis of this nerve results in dysfunctional speech, deglutition, and airway protection. These untoward effects, which lead to additional infectious and aerodigestive complications, may arise following manipulation of the vagus nerve during the surgical removal of a variety of neoplasms found in the parapharyngeal space.The vagal nerve has been intraoperatively monitored in an effort to maintain its anatomic and functional integrity. Bipolar hook-wire electrodes are introduced transcutaneously through the cricothyroid membrane and are guided into the vocalis muscle by an assistant performing direct laryngoscopy. Continuous, real-time monitoring of the vagal nerve is provided by audio and visual feedback to the operating surgeon. Potentially injurious stretching, heating, and compression of the nerve are easily detected, and monopolar stimulation of the nerve is used to map the nerve's course through the tumor bed.This presentation outlines our technique for vagal nerve monitoring in patients with tumors of the parapharyngeal space and intact preoperative vocal cord mobility. Selected cases are presented and illustrated through intraoperative and postoperative videotapes.

Journal Article↗
PubMedDate not supplied

[Detection of microembolus with transcranial doppler].

OBJECTIVES: To review techniques and the most important clinical applications of microembolus detection with transcranial Doppler. DEVELOPMENT: Technical aspects of microembolus detection are discussed initially; clinical circumstances in which embolus detection is currently used follow, such as carotid stenosis, cardiac pathology, monitoring during neuroangiography, coronary revascularization surgery and endarterectomy. Lastly, the potential clinical applications of this technique are reviewed: localization of an embolic source, risk of recurrent ischemia in patients with unstable atherosclerotic plaques, intraoperative monitoring and potential surgical technique modifications based on this information, contributions to the understanding of the pathophysiology of the fat embolism syndrome, and monitoring therapeutic efficacy of antithrombotics and thrombolytics. CONCLUSIONS: The ability to detect cerebral emboli with transcranial ultrasound has increased significantly our understanding about the pathogenesis of cerebral ischemia. Microembolus detection with transcranial Doppler is a powerful and novel diagnostic technique that allows to study the embolic process in vivo and in real time, instead of using indirect indicators of embolism (clinical and radiological features, possible embolic sources, etc.).

Brain Ischemia↗
PubMed2000

Combining the selective arterial calcium injection test and intraoperative blood glucose monitoring for multiple insulinomas: report of two cases.

To date, no precise methods of preoperatively localizing multiple insulinomas or intraoperatively confirming their complete removal have been established. We describe herein the effectiveness of combining the selective arterial calcium injection (SACI) test to locate tumors preoperatively, with intraoperative continuous blood glucose monitoring (IOBGM) to confirm their complete removal. During the 8-year period from 1990 to 1997, we experienced two patients with multiple insulinomas. The first patient required resection of a residual tumor in the remnant pancreas for persistent hyperinsulinemia after a distal pancreatectomy performed under conventional diagnostic procedures. In the second patient, a SACI test was performed in addition to other diagnostic imaging procedures, and while computed tomography scan, endoscopic ultrasonography, and arteriography demonstrated multiple tumors in the body and tail of pancreas, the SACI test suggested that there were also tumors in the head of pancreas. Intraoperative ultrasonography showed a tumor measuring 5 mm in diameter on the surface of the head of the pancreas, apart from the multiple tumors in the body and tail of the pancreas. Complete removal of all tumors was assessed by the hyperglycemic rebound after resection of the tumors, determined by IOBGM. Based upon our experience, we believe that the SACI test and IOBGM are helpful for establishing precise localization and achieving complete removal of multiple insulinomas.

Blood Glucose↗
PubMedDate not supplied

Interstitial pH value in the myocardium as indicator of ischemic stress of cardioplegically arrested hearts.

The influence of different cardioplegic methods (Bretschneider, Cardiac Surgery in Hamburg, Kirklin, St. Thomas' Hospital in London) on the progressive myocardial acidosis during global ischemia of up to 24 hours' duration was investigated in arrested, nonperfused canine hearts (n = 36). The increasing acidosis of the ischemic heart muscle was continuously measured and registered with the aid of interstitial pH measurement (pHi) using glass implant electrodes. With various buffered and unbuffered cardioplegic solutions there were relatively wide fluctuations of the pHi courses in the myocardial extracellular space. The "critical" interstitial pH values ("pHcrit") relative to a defined myocardial ATP concentration (4 mumol/g ww) vary between 6.10 (Bretschneider) and 5.6 (Kirklin) (p less than 0.001). These striking results cannot be attributed solely to different total myocardial lactate concentrations, but variations in a "cellular" and an "extracellular factor" must also be taken into account. Measurement of interstitial pH for intraoperative monitoring of myocardial ischemic stress can therefore be used only within limits and with knowledge of the specific protective procedure applied. The method continues an important tool in basic investigations of partial or global ischemia of organs, particularly as regards the spectrum of metabolic, morphological and functional parameters.

Acidosis↗
PubMed1987

Evolving concepts in prevention of spinal cord injury during operations on the descending thoracic and thoracoabdominal aorta.

Spinal cord injury following operations on the descending thoracic or thoracoabdominal aorta remains a major problem. In certain subsets of patients, the risk of postoperative spinal cord injury is substantial. Although several adjuncts have been employed clinically to eliminate or reduce the frequency of this complication, none have proven to be completely effective. An important reason for this is the failure of these techniques to reliably and noninvasively localize the level of origin of arteries from the aorta that are critical to spinal cord circulation. Since postoperative spinal cord injury most likely results from ischemia or hypoxia of the lower segment of spinal cord, use of adjunctive techniques to preserve spinal cord function during aortic clamping by perfusing the distal aorta adequately with or without systemic hypothermia should be considered. To practically implement this, partial cardiopulmonary bypass for distal perfusion when the critical intercostal or lumbar arteries originate from the aorta distal to the excluded segment, and total cardiopulmonary bypass with systemic hypothermia and implantation of intercostal and lumbar arteries when these arteries originate from the excluded segment, can be used. In addition, whenever possible, intraoperative monitoring of spinal cord function should be performed.

Animals↗
PubMed1988

Phase space electroencephalography (EEG): a new mode of intraoperative EEG analysis.

Intraoperative monitoring of electroencephalography (EEG) data can help assess brain integrity and/or depth of anesthesia. We demonstrate a computer generated technique which provides a visually robust display of EEG data plotted as 'phase space trajectories' and a mathematically derived parameter ('dimensionality') which may correlate with depth of anesthesia. Application of nonlinear mathematical analysis, used to describe complex dynamical systems, can characterize 'phase space' EEG patterns by identifying attractors (geometrical patterns in phase space corresponding to specific ordered EEG data subjects) and by quantifying the degree of order and chaos (calculation of dimensionality). Dimensionality calculations describe the degree of complexity in a signal and may generate a clinically useful univariate EEG descriptor of anesthetic depth. In this paper we describe and demonstrate phase space trajectories generated for sine waves, mixtures of sine waves, and white noise (random chaotic events). We also present EEG phase space trajectories and dimensionality calculations from a patient undergoing surgery and general anesthesia in 3 recognizable states: awake, anesthetized, and burst suppression. Phase space trajectories of the three states are visually distinguishable, and dimensionality calculations indicate that EEG progresses from 'chaos' (awake) to progressively more 'ordered' attractors (anesthetized and burst suppression).

Electroencephalography↗
PubMed1987

Monitoring of somatosensory evoked potentials during surgical procedures on the thoracoabdominal aorta. IV. Clinical observations and results.

Thirty-three patients undergoing operations on the descending thoracic or thoracoabdominal aorta were monitored to evaluate causes and effects of spinal cord ischemia as manifested by changes in somatosensory evoked potentials. Maintenance of distal aortic perfusion pressure (greater than 60 mm Hg) by either shunt or bypass techniques in 17 patients resulted in preservation of somatosensory evoked potentials and a normal postoperative neurologic status, irrespective of the interval of thoracic cross-clamping (range 23 to 105 minutes). In 16 other patients in whom cross-clamp time ranged from 16 to 124 minutes, evoked potential loss was observed because of failure to provide distal perfusion (n = 8), inadequate maintenance of distal perfusion pressure (less than 60 mm Hg) despite shunt/bypass (n = 6), or interruption of critical intercostal arteries (n = 2). Incidence of paraplegia in the entire group was 15.1% (5/33) and was limited to only those patients in whom evoked potential loss occurred (5/16, 31.2%) (p = 0.02). Loss of somatosensory evoked potentials for more than 30 minutes resulted in a 71.2% (5/7) incidence of paraplegia, whereas no neurologic deficit was noted in patients (0/26) in whom evoked potential loss was either prevented or limited in duration to 30 minutes (p less than 0.001 versus loss for more than 30 minutes). Intraoperative monitoring of somatosensory evoked potentials is a sensitive indicator of spinal cord ischemia. Simple aortic cross-clamping, failure to maintain distal perfusion pressure above 60 mm Hg, and inability to reimplant critical intercostals in a timely fashion result in a high rate of paraplegia if duration of spinal cord ischemia as measured by somatosensory evoked potentials exceeds 30 minutes. Routine evoked potential monitoring during thoracoabdominal procedures appears useful in assessing the adequacy of spinal cord perfusion. Furthermore, it can alert the surgeon to the necessity for critical intercostal artery reimplantation as well as the need for adjustment or regulation of distal aortic perfusion.

Adolescent↗
PubMed1986

Pathophysiological mechanisms of intraoperative and postoperative hearing deficits in cerebellopontine angle surgery: an experimental study.

Pathophysiological mechanisms responsible for intraoperative and postoperative hearing deficits associated with cerebellopontine (CP) angle operations were explored experimentally in dogs. The CP angle operative manipulations performed were the same as those experienced by human patients, and auditory evoked potentials were monitored intraoperatively. As a result of the operative manipulations, petechial or confluent hemorrhages occurred at the compressed portions of the cochlear nerve, and intravascular clots were often observed. Disintegration of the nerve fibers was verified by ultrastructural examination. Moreover, rupture of the microvasculature within the cochlear nerve occurred at locations remote from the operative site, due to stretching of the nerve trunk. The Obersteiner-Redlich zone, the Schwann-glial junction of the cochlear nerve, was a locus minoris resistentiae in CP angle surgery; the vasa nervorum easily bled at this zone and the peripheral and central myelins easily separated at their junctional zones ("central" avulsion injury). Intracochlear hemorrhages were identified as the most probable cause of the sudden loss of all components of the auditory evoked potentials, a frequent predictor of postoperative hearing loss, although rupture, occlusion, or vasospasm of the main trunk of the internal auditory artery have also been implicated as possible causes of such hearing losses. The results of this study show that hearing preservation is highly dependent on preserving not only the nerve at the operative site but also the remote O-R zone and intracochlear structures.

Animals↗
PubMed2004

Comparison of monitoring techniques for intraoperative cerebral ischemia.

OBJECTIVE: To prospectively compare somatosensory evoked potentials, electroencephalography (EEG) and transcranial Doppler ultrasound (TCD) for detection of cerebral ischemia during carotid endarterectomy (CEA). METHODS: Somatosensory evoked potentials and EEG recordings were attempted in 156 consecutive CEAs and TCD was also attempted in 91 of them. Recordings from all three modalities were obtained for at least 10 minutes before CEA, during CEA and for at least 15 minutes after CEA. Somatosensory evoked potentials peak-to-peak amplitude decrease of >50%, EEG amplitude decrease of >75%, and ipsilateral middle cerebral artery mean blood flow velocity (mean VMCAi) decrease >75% persisting for the entire period of internal carotid artery occlusion were individually considered to be diagnostic of cerebral ischemia. Clinical neurological examination was performed immediately prior to surgery and following recovery from general anaesthesia. RESULTS: Somatosensory evoked potentials, EEG, and TCD were successfully obtained throughout the entire period of internal carotid artery occlusion in 99%, 95%, and 63% of patients respectively. Two patients (1.3%) suffered intraoperative cerebral infarction detected by clinical neurological examination and subsequent magnetic resonance imaging. Somatosensory evoked potentials accurately predicted intraoperative cerebral infarction in both instances without false negatives or false positives, EEG yielded one false negative result and no false positive results and VMCAi one true positive, four false positive and no false negative results. Transcranial Doppler ultrasound detection of emboli did not correlate with postoperative neurological deficits. Nevertheless the sensitivity and specificity of each test was not significantly different than the others because of the small number of disagreements between tests. CONCLUSION: A >50% decrease in the cortically generated P25 amplitude of the median somatosensory evoked potentials, which persisted during the entire period of internal carotid artery occlusion, appears to be the most reliable method of monitoring for intraoperative ischemia in our hands because it accurately detected both intraoperative strokes with no false positive or false negative results.

Aged↗
PubMed2005

Venous air embolism during deep brain stimulation surgery in an awake supine patient.

Deep brain stimulation (DBS) of the subthalamic nucleus and globus pallidus is used to improve Parkinsonian symptoms and reduce levodopa-induced motor complications in Parkinson's disease (PD). This procedure is usually performed with minimal or no sedation to allow accurate feedback from patients during surgery. Venous air embolism (VAE) has been previously reported in patients undergoing awake neurosurgical procedures for brain tumors or pallidotomy for PD. We describe a case of intraoperative VAE in an awake, supine patient while undergoing DBS surgery for PD who presented with coughing, tachypnea and hypoxemia. The difference in clinical presentation between VAE in awake vs. anesthetized patients is discussed as are intraoperative monitoring techniques and management options.

Cerebral Veins↗
PubMed1989

The use of electroencephalography and brain protection during operation for basilar aneurysms.

Intraoperative monitoring with electroencephalography and the use of brain protection with steroids, phenytoin, mannitol, and pentobarbital or etomidate were evaluated in 15 patients undergoing operation for an aneurysm of the upper basilar artery. One patient harbored a basilar trunk aneurysm, 1 an aneurysm of the proximal posterior cerebral artery, 3 an aneurysm of the superior cerebellar artery, and 10 an aneurysm at the basilar tip. The size of the aneurysms varied between 5 and 30 mm. Subarachnoid hemorrhage was the symptom exhibited in 12, mass effect the symptom in 2, and 1 patient was asymptomatic but had an angiogram because of amaurosis. There were 9 patients with multiple aneurysms, 5 of whom had aneurysms of the bilateral anterior circulation. Four patients underwent operation early. In 2 patients, the basilar artery was the sole or main blood supply of the whole brain. All patients except the one with the basilar trunk aneurysm were operated on via a transsylvian approach. All patients received 500 to 800 mg of phenytoin and 10 to 20 mg of dexamethasone shortly before and during surgery, and mannitol (0.8 g/kg) 15 minutes before the induction of hypotension or temporary clipping. Three patients showed slowing of electrical activity over the right hemisphere as a result of retraction of the internal carotid artery; with repositioning of the retractor, this disappeared within 10 minutes. Electrocortical silence was induced in 8 patients; this was in anticipation of prolonged moderate hypotension in 2, short deep hypotension in 2, temporary clipping of major vessels--including the basilar artery--in 2, and a combination of deep hypotension combined with temporary clipping in 2.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1991

The impact of continuous electrophysiological monitoring on preservation of the facial nerve during acoustic tumour surgery.

Continuous electromyographic (EMG) activity and responses to electrical stimulation of the facial nerve were monitored intraoperatively in 35 patients undergoing primary removal of acoustic neuroma. The rate of anatomical and immediate functional preservation of the facial nerve of these patients was compared with a matched population where a facial nerve stimulator and monitoring of facial muscle contraction by the anaesthetist only was employed. Overall, 94% (n = 33) of facial nerves were preserved anatomically in patients with continuous EMG monitoring, compared with 64% (n = 89) of patients (n = 139) without continuous monitoring. Amongst the 33 cases with anatomical facial nerve preservation, 64% (n = 21) had immediate functional preservation. Immediate functional preservation was only achieved in 39% (n = 35) of anatomically preserved facial nerves (n = 89) where conventional monitoring was used.

Electromyography↗