Monitoring seizures in critically ill children
Seizure burden in children has been strongly associated with neurological decline, indicating that seizures among critically ill children are not only a biomarker but also an independent contributor to brain injury. Although electrographic seizures are common in encephalopathic critically ill children, most of these seizures are subclinical.
At Mayo Clinic in Rochester, Minnesota, continuous electroencephalography (cEEG) is used to accurately quantify the burden of subclinical seizures and subtle electroclinical seizures among critically ill children. CEEG is available in Mayo Clinic's pediatric, neonatal and cardiac ICUs.
"Between 70 and 80 percent of the seizures we see in the critical care setting are subclinical, and cEEG is the only way we currently have to diagnose them," notes Eric T. Payne, M.D., a consultant in Pediatric Neurology at Mayo Clinic's campus in Minnesota, whose training included a clinical and research fellowship in pediatric epilepsy and neurocritical care. "CEEG allows us to capture and treat subclinical seizures and, conversely, to avoid overtreating children who might be showing clinical signs but aren't actually having seizures."
Dr. Payne and Cecil D. Hahn, M.D., discussed the use of cEEG monitoring among critically ill children at risk of electrographic seizures and status epilepticus in a review published in Current Opinion in Pediatrics in 2014.
Clinical indications for cEEG
In Mayo Clinic's ICUs, cEEG involves the same noninvasive technique used in the inpatient epilepsy monitoring unit. Technicians monitor ICU patients on EEG round-the-clock. Common clinical indications for cEEG in Mayo Clinic's ICUs include:
- Established seizures or status epilepticus, to guide titration of anti-epileptic drug therapy
- Screening for subclinical seizures among patients deemed to be at high risk because of suspected encephalitis, hypoxic-ischemic encephalopathy, traumatic brain injury or stroke
- Screening for seizures among patients who are paralyzed and deemed at risk of seizures
- Characterization of paroxysmal events suspected to represent electrographic seizures
Depending on the underlying causes of their disorders, patients might undergo cEEG for periods ranging from 12 to 24 hours to several weeks.
"Kids under 2 to 3 years of age are at higher risk of seizure," Dr. Payne says. "Once a patient is on EEG, within an hour we can see indications on the readout that tell us the level of risk that patient has for seizing down the line. For example, interictal discharges, or background activity that is slow or discontinuous, might go on to become seizure activity."
In a study published in the May 2014 issue of Brain, Dr. Payne and colleagues found that above a maximum seizure burden threshold of 12 minutes an hour, the probability and magnitude of neurological decline rose sharply. Dr. Payne estimates that roughly 10 percent of children on ICU EEG monitoring at Mayo Clinic have status epilepticus; up to half of those children have entirely subclinical seizures. Clinical indications of seizure are especially difficult to discern in neonatal ICU patients.
"Without cEEG we would miss status epilepticus in a not insignificant proportion of our pediatric patients," he says. "We don't want to miss those high-risk kids."
Quantitative trends analysis
Mayo Clinic uses quantitative EEG trends analysis, which compresses raw EEG readings to show as much as 16 hours of monitoring on a single page. "Within seconds you can identify where the seizures are probably happening," Dr. Payne says. "It doesn't replace the raw data because what might look like a seizure on the trend analysis can turn out to be an artifact when you check the raw reading. But having these trends posted right by the patient's bedside is a very helpful tool."
In a critical care setting, where other major organs are monitored, it is important to monitor the brain as well. "We have shown that prolonged seizure or status epilepticus is bad for the brain," Dr. Payne says. "Seizures are just as bad if they're subclinical, and they cannot be managed in the ICU without EEG."
For more information
Payne ET, et al. Continuous electroencephalography for seizures and status epilepticus. Current Opinion in Pediatrics. 2014;26:675.
Payne ET, et al. Seizure burden is independently associated with short term outcome in critically ill children. Brain. 2014;137:1429.