My Father Who Is 86 Years Old Had Abdominal Surgery

my father who is 86 years old had abdominal surgery last year, a small portion of his small intestine was removed. He then this year developed a hernia in the area, and had hernia repair surgery, BUT now he is not healing, and the surgeon said he has developed a fistula. He has been put on TPN, but is weaker now, and the drainage is pretty heavy at times. What kind of doctor could I go for a second opinion?