Hyperventilation activation on EEG recording in children with epilepsy

Indications for epilepsy monitoring in pediatric and adolescent health care

Seizures present in childhood with infinite diversity. History alone may suffice for diagnosis in some cases; more often additional evidence is needed to clarify events of concern. Electroencephalography (EEG) is a primary methodology used for seizure identification and management. Pediatric and adolescent health care providers are increasingly asked to make decisions about when and how to refer patients for eventual monitoring and must then be able to confidently interpret any resulting report(s). Comprehensive literature review was undertaken to provide a succinct and up-to-date overview aimed at general and subspecialty non-neurologist pediatric and adolescent health care providers to not only convey a solid general understanding of EEG and what it entails for patients and their families, but also foster a deeper understanding of the indications for monitoring-and how to interpret documented findings. In plain language this resultant guide reviews EEG basics, provides a crash course in the various types of EEG available, discusses broad indications for epilepsy monitoring, guides counseling and management for patients and their families both before and after EEG, and ultimately aids in the interpretation of both findings and prognosis. This review should allow both primary and subspecialty non-neurologic pediatric and adolescent health care providers to better identify when and how to best utilize EEG as part of a larger comprehensive clinical approach, distinguishing and managing both epileptic and nonepileptic disorders of concern while fostering communication across providers to facilitate and coordinate better holistic long-term care of pediatric and adolescent patients.

Hyperventilation during routine electroencephalography: are three minutes really necessary?

OBJECTIVE

Hyperventilation induces absence seizures in children with absence epilepsy, and routine electroencephalography studies include three minutes of hyperventilation. We studied the duration of hyperventilation required to provoke a first absence seizure to determine whether three minutes of the procedure are indeed necessary.

METHODS

Electroencephalography records of children who experienced absence seizures during hyperventilation were reviewed. The time from hyperventilation onset to a first and further seizure(s) was measured, and the occurrence of absences during the posthyperventilation phase was also noted.

RESULTS

Sixty-two studies were evaluated. Mean time from hyperventilation onset to a first absence was 52 seconds (median 32 seconds). The vast majority (85.5%) had an absence within 90 seconds. Most (68%) children sustained a single event. All eight children with posthyperventilation seizures had experienced at least one event during hyperventilation.

CONCLUSIONS

Our findings suggest that current guidelines for routine pediatric electroencephalography recording requiring three minutes of hyperventilation may not be clinically necessary. We found that the vast majority of children referred for suspected absence seizures experience a seizure less than 90 seconds after hyperventilation onset, and even more so by 120 seconds. Hence, a larger prospective study is warranted to establish more accurate hyperventilation duration parameters. We also suggest that once an absence seizure has been recorded at any time during hyperventilation, this procedure could be stopped, thus reducing the amount of discomfort for the child.

Change in the electroencephalogram delta wave in the frontal cranial region of rats with the hyperventilation

Hyperventilation is one way to cause activation on the electroencephalogram (EEG) to diagnose brain disorders. The hyperventilation is also known to affect on the delta power in EEG. This study divided the total delta wave into low, middle, and high bands corresponding to the wave frequency. The power in these three delta wave bands was examined in the frontal cranial region of adult male Sprague-Dawley rats hyperventilated with ventilation (VE) of 360, 540, and 720 ml/min for 5 min. The control group was ventilated normally with a volume of 160 ml/min. The results show that the relative power of the low delta band in the rats hyperventilated at 360 ml/min VE was significantly increased compared with powers of pre-hyperventilation (p<0.05). The relative power of the middle delta band was not significantly affected by hyperventilation at any VE, and in the high delta band, all of the relative powers were decreased significantly in all hyperventilated rats compared with powers of pre-hyperventilation (p<0.05). We concluded that hyperventilation affects the frontal cranial region, by increasing the low delta band and decreasing the high delta band.

Changes in extracellular neurotransmitters in the cerebrum of familial idiopathic epileptic shetland sheepdogs using an intracerebral microdialysis technique and immunohistochemical study for glutamate metabolism

Intracerebral microdialysis combined with electroencephalographic recordings was performed on 4 dogs of a familial idiopathic epileptic Shetland sheepdog colony to identify the kinds of neurotransmitters responsible for seizure activity. Immunohistochemistry using glutamate (Glu), glutamate transporter (GLT-1 and GLAST), and glutamine synthetase (GS) antibodies was also carried out on the cerebrum of four familial dogs that died of status epilepticus (SE). High values for extracellular levels of Glu and aspartate (ASP) were detected in association with an increased number of spikes and sharp waves during hyperventilation in 3 of 4 the familial epileptic dogs. The values of other amino acids analyzed were not altered in any of the familial epileptic dogs. Immunohistochemically, Glu-positive granules were occasionally found in the perineuronal spaces of the cerebral cortex in 3 of the familial epileptic dogs that died of SE. Immunostains for GLT-1 antibody predominantly decreased in the cerebral cortex and lateral nucleus of the thalamus in all the dogs that died of SE, whereas there were no differences detected in immunolabellings for GLAST and GS antibodies between familial epileptic dogs and controls. These results suggest that an extracellular release of both Glu and Asp may play an important role in the occurrence of seizure activity in this epileptic colony, and that a decreased expression of astrocytic GLT-1 may be related to development of SE.

Effect of carbon dioxide on background cerebral electrical activity and fractional oxygen extraction in very low birth weight infants just after birth

Decreased arterial carbon dioxide tension (PaCO2) results in decreased cerebral blood flow, which is associated with diminished cerebral electrical activity. In such a situation, cerebral fractional oxygen extraction (CFOE) would be expected to increase to preserve cerebral oxygen delivery. This study aimed to determine whether changes in blood gases in infants less than 30 wk' gestation were associated with changes in background electroencephalograms (EEG) and CFOE. Thirty-two very low birth weight infants were studied daily for the first three days after birth. Digital EEG recordings were performed for 75 min each day. CFOE, mean blood pressure and arterial blood gases were measured midway through each recording. EEG was analysed by (a) spectral analysis and (b) manual calculation of interburst interval. Blood pressure, pH and PaCO2 did not have any effect on the EEG. On day one, only PaCO2 showed a relationship with the relative power of the delta frequency band (0.5-3.5 Hz) and the interburst interval. The relative power of the delta band remained within normal limits when PaCO2 was between 24 and 55 mmHg on day one. There was a negative association between PaCO2 and CFOE. The associations between PaCO2 and EEG measurements were strongest on day one, weaker on day two, and absent on day three. The slowing of EEG and increased CFOE at lower levels of PaCO2 are likely to be due to decreased cerebral oxygen delivery induced by hypocarbia. When PaCO2 was higher, there was suppression of the EEG.

Effects of hydration and hyperventilation on cortical complexity

The effects of hydration and hyperventilation on cortical complexity were investigated in a sample of 19 healthy volunteers in a double-blind placebo design using magnetoencephalographic recordings. The subjects were asked to abstain from the intake of liquids 18 h before the study. Spontaneous magnetoencephalograms (MEG) were recorded before and after drinking 750 ml water (WAT group: nine subjects) or saline solution (SAL group: ten subjects) with eyes closed and open and during hyperventilation (HV) with eyes open. The MEG data were analysed using both linear (spectral power) and non-linear (pointwise dimension and largest Lyapunov exponent) algorithms. The prediction that intake of water, because of induced cell swelling, will lead to an increased synchronization and a decreased complexity of the spontaneous MEG during hyperventilation was confirmed. Hyperventilation following the drinking condition produced an increase in all power spectra with a stronger increase of delta and theta power after drinking of water. This synchronization of spontaneous MEG is accompanied by a general significant decrease of cortical complexity, especially after water drinking. Moreover, cortical complexity was inversely related to delta and theta power and partly also to alpha power. The SAL and WAT groups showed different relations between alpha power and dimensional complexity during HV: whereas in the SAL group the correlations between these measures became more negative during HV, they reversed in the WAT group to become positive. The synchronizing effect of hyperventilation, leading to a decrease of cortical complexity, is related in the SAL group to delta, theta and alpha power, whereas in the WAT group only delta and theta activity contribute to a reduction of cortical complexity.

Hyperventilation-induced high-amplitude rhythmic slowing with altered awareness: a video-EEG comparison with absence seizures

PURPOSE

Hyperventilation-induced high-amplitude rhythmic slowing (HIHARS) in children may be associated with clinical episodes of altered awareness. The presence of automatisms has been proposed as a distinguishing feature that helps to differentiate absence seizures from nonepileptic causes of decreased responsiveness. This retrospective, controlled, video-EEG study compared the clinical characteristics of episodes of HIHARS with loss of awareness with those of absence seizures.

METHODS

The database of a tertiary Children's Hospital was searched for patients studied between April 1993 and April 1997 who had at least one episode of HIHARS with loss of awareness. The absence control group was obtained by selecting the next patient, after an HIHARS study subject, who met the following criteria: (a) had at least one absence seizure occurred during hyperventilation in the EEG recording, and (b) had a diagnosis of idiopathic generalized epilepsy. The video-EEG and medical histories of all patients were reviewed and summarized.

RESULTS

We reviewed video-EEG recordings of 77 episodes of HIHARS with loss of awareness from 22 children and 107 absence seizures during hyperventilation from 22 children. Eye opening and eyelid flutter were seen more frequently in absence seizures, whereas fidgeting, smiling, and yawning occurred more frequently during HIHARS episodes. Arrest of activity, staring, and oral and manual automatisms were observed in both groups.

CONCLUSIONS

Automatisms are common in both HIHARS and absence seizures. Yawning, smiling, and particularly fidgeting occur more commonly and eye opening and eyelid flutter less commonly in HIHARS. However, episodes of HIHARS with loss of awareness clinically mimic absence seizures, and these conditions can be distinguished reliably only by EEG.

Effects of water on cortical excitability in humans

The effects of water on cortical excitability, measured using magnetoencephalographic recordings, were investigated in a sample of 19 healthy volunteers in a double-blind, placebo experiment comparing water with saline solution. Spontaneous magnetoencephalogram as well as auditory-evoked magnetic fields were recorded before and after the drinking of 750 mL water (9 subjects) or saline solution (10 subjects) and during and after hyperventilation following the drinking conditions. Hyperventilation was used to enhance the hypothesized synchronizing effect of water on spontaneous magnetoencephalographic activity. In addition, the magnetic fields were measured during a dichotic listening task under attended and unattended conditions. The prediction, that intake of water, because of induced cell swelling, will increase neuronal excitability and lead to an increased synchronization of the spontaneous magnetoencephalogram during hyperventilation was confirmed. Hyperventilation induced an increase of spectral power in all frequency bands particularly theta and delta power after water drinking. Furthermore, there was an increase of magnetic mismatch negativity (MMNm) amplitude in attended conditions and a simultaneous decrease in unattended conditions after water drinking. N1m (magnetic N1 wave) revealed significant changes during experimental conditions: increase after drinking and decrease after hyperventilation in both groups. MMNm for attended conditions showed a high positive correlation with osmolality changes (difference in the mol solute per kg water before and after drinking); N1m and PNm (magnetic processing negativity) as well as MMNm for unattended conditions showed significant correlations with subjective ratings of thirst and mood state.

[Anesthesia for epilepsy surgery]

Epilepsy is rather common, affecting 0.5 to 2% of the population. Numerous patients, particularly those resistant to the antiepileptic therapy, can be surgically treated after a thorough evaluation. Surgery for epilepsy can be carried out either under general or local anaesthesia with sedation. This second approach is reserved for the extirpation of foci localised in motor, sensory or language areas. During the preoperative anaesthetic evaluation, two specific points have to be taken into account: the psychological aspect and the antiepileptic medication. During the procedure, an electrocorticography with or without stimulation may be indicated, particularly when a perioperative stimulation is scheduled. Low doses of volatile agents are chosen, and no curare and large doses of benzodiazepines and barbiturates. Awakening takes place on the operation table for a rapid and reliable neurological evaluation. During procedures performed under local anaesthesia, the anaesthetist must be ready at any time to intubate the patient in order to secure the airway.

Cerebral oxygenation and hemodynamics during hyperventilation and sleep in patients with Rett syndrome

We continuously monitored changes in cerebral oxygenation and hemodynamics in the frontal lobes of six patients with Rett syndrome during the awake state, which is associated with hyperventilation (HV) and breath-holding (BH), and during sleep by near-infrared spectroscopy. We also monitored three adult volunteers during simulated episodes of HV and BH. In patients with Rett syndrome, the oxygenated hemoglobin (HbO2) and total hemoglobin (HbT) decreased significantly during HV and BH in the awake state compared with the sleep state. The HbO2 and HbT decreased gradually in adult volunteers in response to prolonged episodes of HV and BH. Further studies are required to investigate the relationship, if any, between the discovered continuous decreases in HbO2 and HbT during the awake state and the brain damage seen in patients with Rett syndrome.

The development of hemodynamics in the extracranial carotid and vertebral arteries

To investigate the development of hemodynamics in the extracranial carotid and vertebral artery system, a prospective color duplex sonography study was performed in 94 healthy children and adolescents between 3 and 18 y old. Angle-corrected flow velocities and luminal diameters were measured; waveform parameters and flow volumes were calculated. Side-to-side differences of volumetric data were analyzed. In 53 children, an intrasession test-retest flowmetry of the internal carotid and vertebral arteries was performed. From 3 to 18 y old, flow volumes decreased significantly in the vertebral arteries (p < or = 0.01) and increased in the external carotid artery (p < or = 0.0001); the luminal diameter increased in all the carotid arteries (p < or = 0.0001) and remained constant in the vertebral arteries; mean flow velocities declined in the common and internal carotid arteries and in the vertebral arteries (p < or = 0.0001), but increased in the external carotid arteries (p < or = 0.01). Flow volume rate was lower in the right than the left vertebral artery (p < or = 0.0001), and there was no side difference in any of the carotid arteries. The test-retest correlation of volumetric data was high (0.81 < or = r < or = 0.97; p < or = 0.0001). By comparing the reference data presented here with analogous adult data, we were able to delineate the physiologic development of extracranial and cerebral hemodynamics from childhood to adulthood. These data make possible the clinical application of quantitative flowmetry in extracranial cerebral arteries of children and adolescents.

Ictal cerebral perfusion related to EEG in drug resistant focal epilepsy of childhood

OBJECTIVES

To evaluate the EEG changes during seizures in children with drug resistant focal epilepsy who demonstrate hypoperfusion at the "seizure focus" interictally, but no perfusion change during the seizure.

METHODS

Ictal EEG findings of six children with focal epilepsy who demonstrated hypoperfusion on rCBF SPECT after an interictal injection of (99)Tc(m) HMPAO concordant with the seizure focus, but who did not demonstrate rCBF change after an ictal injection (group 1) were reviewed. These were contrasted with the EEG data of six children matched as closely as possible for age, type of epilepsy, and pathology who did show hyperperfusion at the seizure focus on ictal scan when compared with the interictal study (group 2).

RESULTS

The children in group 1 showed slowing of the EEG at the time of the (99)Tc(m) HMPAO injection relative to that seen at the onset of the seizure. Those in group 2 showed rhythmic activity, or sharp waves, or both on EEG at the time of injection. This last change was also seen consistently when the EEG data of a further 13 children who also showed ictal hyperperfusion at the seizure focus were reviewed.

CONCLUSION

Ictal rCBF does not invariably increase at the seizure focus in patients with drug resistant focal epilepsy.