Which of the following is an essential criterion for diagnosing hypoxic-ischemic encephalopathy?

The diagnosis of hypoxic-ischemic encephalopathy (HIE) heavily relies on the presence of metabolic acidosis in fetal arterial blood. This condition is characterized by impaired oxygen delivery to the brain, leading to neuronal injury. Metabolic acidosis, indicated by a low arterial blood pH and elevated levels of lactate, is a direct consequence of insufficient oxygen causing the tissues to resort to anaerobic metabolism. This biochemical change reflects the extent of brain injury and is a critical factor in establishing the diagnosis of HIE.

While evidence of fetal heart rate variability, maternal fever at delivery, and low birth weight can be associated with adverse perinatal outcomes, they do not specifically indicate the presence of hypoxic-ischemic injury to the brain. Therefore, metabolic acidosis remains a cornerstone criterion for diagnosing this particular condition.