Anything splanchnic affects or refers to your guts, or internal organs, especially the ones in your abdomen. A splanchnic pain, for example, might be felt in your stomach.
The adjective splanchnic isn't very common, though it's used sometimes in medical terminology, as in the splanchnic nerve, which connects to the digestive tract. When you see splanchnic, you know it's referring to a person's innards or organs. The original meaning of splanchnic is "pertaining to the viscera," from a Greek root, splankhnon, and its plural form, splankhna, "the entrails or innards."