From the Research
Gastrointestinal bleeds cause nausea and vomiting primarily due to the presence of blood in the GI tract, which acts as an irritant, stimulating chemoreceptors and triggering the body's natural protective mechanisms. The presence of blood in the stomach or intestines can lead to the activation of the vomiting center in the brain, resulting in nausea and vomiting. This is further supported by the fact that blood is a protein-rich substance that, when broken down, produces compounds that can directly stimulate the chemoreceptor trigger zone in the brain stem, promoting nausea and vomiting 1.
Some key points to consider include:
- The accumulation of blood in the stomach can cause distension, triggering stretch receptors that signal fullness and nausea
- Significant blood loss can lead to hypotension and reduced blood flow to the brain, independently causing nausea and vomiting
- The body attempts to expel the blood through vomiting as a protective mechanism
- In severe cases, the vomited blood may appear bright red or dark like coffee grounds, which is an important diagnostic sign of upper GI bleeding
It's also worth noting that the management of GI bleeds involves assessing the patient's hemodynamic status, risk stratification, and endoscopic diagnosis and treatment, as outlined in the ACG Clinical Guideline: Management of Patients With Acute Lower Gastrointestinal Bleeding 2. Additionally, proton pump inhibitors may be used to reduce the risk of GI bleeding in high-risk patients, as shown in a study on pantoprazole for the prevention of gastrointestinal bleeding in high-risk patients with acute coronary syndromes 3. However, the most recent and highest quality study on this topic is the 2022 Cochrane review on proton pump inhibitor treatment initiated prior to endoscopic diagnosis in upper gastrointestinal bleeding, which found that pre-endoscopic PPI use likely reduces the requirement for endoscopic haemostatic treatment at index endoscopy 1.
Overall, the presence of blood in the GI tract is the primary cause of nausea and vomiting in GI bleeds, and management involves a combination of supportive care, endoscopic diagnosis and treatment, and pharmacological interventions to reduce the risk of bleeding and promote healing.