Design of an Intensive Epilepsy Monitoring Unit

Transcription

1 Epilepsia, 41(Suppl. 5):S3-S Lippincotl Williams & Wilkins, Inc., Philadelphia 8 International League Against Epilepsy Design of an Intensive Epilepsy Monitoring Unit *Catherine A. Scott, *,?,$David R. Fish, and *Phillip J. Allen *The National Hospital for Neurology and Neurosurgery, Queen Square, London, United Kingdom;?National Society for Epilepsy, Chalfont St Peter, Buckinghamshire, United Kingdom; and $Epilepsy Research Group, Institute of Neurology, Queen Square. London, United Kingdom Summary: Video-electroencephalography (EEG) telemetry is a crucial component in the comprehensive evaluation of patients with epilepsy. The reasons for patients needing to be monitored fall broadly into three groups: presurgical assessment (36% of our patients), diagnostic assessment (52967, and sleep disorders (12%). Video EEG can be used to differentiate unusual epilepsies from pseudo seizures or other causes of paroxysmal neurological events. The design of a unit depends on the case mix of patients expected to be referred. The key elements to a successful unit are a reliable, flexible, easy-to-use recording system and a team of dedicated, experienced staff, both nursing and technical. The unit at the National Hospital is a six-bed ward with 7 nurses to provide 24-hour coverage, 5 technicians working in shifts, and physics support. A minimum of two staff are on duty at all times. It operates on a five-day week with a throughput of approximately 500 patients per year. It is vital that investigations are performed as efficiently and effectively as possible, and the patient's safety and wellbeing is paramount at all times. Drug reduction is likely to be used to precipitate seizures, especially in those being considered for epilepsy surgery, and this poses a risk of provoked secondary generalized seizures. Continuous supervision of patients, and the ability to respond rapidly to a seizure, are therefore essential. We adopt a standardized easy-to-follow drug-reduction protocol, similar to that used by other centers. Key Words: Video-EEG telemetry-epilepsy-monitoring unit. Video-electroencephalography (EEG) telemetry is a well-established and integral component in the comprehensive evaluation of patients with epilepsy. It is essential in presurgical evaluation and is often required for diagnostic purposes. It can be used to differentiate unusual epilepsies from pseudoseizures or other causes of paroxysmal neurologic events and in the investigation of sleep disorders. When the design of an epilepsy monitoring unit is considered, two key aims must be achieved: to perform the investigation in the most efficient and effective manner and to maintain the patient's safety and well-being at all times. We outline some of the issues that should be addressed in planning such a unit and in its organization and day-to-day running. Our conclusions should be seen as guidelines only. Each unit will have its own specific requirements, depending on patient case mix and the resources available. WARD LAYOUT The exact layout and the physical structure of a monitoring unit depend on the space and resource available. Address correspondence and reprint requests to Ms. Catherine Scott at Sir Jules Thorn Telemetry Unit, The National Hospital for Neurology and Neurosurgery, Queen square. London WClN 3BG. UK. However, there are some minimum requirements (1,2). A central monitoringlnursing station is essential, from which patients are kept under observation either directly or on TV monitors. On our unit this is the place at which the cameras are remotely controlled (pan, tilt, zoom, focus, and switching between monochrome and color) to ensure the best possible view of the patient at all times. A member of the staff, usually a nurse, should always be present at this central station. In the patient room, the cameras (preferably both monochrome and color) should be mounted together on a pan-and-tilt platform, facing away from the window (usually a strong source of light), and preferably above or near the television to optimize the view of the patient. We utilize color cameras during the daytime and the monochrome cameras at night, or during the day if the ambient light levels are low. The lighting in the patient room (both natural and artificial) should be adjustable, with infra-red lights installed for overnight recordings. Microphones should be positioned in the room to provide broad coverage. We use two, one at the side of the patient's bed and one by the chair. In addition to the usual nurse call button, the patient needs to have an event button to be pressed at the time of an aura or seizure. This event button should be wired so that it triggers an s3

2 s4 C. A. SCOTT ET AL. alarm at the central station and also puts a marker onto the recording system. It is preferable to locate the recording equipment in a separate room from the patient. Removing the equipment from the patient s view improves the environment, making it appear less clinical, and enables the technicians to set up the recordings, change discs and video tapes, and perform other necessary activities, away from the patient, also reducing heat and noise. If the recording equipment is in a separate room, a monitor displaying the ongoing EEG is required in the patient room. This is important to maintain recording quality, eg, when the technicians need to check the electrodes, and is necessary when the patient is being asked to perform some provocative procedure and the technician needs to monitor the ongoing EEG. On our unit, the patients are in individual rooms or bays. Because they have to spend most of their time in these rooms, it is important to consider their comfort and entertainment, We have endeavored to make the patient areas as low-tech as possible while still allowing adequate access to the patient in all parts of the room, having oxygen and suction easily available, and aiming for a safe environment should the patient become unsteady or fall. For patients entertainment, all rooms are equipped with individually controlled cable television and video recorders, and they are encouraged to bring in such things as books, personal stereos, and puzzle books to help relieve the boredom attendant on being confined to a relatively small and fixed area for several days. Other rooms that are necessary on a dedicated unit include a room for the technicians and doctors to review and report the telemetry recordings, with space for ancillary functions such as editing and archiving data. Services such as bathrooms, toilets, kitchen, and utility areas are obviously required and, if space allows, a waiting aredfamily room and a store-room are important. RECORDING EQUIPMENT As with the layout of a unit, the recording system chosen depends on individual requirements, but there are some basic standards. A monitoring unit represents a significant capital investment, and therefore long-term technical support is a key consideration in deciding which system to use, as is the reliability of the recording system in terms of minimal equipment downtime and data loss. On our unit the downtime is less than 0.1 %. The system should record the EEG data in a digital format to facilitate post-acquisition manipulation, such as re-formatting of the data into bipolar or referential montages of choice, and the ability to change the filter, gain, and timebase settings. There should be rapid access to any part of the EEG recording to facilitate effi- cient reviewing (3). Ideally, this would also apply to the video recording but, at present, economical digital video recording cannot match the quality of analogue tape recording. For patient safety, all patient-applied parts should be electrically isolated. All additional electrical equipment in the patient room is classified as medical equipment and should be specified and tested accordingly (4). For scalp recordings, 16 channels are the minimal requirement, and most systems can record up to 32 channels of physiologic parameters. A digitizing rate of 200 sarnpleds is also regarded as a minimal requirement. For intracranial studies, the ability to record up to 64 channels is normally required and a higher digitizing rate (400 samplesk) is desirable. To identify events more quickly during review and recording, automatic detection programs should be utilized. In addition to the event button (mentioned above), simultaneous spike-and-seizure detection programs are usually employed. These use established algorithms to identify seizure patterns and interictal spikes (5,6). The detections need to be validated by the reviewer but they allow a quick first-line review of the EEG data. Although they are very useful in some patients recorded on a monitoring unit (particularly those being assessed for temporal lobe surgery), they should be used with caution in patients in whom the ictal EEG may not have a rhythmic discharge, e.g., patients with extratemporal seizures or those being assessed for diagnostic reasons (e.g., patients with a parasomnia). There are differing views among those working in the field of video-telemetry as to how much of the EEG should be recorded and stored. Some centers maintain that only recording and keeping the sections of EEG identified by the seizure-and-spike detection programs (usually supplemented by periodic sampling of the wakeand-sleep background activity) is sufficient. However, this may mean that atypical and subclinical seizures are not recorded. Moreover, any subtle changes in either the EEG or electrocardiogram (ECG) that may occur before sustained ictal electrographic activity may be permanently lost. With the availability of large-capacity and relatively inexpensive digital storage media, the continuous recording of the EEG signals and subsequent archiving of the data has become a more practical and economic option. Originally, video-eeg telemetry systems recorded both the EEG and video picture on video tape and displayed it as a split-screen picture. Although this is useful for teaching purposes, allowing both the electrographic information and the clinical seizure pattern to be viewed simultaneously, this compromises both EEG and video display quality, and most commercial systems and those developed by monitoring centers no longer use this (7). Epilepsia, Vol. 41. Suppl. 5, 2000

3 EPlLEPSY MONITORING UNIT s5 RECORDING PRINCIPLES The unit at the National Hospital operates as a 5-day ward, and all patients are planned admissions with an estimated duration of stay. One advantage of a dedicated unit is the ability to manage the beds, enabling more efficient bed use. The likely length of stay is predicted in advance and is dependent on the question being asked and the frequency of the attacks. The patient is aware at the outset of the maximal length of the hospital stay and can plan accordingly. If, at the end of the patient s stay no seizures have been recorded and a repeat stay is indicated, then the patient is rebooked for a further study at the earliest possible date. In the event that patients must be monitored over the weekend (usually patients with intracranial electrodes), they are transferred to a neurosurgical ward and their EEGs are monitored by a mobile system. In planning a patient s stay on the unit, apart from predetermining the length of stay, other features of the recording may also be decided on. On arrival on the unit and with an up-to-date history from the patient, with particular reference to the current frequency of attacks and any seizure precipitants, the study can be tailored to the patient. This includes selecting the correct recording montage, adding any additional parameters where necessary (e.g., oximetry), and ensuring that any appropriate provocative procedures are carried out. All patients undergoing a presurgical assessment are routinely sleepdeprived on the second night of their stay, but if tiredness is a particular trigger sleep-deprivation is carried out more than once. Similarly, patients admitted for diagnostic assessments are sleep-derived if this is more likely to produce an attack. In planning the studies, attention should also be paid to the information that is required when the patient has an attack. For example, is it important to measure post-ictal prolactin levels? Do the blood pressure or blood sugar levels need to be recorded? It is important that all staff, nursing and technical, are aware of these points so that information is obtained promptly. The study should remain flexible and should be able to assimilate any changes that occur as the study progresses and preliminary results are obtained. Close cooperation among staff at all levels, medical, nursing, and technical, is vital. A small proportion of patients who are undergoing presurgical assessment will require intracranial studies. The indications for these invasive studies fall broadly into two categories: to further localize the epileptogenic zone within one hemisphere or to differentiate between right and left mesio-temporal lobe epilepsy. Each case has to be individually planned. The type, number, and size of the electrodes needed must be chosen, as well as their intended location. Although it is possible to start the recording as soon as the patient has recovered from the general anesthesia, in practice most centers wait until at least the following day. Patients with intracranial electrodes require extra nursing care. Apart from the postoperative care, there is maintenance of the head bandage, which is necessary to ensure that the electrodes and their connections remain secure, and an even greater degree of vigilance. Extra caution is needed with these patients because they may require a greater degree of drug reduction depending on their (post-implantation) seizure frequency, and rapid intervention may be needed to prevent them from pulling at the bandage andor electrodes during post-ictal confusion. Some of these intracranial studies also include a period of direct cortical stimulation to further localize the epileptogenic zone and to locate areas of eloquent cortex as appropriate. This procedure must be carefully planned to ensure that it is carried out in a systematic manner, and sufficient uninterrupted time must be allocated. Some centers perform the more prolonged stimulation studies on more than one day, reducing the stress and fatigue to the patient. These stimulation procedures usually involve several staff members, including the consulting neurosurgeon andor consulting neurophysiologist. STAFFING There is substantial scope for the interchange of nursing and technical staff on a monitoring unit, often dictated by the local resources and whether the unit functions as a self-contained unit or as part of a general ward. Some centers also involve family members in the seizure monitoring process, which is particularly relevant in pediatric practice. We are not aware of any comparative studies relating to effectiveness of differing skill mixes. For a dedicated unit, a minimum of two staff members must be on duty at all times. For example, our unit, which has six beds, requires seven nurses to provide 24-h coverage during the working week. The technicians also work in shifts, providing a minimum of two technicians on the ward between the hours of 8 A.M. and 8 P.M. With this regimen, the overnight technical problems are kept to a minimum and any that do arise can usually be dealt with by the nurses, sometimes with telephone advice. Although there are duties that are clearly specific to either the nursing or technical staff, working as a team is of paramount importance on a small and busy unit, and some tasks are carried out by both nurses and technicians. This is also the practice for other dedicated units (8). For example, when a seizure occurs, whoever attends to the patient first carries out the ictal testing procedure. There is also a balance between the number of EEG technicians required and junior medical staffing. Most centers employ fewer EEG technicians because junior medical staff undertake the initial review of the data and Epilepsia, Vol. 41, Suppl. 5, 2000

4 S6 C. A. SCO7T ET AL. are more involved in the day-to-day supervision of the studies. In such centers, EEG technicians primarily set up and maintain the recordings. Our higher level of technician staffing enables them to undertake first-line review of the data and to prepare factual reports on the recordings. This may be an advantage for recruitment and retention of technicians as well as continuity of the service. Given this background, each patient study typically requires 1-2 h of input from a consulting neurophysiologist who reviews and reports the data. Prolonged intracranial studies would obviously require much more direct involvement and reporting time, especially when electrical stimulation studies are performed. Minimal standards for medical personnel and technologists on a monitoring unit have been discussed previously (9). The unit staff also includes on-site physics support. One full-time physicist provides essential planned preventative maintenance, performs repairs important to minimize monitoring equipment downtime, and performs regular safety testing. The physicist also undertakes equipment and software development as needed. INDICATIONS FOR VIDEO-EEG TELEMETRY The reasons for monitoring patients fall broadly into three groups: patients who are undergoing an assessment with a view to surgery for epilepsy; those who are undergoing a diagnostic assessment; and those with sleep disorders. The relative balance of patients in these groups determines the facilities needed and recording techniques used on a monitoring unit. Because ours is a multipurpose unit, we have built a certain amount of flexibility into our recording systems to enable wider range of questions and problems to be addressed. For example, in patients who present with difficult diagnostic questions or sleep disorders, it is often necessary to record respiratory parameters (airflow, respiratory movements, oximetry, and transcutaneous CO,), and we have developed software that enables us to record and review these simultaneously with the routine EEG and ECG data. On our unit we see approximately 500 patients per year, of whom 36% are presurgical assessments, 52% are diagnostic, and 12% are for sleep disorders. Of the presurgical patients, after the initial scalp recordings, 7% undergo more prolonged studies using intracranial electrodes. The complexity of the different studies is reflected in their mean duration of stay. Sleep study patients stay 38 h, diagnostics 34 h, presurgical patients with scalp electrodes 75 h, and presurgical patients with intracranial electrodes 185 h. Using these principles and the protocols outlined below, the success rate, as determined by the number of patients in whom the question is answered, is approximately 75% (presurgical patients 82%, diagnostic 70%, and sleep 72%). Failure is usually due to inability to record attacks. In the presurgical patients, the results of the video-telemetry must be considered in the context of all the investigations carried out that provide both structural and functional data (typically MR imaging, psychometry, and a psychiatric assessment). Of the patients assessed, 40% proceed to surgery, 45% are rejected or further tests are deferred, 8% undergo further noninvasive investigations, and 7% proceed to intracranial studies, of whom two-thirds will eventually undergo surgery. PROTOCOLS Provocative procedures All patients should be asked to perform a period of hyperventilation and should be tested with intermittent flash stimulation during their period of telemetry. We routinely ask all patients whose general medical health allows to hyperventilate for a period of 5 min at least once during the recording, and this is often repeated. We perform photic testing on all patients using a standardized protocol (different flash frequencies between 2 and 50 Hz with both eyes open, closing, and closed). If a patient appears to be photosensitive, a more tailored testing procedure is invoked. As indicated earlier, the majority of presurgical assessment patients and some diagnostic patients are sleepdeprived. This is usually carried out on the second night of their stay. We ask the patients to stay awake until 2 A.M. and then they are awakened at 6 A.M. Other provocative procedures such as exercise, fasting, and eating certain foods, are carried out as is appropriate and feasible. Drug reduction Virtually all patients being assessed for epilepsy surgery require recording of habitual seizures. To facilitate seizure recording in these patients, reduction of their anticonvulsant therapy is often carried out. This has been the subject of considerable discussion in the literature, emphasizing the need to record habitual rather than atypical or withdrawal seizures and the caution that must be exercised in interpreting seizures under these circumstances (10-13). Occasionally, drug reduction is carried out in patients admitted for a diagnostic assessment, usually when repeated attempts to record a seizure have failed and to do so is crucial for diagnosis. We have set up and implemented a standardized, easyto-follow drug reduction protocol. This is discussed with the patients and their consent is sought. They are included if they have less than one partial seizure per day and less than one generalized seizure per month. In addition, patients are excluded if they have a history of status epilepticus or serial seizures with previous drug reduction, or if they are or might be pregnant at the time of the recording. If at the time of the recording the patient is experiencing a prolonged period of seizure freedom, then the studies are usually deferred. The protocol is Epilepsia, Vol. 41, Suppl. 5, 2w0

5 EPILEPSY MONITORING UNIT s7 initiated on the day of admission. On day 1 the drugs are reduced to half the normal daily dose and on day 2 (if no complex partial seizures have been recorded) the drugs are reduced to a quarter of the daily dose. This reduction protocol does not apply to anticonvulsants with an inappropriate half-life (e.g., barbiturates). If, after medication is reduced, patients experience three or more complex partial seizures in a 24-h period or a single secondary generalized seizure, they are given an immediate single dose that is equivalent to half the total daily dose of any AED that has been reduced once, and three-quarters of the total daily dose of any AED that has been reduced twice. Their normal medications may be reinstated depending on whether adequate electroclinical data have been obtained. AEDs must be reinstated at least 24 h before discharge. At this time, they are recommenced with a single additional dose as described above, depending on their regular medication and the level of drug reduction, with the regular medication taken from that time onward. This regimen is similar to that used by other centers. Swick et al. (14) have also emphasized the need to limit drug reduction to agents with appropriately short halflives and those without known potential to cause withdrawal or atypical seizures. Given these restrictions, over the past 5 years the above protocol has not been associated with an excess of severe secondarily generalized seizures, injuries, or other adverse events in the drugreduced patients compared with the non-reduced patients. This protocol works on our unit because there is continuous monitoring of the patients by nursing and technical staff, and thus a tally of seizures is kept. Should a patient experience a generalized seizure or a more prolonged complex partial seizure than is habitual, the facilities to cope are readily available (e.g., resuscitation equipment). Moreover, because there are clear guidelines for reinstatement, the nurses are able to act promptly in restoring drugs. There are, however, risks associated with drug reduction, and anyone who employs such a protocol should be aware of them and how they should be dealt with. The risks include (a) secondary generalized seizures, (b) status epilepticus, (c) atypical seizures (if there is any doubt about the seizures recorded, our practice is to show the seizure to a family member), (d) injury during seizures or post-ictally, (e) the appearance or exacerbation of postictal psychosis, and (f) there is a risk for death during a seizure. How many seizures? Knowing how many seizures or attacks to record and thus how long any particular study should last is a very patient-dependent question. The seizure history obtained from the patient or family is paramount. Regardless of whether the question is one of diagnosis or suitability for surgery, it is important to know for any patient how many different seizure types are present. Once a seizure has been recorded, is it of the patient s habitual type? If not, how does it differ? The study should continue at least until a habitual seizure has been recorded and preferably until a sufficient number are recorded to demonstrate a stereotyped electroclinical pattern. If there is more than one type of partial seizure, then the study usually continues until all types have been recorded. The concordance of all the other data is also very important, particularly for patients undergoing assessment for epilepsy surgery. With these presurgical patients, the presence of any discordant features or the risk for multiple seizure types indicates a need for recording more seizures than is necessary for patients in whom all the other anatomic and functional data are concordant and there is only a single habitual seizure type. Similarly, the absence of any structural pathology on MRI probably means that the patient will require an intracranial study, and therefore it is important to gain as much information from the scalp EEG telemetry as possible in order to plan the strategy for any invasive study. Some patients, usually but not exclusively those undergoing diagnostic assessment, can have a mixture of seizure types. For example, some patients can have a mix of epileptic and non-epileptic attacks. It has been shown in several studies that between 7 and 13% of patients with non-epileptic attacks have proven epilepsy and, if patients have any risk factors for additional epileptic seizures, then recording a single non-epileptic seizure should not lead to the conclusion that all attacks are non-epileptic. Known risk factors are an early age of onset of the seizures, the presence of interictal spikes, and a potential etiology for epilepsy (15). CONCLUSIONS The design of any monitoring unit is largely dependent on the case mix of patients expected to be referred to the unit. Are they a broad-based group needing flexible recording systems, or are they purely for presurgical assessments? If the latter, does this include patients with implanted electrodes? When patients are referred the admission must be planned to ensure that the maximal amount of information is gained while minimizing their stay in hospital. To do this, it is important to be able to review the results from any other tests before the monitoring begins and to obtain a comprehensive and current history from the patient and relatives. The two key elements to running a successful monitoring unit are a reliable recording system and a team of experienced and dedicated staff. The recording system must be flexible, robust, and easy to use, with random Epilepsin. Vol. 41, Suppl. 5, 2000

6 S8 C. A. SCOT ET AL. access of data, the means to perform post-acquisition manipulation of the data, and some means of data reduction by using automatic spike-and-seizure detection algorithms. The staff, technical and nursing, must work together to provide continuous monitoring of the patient and a prompt response when an attack occurs. The use of a set protocol for drug reduction minimizes the risks but, again, vigilance in the care of the patient in these circumstances is paramount. Above all, patient safety is a primary concern and should not be compromised by the need to record seizures while a patient is on the unit. REFERENCES Burgess RC. Space and system planning. In: Liiders H, ed. Epilepsy surgery. New York: Raven Press, 1991: lves JR. Video recording during long-term EEG monitoring of epileptic patients. In: Gunmit RJ, ed. Advances in Neurology. Vol. 46. Intensive neurodiagnostic monitoring. New York: Raven Press, Lesser RP, Webber WRS, Fisher RS. Design principles for computerized EEG monitoring. Elecrroencephalogr Clin Neurophysiol 1992;82: IEC 601-1: safety of medical electrical equipment, part I: general requiremenrs. Geneva: International Electrotechnical Commission, Gotman J, Ives JR, Gloor P. Automatic recognition of inter-ictal epileptic activity in prolonged EEG recordings. Electroencephalogr Clin Neurophysiol 1979;46: Gotman J. Automatic recognition of epileptic seizures in the EEG. Electroencephalogr Clin Neurophysiol 1982;54:53@ Vuong TA, Burgess RC. Split-screen video/eeg recording versus synchronized but separate video and EEG acquisition. In: Luders H, ed. Epilepsy surgery. New YOrk: Raven Press, 1991: Murphy D. Nursing care. In: Liiders H, ed. Epilepsy surgery. New York: Raven Press, 1991: Engel J Jr, Birchfiel J, Ebersole J, et al. Long-term monitoring for epilepsy. Report of an IFCN committee. Electroencephalogr Clin Neurophysiol 1993;87: Marciani MG, Gotman J. Effects of drug withdrawal on location of seizure onset. Epilepsia 1986:27:423-3 I. Engel J Jr, Crandall PH. Falsely localising ictal onsets with depth EEG telemetry during anticonvulsant withdrawal. Epilepsia 1983; 24: So N, Gotman J. Changes in seizure activity following anticonvulsant drug withdrawal. Neurology 1990;40: Marks DA, Katz A, Scheyer R, Spencer SS. Clinical and electrographic effects of acute anticonvulsant withdrawal in epileptic patients. Neurology 1991;41: Swick CT, Bouthillier A, Spencer s. Seizure Occurrence during long-term monitonng. Epilepsia 1996;37: Raymond A, Gilmore C, Scott c. Fish D, Smith S. Video-EEG telemetry: apparent manifestation of both epileptic and nonepileptic attacks causing potential diagnostic pitfalls. Epileptic Disord 1999; 1: Epilepsio, Vol. 41, Suppl. 5, 2000