casualty department vs trauma centre

casualty department

noun
  • (also casualty ward) the department of a hospital providing immediate treatment for emergency cases. Called emergency room in North America. 

trauma centre

noun
  • A specialized section of a hospital intended to treat suddenly occurring life-threatening injuries and medical conditions. 

  • A type of hospital with a highly capable trauma department. 

How often have the words casualty department and trauma centre occurred in a corpus of books? (source: Google Ngram Viewer )