Heat a thin layer of oil in a large, deep pan over medium heat. Cook the sausage until deeply browned on all sides, then remove it from the skillet.
Cook the shrimp until pink on both sides in the remaining pan grease, adding more oil if needed. Set the shrimp aside.
Melt the butter in the same pan, scraping up any browned bits from the bottom.
Fry the bell peppers, celery, onion, and garlic for about 5 minutes until softened.
Stir the tomato paste into the vegetables and cook for 3-5 minutes until it starts to stick to the bottom of the pan.
Deglaze the pan with white wine, then stir the pan contents and bring them to a simmer. Cook the wine for about 5 minutes until almost all the liquid is reduced, then stir in the chicken broth.
Once the broth is simmering, add the cream cheese, stirring until completely melted.
Stir in the heavy whipping cream, Cajun seasoning, and parmesan.
Toss the cooked fettuccine with the sauce, then add the sausage and shrimp back to the pan and stir just long enough to reheat the proteins.
Season the dish with salt to taste, stir in the parsley, and serve hot.