A comparison of subdermal wire electrodes with collodion-applied disk electrodes in long-term EEG recordings in ICU
Introduction
Continuous electroencephalogram (cEEG) monitoring has been proven useful in the intensive care unit (ICU) for the evaluation of epileptic seizures, arterial vasospasm, assessing effectiveness of therapy, determining the depth of sedation and other physiological changes in brain function that could indicate the development of life-threatening or unstable conditions (Young et al., 1996, Claassen et al., 2004, Vespa et al., 1997, Young and Doig, 2005, Vespa et al., 2002). However, the ICU is a hostile environment for cEEG: patients are acutely ill, unconscious, frequently moving or being moved, often perspiring and febrile; there are numerous sources of electronic interference. Artifacts are frequent, often unique, difficult to recognize and occur without the continued presence of an EEG technologist or electroencephalographers (EEGer) (Young and Campbell, 1999). These patients usually also require frequent imagining which currently require the removal and then replacement of traditional collodion-applied scalp disc electrodes (SDE).
The most crucial and vulnerable component of EEG recording is the scalp electrode. Electrode artifacts are common in the cEEG of patients in the ICU and may occur early. Such artifacts may preclude adequate interpretation of cEEG or lead to misleading diagnoses and interventions (Young and Campbell, 1999). Recently, developed subdermal wire electrodes (SWE) maintain good recording characteristics and stable impedances for 6–7 days or more (Ives, 2005). They have been used successfully for prolonged ECG monitoring in experimental animals during magnetic resonance imaging (Mirsattari et al., 2005). A similarly designed chronic sphenoidal electrode was developed in the early 1970s for recording from the foramen ovale area and was extensively used to evaluate patients with focal seizures (Ives and Gloor, 1977, Ives and Gloor, 1978). The purpose of this study was to compare the performance of SWE during cEEG with SDE in comatose patients in the ICU.
Section snippets
Methods
Comatose patients (Glasgow Coma Scale score of <8) with acute structural brain lesions who were admitted to the ICU at Sunnybrook and Women's Hospital in Toronto and clinically eligible for cEEG were enrolled in this study. Moribund and brain dead patients were excluded. This project was approved by the hospital's ethics review board and informed consent was obtained from the substitute decision makers of the study participants. The enrolled patients were studied within 48 h of their ICU
Results
Ten patients were studied; all were males between 15 and 75 (mean 45) years. Causes of coma were head injury (6 cases), anoxia-ischemia due to cardiac arrest (two cases), intracerebral hemorrhage (one case) and coma following cardiac surgery with cardiopulmonary by-pass (one patient).
EEGs showed various degrees of slowing in the theta (>4 but <8 Hz) and delta (≤4 Hz) frequency ranges, asymmetries, suppression that were equally well captured on both recordings. Spikes were seen in only two
Conclusions
SWEs were superior to collodion-applied SDEs for cEEG in the ICU, both for 60 Hz and more marked, persistent artifacts. Electrode artifacts with SDE appeared early and were numerous. These were more common in the ICU than anticipated from cEEG from an epilepsy monitoring unit, probably because comatose patients perspire more and, as they are unconscious, do not protect electrodes or wires when they move spontaneously or are passively moved by the care givers. This study examined the ‘worse case
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