Long term electroencephalography in preterm neonates: Safety and quality of electrode types
Introduction
Seizures in preterm neonates have been reported with an incidence ranging between 3.9% and 48% (Hellstrom-Westas et al., 1985, Scher et al., 1993, Vesoulis et al., 2014, Lloyd et al., 2017). Seizure incidence varies with the EEG modality utilized- amplitude-integrated EEG (aEEG) versus conventional EEG. Early life seizures in sick premature neonates portend both poor short and long term outcomes. Seizures in extremely low birth weight neonates were associated with short term morbidities such as severe intraventricular hemorrhage, sepsis, meningitis and cystic periventricular leukomalacia (Davis et al., 2010). Long-term adverse outcomes (cerebral palsy, developmental delay and epilepsy) were reported in preterm neonates with confirmed neonatal status epilepticus (Scher et al., 1993, Pisani et al., 2016), and decreased language performance at 2 years of age was noted in patients with seizures detected in the first three days of life (Vesoulis et al., 2014). To better define the prevalence and significance of seizures in this population, long-term conventional EEG recording in preterm neonates is gaining widespread interest and increasingly being clinically utilized.
Full montage EEG (full scalp coverage) has significant advantages over amplitude-integrated EEG. aEEG is a bedside neuromonitoring tool that records EEG signal using one or two channels placed in the centro-parietal areas of the newborn’s head (Toet and Lemmers, 2002). aEEG was found to have lower sensitivity and specificity in seizure detection, in newborns (Hellstrom-Westas, 1992, Toet et al., 2002, Rennie et al., 2004, Shah et al., 2008). The time-compressed nature of aEEG tracings and the centro-parietal location of the electrodes, may lead to reduced detection of seizures with low amplitude, brief duration (Hellstrom-Westas, 1992) and focal seizures distant from the aEEG electrodes (Rakshasbhuvankar et al., 2015).
The use of full montage EEG electrode array on a preterm neonate can be challenging due to the small head size and the vulnerability of the premature skin. Additionally, for long term EEG studies, the integrity of the skin must be balanced against EEG recording quality. At our institution, we currently utilize gold cup electrodes for all clinical studies. With application of gold cup electrodes, first a gentle cleansing gel is used to remove debris from the skin, and conductive paste and paper tape are used to fix the electrodes in place. Collodion, used to glue down the gold cup electrodes in most long-term EEG studies, is not used in the preterm population due to the fragility of the preterm scalp, which limits the stability of the gold cup electrodes, especially in a humidified and warm environment such as in an incubator.
The skin of extremely low birth weight preterm neonates is not fully developed compared to term newborns with an immature stratum corneum, which poses problems in the care of the preterm skin. The stratum corneum which is the outermost layer of the epidermis develops in the third trimester of pregnancy, and is responsible for protection against microorganisms, reducing transepidermal water loss and minimizing absorption of toxins from topical products (Ness et al., 2013). Unfortunately, the preterm skin lacks this protective layer, making it fragile and easily damaged. The removal of tape or adhesive dressings can be harmful to the preterm skin due to weak epidermal-dermal junctions, and decreased elastic fibrils (Ness et al., 2013). This is why it is recommended to decrease the use of adhesives in this population, and to replace with hydrogel electrodes when available (Lund et al., 2001).
Hydrogel electrodes have been shown to be an adequate alternative to gold cup and subdermal needles in aEEG recordings when used with adequate skin preparation (Foreman et al., 2011). They have the advantage of increased adhesion to the preterm skin, especially in a humidified environment, and they have a flat surface, decreasing pressure points on the skin when the neonate’s head lies on electrodes and wires. In addition, hydrogel electrodes are sterile and disposable, but not reusable.
While evaluating the frequency of seizures in the preterm population, we hypothesized that hydrogel electrodes can be used instead of the gold cup electrodes for full EEG recordings and they are non-inferior compared with gold cup electrodes in the recording quality and maintenance with better skin tolerance. Our objectives were to compare the recording safety and quality between the gold cup and hydrogel electrodes using a study design that directly compares the two electrode types in each neonate.
Section snippets
Study population
All newborns born at ≥23 weeks and ≤30 weeks of gestational age and admitted to the neonatal intensive care unit of Saint Louis Children’s Hospital, were eligible if the following inclusion criteria were met: 1-aged less than 24 h of age, and 2-no known congenital anomalies or genetic syndromes were identified. These neonates were not recruited for neurological risk or clinical indications, rather this population reflects the typical preterm NICU population. Parents of eligible neonates were
Study population
Our study included 50 neonates with mean gestational age (GA) of 27 (±1) weeks. Mean birthweight was 1100 (±260) grams. Twenty-six subjects were females (52%) and 26 (52%) subjects were African-American. Four neonates expired during their hospital stay. One of the subjects died within the first 24 h before any electrodes were applied. Death was attributed to extreme prematurity, severe IUGR and respiratory distress. Two other patients expired due to necrotizing enterocolitis at two weeks of
Discussion
Our study was a prospective trial and the first to directly compare the safety and quality of hydrogel and gold cup electrodes for recording long term conventional EEG in preterm neonates.
We performed 50 EEG studies in a group of preterm neonates evaluating hydrogel and gold cup electrodes in terms of skin irritation and safety of either type in continuous EEG studies. No adverse effects were noted with either type, demonstrating that hydrogel electrodes can be used safely as an alternative to
Conclusions
Full montage EEG studies were well tolerated in preterm neonates with either electrode type. Hydrogel electrodes are a reasonable alternative to gold cup electrodes for long-term EEG monitoring in preterm neonates. The hydrogel electrodes showed no serious adverse skin irritation along with easy application and appropriate longevity showing acceptable impedances throughout EEG monitoring. All of these factors make hydrogel electrodes a more than acceptable alternative compared to standard gold
Sources of support
1. The Gerber Foundation.
2. Washington University Institute of Clinical and Translational Sciences KL2 Training Program (NIH/NCATS KL2 TR000450).
3. Neurological Sciences Academic Development Award at Washington University School (5 K12 NS001690-19).
Conflict of interest
The authors have no potential conflicts of interest to disclose.
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