What is the primary cause of lethargy in infants with excessive jaundice?

Lethargy in infants with excessive jaundice is primarily caused by high bilirubin levels. Jaundice occurs when there is an excess of bilirubin in the bloodstream, which can lead to elevated levels that may affect the infant's central nervous system. When bilirubin levels rise significantly, they can cross the blood-brain barrier and result in conditions such as kernicterus, potentially causing neurological impairment. This neurological impact can manifest as lethargy, where the infant becomes unusually drowsy or unresponsive. Monitoring and managing bilirubin levels is crucial in preventing complications arising from hyperbilirubinemia, thereby understanding its direct correlation with lethargy in affected infants.

While other conditions such as low blood sugar, dehydration, and hypoxia can also lead to lethargy in infants, they are not the primary cause associated specifically with excessive jaundice, which is closely tied to high bilirubin levels.