Why do some people vomit blood after surgery?

Post-surgical hematemesis (vomiting blood) occurs for various reasons, not all of them serious or grave. Blood is very irritating to the stomach and upper GI tract, and the presence of even small amounts can cause vomiting. Post-surgical drainage of blood into the GI tract does occur and is frequently controlled with the use of nasogastric tubes to keep the irritation to a minimum. Medications can also be used to mitigate vomiting in post surgical situations. If a patient vomits more than a little bit of blood, then special attention needs to be paid to assess whether it is a sign of hemorrhage which would require more surgery to correct. Even a small bleed, over time, can lead to anemia and have an impact on the patient's ability to clot. Any time a patient vomits blood, it needs to be addressed with his or her doctor.