Decrease In EEG Activity Research Articles

Common patterns of EEG reactivity in post-anoxic coma identified by quantitative analyses

ObjectiveDescription of typical kinds of EEG reactivity (EEG-R) in post-anoxic coma using a quantitative method. MethodsStudy of 101 out-of-hospital cardiac arrest patients, 71 with good outcome (cerebral performance category scale ≤ 2). EEG was recorded 12–24 hours after cardiac arrest and four noxious, one auditory, and one visual stimulation were applied for 30 seconds each. Individual reference intervals for the power in the delta, theta, alpha, and beta bands were calculated based on six 2-second resting epochs just prior to stimulations. EEG-R in consecutive 2-second epochs after stimulation was expressed in Z-scores. ResultsEEG-R occurred roughly equally frequent as an increase or as a decrease in EEG activity. Sternal rub and sound stimulation were most provocative with the most pronounced changes as an increase in delta activity 4.5–8.5 seconds after stimulation and a decrease in theta activity 0.5–4.5 seconds after stimulation. These parameters predicted good outcome with an AUC of 0.852 (95 % CI: 0.771–0.932). ConclusionsQuantitative EEG-R is a feasible method for identification of common types of reactivity, for evaluation of stimulation methods, and for prognostication. SignificanceThis method provides an objective measure of EEG-R revealing knowledge about the nature of EEG-R and its use as a diagnostic tool.

T68. The kind of EEG reactivity assessed by quantitative analyses may predict good and poor outcome in comatose neurosurgical ICU patients

EEG reactivity is defined as a change in frequency or amplitude upon stimulation. However, knowledge about the kind of EEG changes to different external stimulations and their relation to prognosis in comatose patients is sparse. This is despite the fact that EEG reactivity often is regarded as an important factor in outcome prediction and may influence decisions on when to stop life-sustaining therapy. In this study we aimed to quantitatively describe EEG changes in comatose neurosurgical patients due to standardised stimulations and relate the changes to outcome. A standardised stimulation protocol comprising four different pain stimuli (squeezing the nail-side with a pen in both upper limbs and one lower limb and sternal massage), one auditory stimulation (clapping) and one visual stimulation (eye opening) was used. Stimuli were applied for 30 s preceded by a resting period of at least 2 min. Patients were 39 comatose (Glasgow coma scale ⩽8) neurosurgical intensive care unit patients monitored with EEG because they did not wake up as expected. EEG power in the delta, theta, alpha, and beta band was calculated in the first 2, 5, 10, 15, 20, and 30 s of the stimulation epochs and in similar time intervals in the preceding resting epochs. EEG reactivity was quantified as the power measured in z-scores relative to average power of six resting epochs. Outcome was measured after 3 months on the Glasgow Outcome Scale. Significant reactivity was present in 848 out of 5348 analysed epochs (15.9%). Reactivity as an increase in EEG activity was more common (13.4%) than reactivity as a decrease in EEG activity (2.5%). Pain, without any difference between the four stimulation methods, was the most provocative stimulation type (20.4%) followed by sound (8.7%) and eye-opening (6.7%). Increase in EEG activity was related to poor outcome (specificity 100% (CI: 52–100%); sensitivity of 39% (CI: 23–58%)), was more common (13.4% of tests), and grew continuously during the 30-s stimulation epoch. Decrease in EEG activity was related to good outcome (specificity 100% (CI: 87–100%); sensitivity 33% (CI: 6–76%)), was rarer (2.5%), and peaked after 10–15 s of stimulation. Absence of reactivity did not predict poor outcome very well (specificity of 33% (CI: 6–76%); sensitivity 61% (CI: 42–77%)). Grand average analyses revealed that discrimination between good (n = 6) and poor (n = 33) outcome was best for pain stimulation in the theta and alpha bands 15 s after stimulation and for sound stimulation in the theta and alpha bands about 5–10 s after start of stimulation, while eye-opening did not discriminate. Knowledge about different kinds of EEG reactivity and their relation to outcome comprise an important step towards the development of a more objective, reliable and standardised procedure for evaluation of EEG reactivity.

The Nature of EEG Reactivity to Light, Sound, and Pain Stimulation in Neurosurgical Comatose Patients Evaluated by a Quantitative Method.

EEG reactivity (EEG-R) is regarded as an important parameter in coma prognosis but knowledge is sparse on the nature of EEG changes due to different kinds of stimulation and their prognostic significance. EEG-R was quantified in a study of 39 comatose neurosurgical patients. Six 30-second standardized visual, auditory, and painful stimulations were applied. EEG-R in the delta, theta, alpha, and beta band was normalized in z-scores as the power of a stimulation epoch relative to average power of 6 resting epochs. Outcome measure was 3 months Glasgow Outcome Scale. Increase in EEG activity was related to poor outcome, was more common (13.4% of tests), and grew continuously during the 30-second stimulation epoch. Decrease in EEG activity was related to good outcome, was rarer (2.5%), and peaked around 15 seconds. Pain was the most provocative stimulation (20.4%) followed by sound (8.7%) and eye-opening (6.7%). Discrimination between good (n = 6) and poor (n = 33) outcome was best in the theta and alpha bands for pain stimulation in the first 10-20 seconds and for sound stimulation in the first 5 to 10 seconds, eye-opening did not discriminate. Increase in activity predicted poor outcome with a high specificity 100% (CI = 52%-100%) and a modest sensitivity of 39% (CI = 23%-58%). Decrease in activity predicted good outcome with a high specificity of 100% (CI = 87%-100%) and a modest sensitivity of 33% (CI = 6%-76%). This quantitative study reveals new knowledge about the nature of EEG-R, which contribute to the development of more reliable and objective clinical procedures for outcome prediction.

Increased electroencephalographic gamma activity reveals awakening from isoflurane anaesthesia in rats

Animal studies often require reliable measures for anaesthetic drug effects. Lately, EEG-based depth of anaesthesia estimation has been widely applied to rat models. This study investigated the reliability of different EEG spectral properties in revealing awakening from isoflurane anaesthesia in rats. Adult Wistar rats with previously implanted frontal epidural electrodes were anaesthetized using isoflurane. The anaesthesia was slowly lightened until awakening, as observed by the first spontaneous movement, after which anaesthesia was induced again by increasing the isoflurane concentration. EEG was recorded during the recovery and induction periods, and the spectrograms and 23 quantitative spectral parameters used in the depth of anaesthesia estimation were calculated from the signals. The awakening was accompanied by a decrease in EEG activity at frequencies below 25 Hz, while the activity at higher frequencies (25-150 Hz) was increased. Whereas the behaviour of parameters used to measure activity in the lower frequencies was subject to variability between animals, the increase in higher frequency activity was more consistent, resulting in a statistically significant change in the relative gamma power parameters at the moment of awakening. The increase in frontal relative gamma activity, especially in the 50-150 Hz frequency band, seems to be the most reliable EEG indicator for the awakening of a rat from isoflurane anaesthesia. A number of other spectral measures can also be used to detect this event. However, the role of gamma frequencies in the performance of these parameters is crucial.

Temperature Effects on the Electroencephalogram

.The normal range of oral temperatures in humans varies from 92.2° F (36.2° C) to 99.0° F (37.2° C). Changes in body temperature can be directly induced by external factors, or may result from internal processes, i.e. infection or loss of temperature control. The EEG findings in hypo- and hyperthermia reflect not only temperature effects but also other processes that are happening concurrently. The Harvard criteria for “brain death” require a body temperature of at least 90° F (32.2° C) although cerebral activity has been recorded at much lower temperatures. Hypothermia is used clinically to protect the brain during decreased or absent cerebral circulation, usually during cardiac surgery. Hyperthermia can also cause a decrease in EEG activity, although not as dramatic as that seen with hypothermia. Hyperthermia is used clinically in oncology as an adjunct to chemotherapy.