Neonates may have electrical seizures (ES) that are clinically undetected. To identify such infants, 27 infants were monitored with continuous EEG because they were considered to be at high risk: 16 with perinatal asphyxia (5 min Apgar score ≤5 and/or cord pH≤7.2 and continuing lethargy at 2h), of which 11 had suspected clinical seizures (szs) or abnormal movements; 8 with suspected clinical szs without asphyxia; 1 with unexplained apnea at term; 1 with meningitis; 1 with cerebral anomalies. Monitoring continued for 6h-24h(mean 20h) if no ES or 13h-26h (mean 21h) after the last ES. ES were treated with phenobarbital (up to 40 mg/kg) or lorazepam (0.1 mg/kg, up to 3 doses/8h); the second drug was added if ES continued. 13 of the 27 infants had no ES. Of these, 6 had already received anticonvulsant for suspected clinical szs before monitoring; 3 with suspected clinical szs without ES were not treated with anticonvulsant. 14 infants with ES were monitored for a total of 21h-97h (mean 45h) during which 4-226 (mean 54) ES were recorded. Clinical correlates were seen for fewer than 10% of their ES and 5 of the 14 had no clinical szs noted. 5 had more than 10 clinically inapparent ES per hour. 2 of 6 treated with phenobarbital went on to lorazepam; 4 of 9 treated with lorazepam went on to phenobarbital. In 2 infants, multiple ES continued without clinical correlates despite full doses of both drugs that stopped after loading doses of phenytoin. Clinical ascertainment of neonatal seizures is difficult. Continuous EEG monitoring in high risk neonates allows detection of abnormal cortical electrical activity that is not apparent clinically. Animal studies indicate that frequent ES are deleterious to the developing brain. The frequency and duration of clinically undetected ES in neonates and their resistance to traditional anticonvulsant therapy have not been adequately emphasized.

We appreciate the support of The Dorothea Haus Ross Foundation, the Wyeth Pediatric Neonatology Research Fund, and the Neurophysiology Lab at Strong Memorial Hospital.