During World War I, he was responsible for the treatment of wounded soldiers at a hospital in Vichy.
Following the end of hostilities, he became head of medical services at the Hôpital de la Charité.
Castaigne felt that a small village environment would be beneficial in raising his other children.
At Paris, he studied under Anatole Chauffard (1855-1932) and Augustin Nicolas Gilbert (1855-1927), and performed investigations involving renal functionality with internist Emile Charles Achard (1860-1944).
His name is also lent to the "Castaigne test", a method for examining the density of urine.