S. Fossi

Continuous EEG-SEP monitoring of severely brain injured patients in NICU: methods and feasibility.

AIMS To evaluate the feasibility of a continuous neurophysiologic monitoring (electroencephalography (EEG)-somatosensory evoked potentials (SEPs)) in the neuro-intensive care unit (NICU), taking into account both the technical and medical aspects that are specific of this environment. METHODS We used an extension of the recording software that is routinely used in our unit of clinical neurophysiology. It performs cycles of alternate EEG and SEP recordings. Raw traces and trends are simultaneously displayed. Patient head and stimulator box are placed behind the bed and linked to the ICU monitoring terminal through optic fibers. The NICU staff has been trained to note directly clinical events, main artefacts and therapeutic changes. The hospital local area network (LAN) enables remote monitoring survey. RESULTS Continuous EEG (CEEG)-SEP monitoring was performed in 44 patients. Problems of needle detachment were seldomly encountered, thanks to the use of a sterile plastic dressing, which covers needles. We never had infection or skin lesions due to needles or the electrical stimulator. The frequent administration of sedative at high doses prevented us from having a clinically valuable EEG in several cases but SEPs were always monitorable, independently of the level of EEG suppression. The diagnosis of seizures and non-epileptic status was based on raw EEG, while quantitative EEG (QEEG) was used to quantify ictal activity as a guide to treatment. CONCLUSIONS EEG and EP waveforms collected in NICU were of comparable quality to routine clinical measurements and contained the same clinical information. A continuous SEP monitoring in a comatose and sedated patient in NICU is not technically more difficult and potentially less useful than in operating room. This monitoring appears to be feasible provided the observance of some requirement regarding setting, electrodes, montages, personnel integration, consulting and software.

Evoked potentials in the ICU

Summary The most informative neurophysiological techniques available in the neurosurgical intensive care unit are electroencephalograph and somatosensory evoked potentials. Such tools, which give an evaluation of cerebral function in comatose patients, support clinical evaluation and are complementary to neuroimaging. They serve both diagnostic/prognostic and monitoring purposes. While for the former, discontinuous monitoring is sufficient, for the latter, to obtain increased clinical impact, continuous monitoring is necessary. To perform and interpret these examinations in the neurosurgical intensive care unit, both the technician and the neurophysiologist need specific training in the intensive care field. There is sufficient evidence to show that somatosensory evoked potentials are the best single indicator of early prognosis in traumatic and hypoxic‐ischaemic coma compared to the Glasgow Coma Score, computed tomography scan and electroencephalograph. Indeed, somatosensory evoked potentials should always be combined with clinical examination to determine the prognosis of coma. Despite widespread use of somatosensory evoked potentials and their prognostic utility in acute brain injury, few studies exist on continuous somatosensory evoked potential monitoring in the intensive care unit. We carried out a pilot study of continuous electroencephalograph‐somatosensory evoked potential monitoring in the neurosurgical intensive care unit (traumatic brain injury and intracranial haemorrhage, Glasgow Coma Score <9, intracranial pressure monitoring). All patients stable from a clinical and computed tomography scan point of view showed no significant somatosensory evoked potential modifications, while in the case of clinical deterioration (23%), somatosensory evoked potentials always showed significant modifications. While somatosensory evoked potentials correlated with short‐term outcome, intracranial pressure showed a poor correlation. We believe neurophysiological monitoring is an ideal complement to the other parameters monitored in the neurosurgical intensive care unit. Whereas intracranial pressure is simply a pressure index, electroencephalograph‐somatosensory evoked potential monitoring reflects to what extent cerebral parenchyma still remains metabolically active during acute brain injury.

Anoxic-ischemic alpha coma: prognostic significance of the incomplete variant

Abstract.The prognostic significance of post-anoxic-ischemic alpha coma (AC) is controversial. We recorded somatosensory evoked potentials (SEPs) and performed serial electroencephalography (EEG) in a 60-year-old woman in coma after cardiac arrest. The first EEG was recorded after 48 hours (GCS=5; E1-V1-M3); brain-stem reflexes were preserved. The EEG pattern showed monotonous alpha frequencies (10–11 Hz) with posterior predominance; acoustic and noxious stimuli evoked EEG reactivity. Early cortical SEPs (72 h) were normal. On the fifth day (GCS=8; E4-V1-M3), the EEG alpha pattern was replaced by a diffuse delta activity; rhythmic theta changes appeared spontaneously or in response to stimuli. The patient regained consciousness on the tenth day and EEG showed posterior theta activity (6–7 c/s) partially reactive to stimuli. At the 6-month follow-up, cognitive evaluation showed mild dementia. Recent studies identified two forms of AC. Patients with complete AC have an outcome that is almost invariably poor. Conversely, incomplete AC (posteriorly accentuated alpha frequency, reactive and with SEPs mostly normal) reflects a less severe degree of anoxic-ischemic encephalopathy. The case we report should be classified, according to the SEPs and EEG features, as incomplete AC. The fact that the patient has regained consciousness, even if with residual cognitive impairment, confirms the need to distinguish this variant from complete AC.

Proposal of a new criterion for electrodiagnosis of meralgia paresthetica by evoked potentials

We examined 19 subjects with meralgia paresthetica (bilateral in three cases), recording bilateral somatosensory-evoked potentials (SSEPs) after stimulation of the tibial posterior nerve (TPN) and cutaneous stimulation in the region of the lateral femoral cutaneous nerve (LFCN). We calculated the difference between TPN SSEPs and LFCN SSEPs cortical potentials, identifying a temporal parameter that we termed DSEP. We defined DSEP normal values in a control group. DSEP evaluation showed good sensitivity and specificity (85.7% and 82.4%, respectively; accuracy, 83.3%) in discriminating affected limbs from unaffected. The main advantage of this method is to disengage from the necessity of contralateral comparison of LFCN recordings, joined with a reduction of interindividual variability of LFCN SSEPs amplitude and latency that often causes a lower sensitivity of other methods. As an interesting consideration, DSEP evaluation appears to mark out a possible subclinical involvement of LFCN in the asymptomatic side of patients with meralgia paresthetica.

P11.8 Direct muscle stimulation versus composed motor action potential (CMAP) duration for the diagnosis of critical illness “neuromyopathy”: evaluation of sensitivity and specificity

implantation procedure is performed under local anaesthesia with intraoperative neurophysiological monitoring (microelectrode recording and micro or macrostimulation) for the optimal targeting and for the evaluation of stimulation-induced clinical or adverse effects. Objectives: To evaluate the feasibility of microelectrode recording for deep brain stimulation surgery in parkinsonian patients under general anaesthesia using a specific ketamine-based anaesthetic protocol and to compare the neurophysiological data obtained under these conditions with those ones obtained in the same patients previously underwent to surgery under local anaesthesia. Methods: 5 patients affected by advanced Parkinson’s disease underwent to bilateral subthalamic nucleus stimulation at first under local anaesthesia and then, owing some surgical device complications, under general anaesthesia with a total intravenous protocol based on remifentanyl and ketamine infusion. Neurophysiological data obtained under local and general anaesthesia were then analysed and compared with an off-line spike sorting software (FSPS-University of Ferrara) and a statistical analysis. Results: For all the neurophysiological parameters analysed, we didn’t find any statistical significative difference between the first and second surgical procedure. Conclusions: Subthalamic nucleus stimulation for advanced Parkinson’s disease with microelectrode recording guidance is possible and reliable under a ketamine-based general anaesthesia. So, even if awake surgery represents the “gold standard” for functional neurosurgery, general anaesthesia can be an alternative for those patients who don’t accept awake surgery because of clinical reasons, such as massive fear, reduced cooperativity, or severe “off”-medication effects.

P11.15 Continuous EEG-SEP monitoring of acute brain injury in neurointensive care unit

P11.15 Continuous EEG-SEP monitoring of acute brain injury in neurointensive care unit S. Fossi1, R. Carrai1, A. Amadori2, L. Bucciardini2, P. Innocenti2, C. Cossu1, S. Gabbanini1, S. Lori1, F. Pinto1, A. Grippo1, A. Amantini1 1SOD Neurofisiopatologia, DAI Neuroscienze, Azienda Ospedaliera Universitaria Careggi, Florence, Italy, 2SOD Anestesia e TI Neurochirurgica, DAI Neuroscienze, Azienda Ospedaliera Universitaria Careggi, Florence, Italy

P12.1 Nonconvulsive status epilepticus in acute brain injury: a prospective continuous EEG study

P11.15 Continuous EEG-SEP monitoring of acute brain injury in neurointensive care unit S. Fossi1, R. Carrai1, A. Amadori2, L. Bucciardini2, P. Innocenti2, C. Cossu1, S. Gabbanini1, S. Lori1, F. Pinto1, A. Grippo1, A. Amantini1 1SOD Neurofisiopatologia, DAI Neuroscienze, Azienda Ospedaliera Universitaria Careggi, Florence, Italy, 2SOD Anestesia e TI Neurochirurgica, DAI Neuroscienze, Azienda Ospedaliera Universitaria Careggi, Florence, Italy

P11.5 Hypoxic ischemic coma: somatosensory evoked potentials recorded during hypothermia retain their prognostic value

Introduction: During cerebral aneurysms surgery, could appear isquemic complications because of an artery occlusion. The changes depend of the cerebrovascular auto regulation, collateral perfusion and systemic homeostasis parameters. Objective: Assess intraoperative neurophysiologic monitoring outcomes of patients whom were operated or cerebral aneurysms. Methods: We present a total of 17 patients with intracranial aneurysms, that was intraoperative monitored with somatosensory evoked potentials (SEP) and motor evoked potentials (MEP). Results: Isquemic time during temporal clip collocation was 4 minutes in 11 cases, and in 6 cases between 1 second and 25 minutes. In 3 patients there was a change in SEP and MEP during the clipping. Patient 1: absence of SEP after 30 seconds aneurysm clipping without posterior recover and postoperative left hemiplegic. MEP with no changes. Patient 2: 50% amplitude reduction of SEP and MEP, when the aneurysm clipping with posterior recover and not postquirugic neurological sequel. Patient 3: 50% amplitude reduction of SEP after 6.86 minutes aneurysm clipping and a second amplitude SEP reduction alter 1.10 minutes, both of them with posterior recover and not postoperative neurological sequel. No changes in MEP. Conclusions: In our knowledge, the most sensitive parameter to detect isquemia was the SEP. MEP is not reliable, probably because it can bypass isquemic site by distal stimulation. The clipping duration was not related with the changes on SEP and MEP, maybe because of the presence of collateral arteries. Nevertheless it would be required more number of cases to determine the time of clipping and sensitive parameters to define isquemic complications.

FC29.3 Monitoring of acute brain injury in neurointensive care unit : Neurophysiological and ICP correlation with outcome

unit : Neurophysiological and ICP correlation with outcome S. Fossi , A. Amantini , A. Grippo , C. Cossu , P. Innocenti , L. Bucciardini , F. Pinto 1 1 Unit of Clinical Neurophysiology, Department of Neurological and Psychiatric Sciences Azienda Ospedaliero Universitaria Careggi, Italy 2 Neurosurgical Intensive Care Unit, Department of Neurological and Psychiatric Sciences Azienda Ospedaliero Universitaria Careggi, Italy

P33.2 Neurological deterioration until brain death: Neurophysiological, clinical and TCD findings

Background: Variability of muscle-fiber conduction velocity (MFCV) is a main source of myogenic jitter in voluntarily activated muscle. MFCV is known to depend on a fiber’s firing history. This dependence is summarized by the velocity recovery function (VRF), which describes the relationship between MFCV and the fiber’s previous inter-discharge interval (IDI). MFCV variability and the VRF have usually been studied using electrical stimulation rather than voluntary activation. Aim: To examine how well the VRF explains MFCV variability during voluntary contractions. Methods: EMG signals were recorded simultaneously from four locations along the proximodistal axis of the brachioradialis muscle during 20-s voluntary contractions in 6 healthy subjects. The signals were decomposed into trains of motor-unit (MU) discharges. MFCV was calculated from inter-potential intervals measured between MU components in the same or different channels. Results: A total of 87 MUs were studied. The following aspects of MFCV variability were found to be not fully explained by the VRF: (1) MFCV increased by 8.9 ± 2.5% during the first 15 to 35 discharges after recruitment, settling exponentially towards a steadystate value. (2) The steady-state value decreased continuously throughout the contraction at a rate of up to 0.02%/s. (3) MFCV fluctuations followed the smoothed firing rate more closely than the instantaneous firing rate. (4) After intermittent decreases in contractile effort, MFCV took much longer to recover than firing rate. Conclusion: When a MU is first recruited and after a long IDI it takes some time for the MFCV to reach a steady-state value. During this period the MFCV does not follow exactly the predictions of the VRF. In voluntary contractions, corrections for MFCV variability should take more than just one preceding IDI into account. In order to avoid excessive myogenic jitter, jitter measurements should not begin until several seconds after recruitment.