Final answer:
The next step for the 8-year old child in the ER should be a CT head scan to evaluate for potential traumatic brain injuries following a car accident, given the low GCS score and scalp laceration.
Step-by-step explanation:
The 8-year old child in the ER who has been struck by a car is presenting with an altered mental status, indicated by the Glasgow Coma Scale (GCS) score of 8T, and has just received a chest tube for a right sided pneumothorax. The child also shows signs of potential blood loss given the reported low hematocrit and hemoglobin levels. Given these findings, particularly the GCS of 8T and the significant scalp laceration, the initial step in further evaluating the child should be a CT head scan. This will help to assess for any intracranial bleeding or other traumatic brain injuries (TBIs) that could be life-threatening and need immediate intervention.