Brainstem Monitoring in the Neurocritical Care Unit: A Rationale for Real-Time, Automated Neurophysiological Monitoring.

Patients with severe traumatic brain injury or large intracranial space-occupying lesions (spontaneous cerebral hemorrhage, infarction, or tumor) commonly present to the neurocritical care unit with an altered mental status. Many experience progressive stupor and coma from mass effects and transtentorial brain herniation compromising the ascending arousal (reticular activating) system. Yet, little progress has been made in the practicality of bedside, noninvasive, real-time, automated, neurophysiological brainstem, or cerebral hemispheric monitoring. In this critical review, we discuss the ascending arousal system, brain herniation, and shortcomings of our current management including the neurological exam, intracranial pressure monitoring, and neuroimaging. We present a rationale for the development of nurse-friendly-continuous, automated, and alarmed-evoked potential monitoring, based upon the clinical and experimental literature, advances in the prognostication of cerebral anoxia, and intraoperative neurophysiological monitoring.

Modified brain stem auditory evoked potentials in patients with intracranial mass lesions.

The authors report their experience utilizing a recently described rapid rate, binaural click and 1000-Hz tone burst modification of the brain stem auditory evoked potentials (BAEP), modified (MBP), in 27 symptomatic patients with non-brain stem compressive space-taking cerebral lesions (22), hydrocephalus (4), and pseudotumor cerebri (1).  Many presented with clinical signs suggestive of increased intracranial pressure (ICP) and focal neurological deficits. The cerebral lesions, mostly large tumors with edema, had very substantial radiological signs of mass effect. Fourteen patients were also studied following surgical decompression. A number of significant changes in the wave V and Vn latency/intensity and less so amplitude/intensity function was found in the 27 patients, compared to normal volunteers, as well as those studied pre- and postoperatively. Similar MBP changes had been noted in normal volunteers placed in a dependent head position. Possible mechanisms to explain these findings are discussed.  The MBP methodology shows promise and further development could make neuro-intensive care unit monitoring practical.

Modified brainstem auditory evoked responses in patients with non-brainstem compressive cerebral lesions.

The brainstem auditory evoked response (BAER) is sensitive to pontomesencephalic integrity, transtentorial brain herniation, and at times increased intracranial pressure (ICP). The authors report their experience utilizing a recently described rapid rate, binaural, click and 1,000-Hz tone-burst modification of the BAER (MBAER) in 22 symptomatic non-trauma patients with non-brainstem compressive space-taking cerebral lesions. The majority presented with mild to moderate clinical signs suggestive of increased ICP, and focal neurological deficits. The cerebral lesions, mostly tumors (17), averaged 4-5 cm in diameter, with radiological signs of mass effect such as flattening of the sulci, midline shift, and narrowing of the basal cisterns. A number of significant changes in Wave V and V (n) latency and less so amplitude were found in patients compared with age-matched normal volunteers, as well as those again studied after surgical decompression. Similar MBAER changes had been noted in normal volunteers placed in a dependent head position. Possible mechanisms to explain these findings are discussed. The methodology shows promise and if combined with automated peak recognition could make Neuro ICU monitoring practical.

Brainstem auditory evoked potentials--a review and modified studies in healthy subjects.

The authors review the brainstem auditory evoked potential (BAEP), and present studies on 40 healthy subjects. In addition to the conventional click evoked BAEP, three modified BAEP examinations were performed. The modified BAEP tests include a 1,000 Hz tone-burst BAEP, and more rapid rate binaural click and 1,000 Hz tone-burst BAEPs-each of the last two studies performed at four diminishing moderate intensities. In addition to the usual parameters, the authors examined the Wave V to Vn interpeak latency, and stimulus intensity versus Wave V latency and amplitude functions in the rapid rate binaural studies. Studies were also repeated on healthy subjects in a dependant head position in an attempt to increase intracranial pressure. Discussion centers on the BAEP, its current utility in medicine, unique neurophysiology, and literature support that the above modifications could increase the practicality of the test in patients at risk with intracranial lesions and perhaps improve the feasibility for real-time continuous or frequent monitoring in the future.

A newly described ictal pattern: the initial ictal slow shift.

This report deals with a newly described ictal pattern, called the initial ictal slow shift (IS)2. This pattern may be seen in subdural records as the first sign of an ictal event, occurring before the later typical rhythms of a seizure state appear. A positive shift, very similar in appearance from one seizure to another, usually lasted for 1-2 sec, followed by a negativity for 7-9 sec that included the typical rhythmical discharges. At times, a negative shift occurred first, seen up to 15 mV very high in amplitude, for a few seconds before the typical ictal rhythms were seen. Scalp records may also demonstrate slow shifts, and examples are shown of the typical 3/sec bilateral spike and wave (S+W) complexes of absence seizures. A slow shift occasionally appeared 1 sec before the onset of these complexes, but more often a few seconds after the onset. Finally, after the end of the S+W complexes, a positive shift, for as long as 5-6 sec may occur, up to 600 microV in amplitude. These shifts could relate to data showing that patients are not really back to a normal responsiveness for at least 5 sec after the end of the S+W complexes (see Discussion).

EEG in seizure prognosis: association of slow wave activity and other factors in patients with apparent misleading epileptiform findings.

Our previous study showed that patients with many spikes in their EEGs generally have uncontrolled seizures and those with no or rare spikes have controlled attacks. However, exceptions do exist, and this study was designed to determine what other aspects in the EEG could lead to the proper prognosis with these exceptions, rather than to an incorrect one. Two groups were assembled: 150 patients with 674 EEGs with controlled seizures and 150 patients with 804 EEGs with uncontrolled attacks. Our data showed that the presence or absence of a slow wave abnormality usually led to a proper prognosis in these exceptional cases. The absence of any slow wave abnormality, but with many spikes was usually associated with controlled attacks and the presence of slowing, especially with delta slow waves, but without spikes, was more often seen in patients with uncontrolled attacks. The change in the number of spikes over time also led to a more accurate prognosis.

The relationship between bilateral spike and wave complexes and focal discharges in patients with partial epilepsy.

The goal of this study was to investigate in patients with partial epilepsy the relationship between bilateral spike and wave (BSW) complexes of a generalized epilepsy and the focal spikes of partial epilepsy. For the study 300 patients were collected, all with focal epilepsy on their last hospital visit: 150 were well controlled (C) and 150 were uncontrolled (U), and the number of EEGs was 674 in the C and 804 in the U groups. BSW were seen at some time in 25% of all patients, more often in the U than C patients, especially the irregular 3/sec form. The bilateral complexes at times appeared at the onset of the epilepsy, usually at the same time with focal discharges, mainly from temporal or frontal areas. The U patients showed these complexes at a younger age than the C group and continued to be seen often into the 30s, occasionally into the 60s age group. The other presentation of the BSW was years after the onset of the focal discharges, usually temporal or frontal in location and more often seen in the U than C group. The U group showed spikes, many in number as active foci, more often than the C group. The discussion deals with the possibility that these bilateral spike and wave complexes may represent a reflection of a lowered threshold to a seizure.

Factors in the interictal record predicting an ictal episode: a case study.

This report deals with a patient with intractable seizures, who had 64 subdural electrodes implanted onto the left frontal and temporal cerebral cortex in anticipation of probable seizure surgery. One specific region on the left frontal lobe proved to be the focus for both the interictal spikes and also for the ictal activity. Our goal was to determine what electrical characteristics in the interictal record predicted the ictal episodes. The number of interictal spikes and also the amount of fast activity (15-128/sec) progressively increased before each of the 5 ictal episodes; an analysis showed that the number of spikes and their frequency proved the more significant variable. One other characteristic that changed before the ictal episodes was a great decrease in the interval between spikes as an example of a diminishing variability or increasing periodicity. Thus, the important factors in the interictal record that lead to an ictal event are the number of spikes, the amount of fast activity and the decreasing variability between the spikes.

The EEG profile of patients with uncontrolled vs. controlled seizures.

The goal of this study was to provide an EEG profile of patients (150) with uncontrolled (U) seizures, in contrast with those (150) with controlled (C) attacks. In the U group 804 EEGs were done and in the C group 674 were performed, all with both waking and sleep recordings; the range of EEG records on a given patient was 2-23. The number of spikes and the amount of abnormal slowing was quantified in each record. Two different peaks of age were evident, appearing at 10-19 yrs and 40-49 yrs. The number of patients with a spike discharge on the first EEG was 64% in the C and 92% in the U group with an increasing incidence to 83% (C) and 100% (U) in later records. If spikes were absent in the first EEG in the C group, the majority showed only rare discharges later. The spike profile of the U patient initially was that 1/2 showed a typical number of spikes and nearly 1/2 many or very many spikes. Over time a decrease was seen in those with many-very many discharges, resulting in an increase with a typical number. Still later, a reversal occurred in the U patients with an increasing number with many or very many spikes. The slow wave profile of the U patient was that 2/3 showed some abnormal slow waves on the first record, increasing to 100% in later records. The increase was from delta, not theta activity. The spike profile of the C patient was that a typical number of spikes was seen at first in nearly 1/2, but only a small minority showed many-very many discharges. The slow wave profile for the C patient was that theta, not delta waves, increased in time. The (median) time between a unilateral spike discharge to a bilateral discharge was 4-5 yrs, and the U group much more often than the C group showed this change to bilateral spikes. The time between unilateral to bilateral slow waves varied between 4-9 yrs.

Focal seizures and EEG: prognostic considerations.

The goal of this study was to determine whether the EEG could predict if patients with focal seizures would eventually be uncontrolled (U), more than two seizures per month, or be controlled (C), fewer than two seizures per year. Using these latter criteria, U and C patients were randomly selected from our files, 150 in each of these two groups; 804 EEGs were found in the U and 674 in the C group. Excluded were patients with generalized epilepsy and also the benign epilepsies of childhood. Age was an important factor since patients 5-18 yrs old were more often under good control (C group), and those 21-48 yrs of age were more often under poor control (U group). With rare exceptions, focal spikes and focal slow waves in every area were much more often seen in U patients than C patients. No spikes or rare spikes appeared especially in the controlled patients, and many or very many spikes in the uncontrolled patients, mainly on the first or second EEG. No slow waves or a mild degree of slowing was seen especially in the C patients, while greater degrees of slow wave abnormalities were noted much more often in the U patients. For conditions to identify the C group, the best predictors were no spikes or rare spikes, especially on the first or second EEG, properly identifying two-thirds of the C patients and misidentifying only one-fourth of the U group. To identify the U patients on any EEG, many or very many spikes at any location or frontal spikes correctly designated a U patient in 84%, but incorrectly predicted a C patient as uncontrolled in 29%. For the first or second EEG, these values were 61% and 21%. Thus, the EEG, especially by its first or second record, can predict well the probable future of the uncontrolled patient, so that extraordinary means may be instituted early to avoid a deteriorating condition. When complete EEGs are done with sleep records and the results are quantified, reasonable prediction of eventual outcome can usually occur that is much more timely than waiting over 9 yrs, using only clinical data.

Epileptic nystagmus and its possible relationship with PGO spikes.

A simultaneous video-EEG on a waking 6-year-old male revealed rapid horizontal and then vertical eye movements and 10 sec later showed ictal rhythms maximal on the occipital areas, quickly spreading to all other areas. A second ictal event during wakefulness was very similar to the first. During sleep interictal discharges were seen from the right frontal-temporal area and one more ictal event was noted. This latter seizure in the NREM sleep record did not show any eye movements, but showed ictal activity on the right frontal-temporal area, which later became generalized. We propose that the interictal discharges on the right frontal-temporal area likely arose from the amygdala, which activated the pontine nuclei responsible for PGO (ponto-geniculo-occipital) spikes and the rapid eye movements seen in our patient. The PGO spikes activated the occipital areas, which then showed clear ictal rhythms to complete the sequence of events. This case demonstrates a sequence of rapid eye movements without ictal patterns, followed by seizure rhythms, but may still be an example of "epileptic nystagmus," assuming that the eye movements arose from an ictal activation of the deep subcortical portion of the PGO system.