Pathophysiology

1. Gastric Mucosal Blood Flow and Ischemia

The gastric mucosa is highly vascularized, and its integrity is maintained by a balance between aggressive factors (like acid and pepsin) and defensive factors (like mucus, bicarbonate, and blood flow). The primary cause of stress ulceration is a disruption in this balance, with a significant factor being decreased gastric mucosal blood flow leading to ischemia.

• Hypovolemia: Reduced blood volume can lead to decreased perfusion of the gastric mucosa.
• Reduced Cardiac Output: Conditions like heart failure or shock can reduce the heart’s ability to pump blood, leading to decreased blood flow to the stomach.
• Release of Proinflammatory Mediators: Inflammatory mediators, such as cytokines, can cause local inflammation and damage to the gastric mucosa.
• Increased Catecholamine Release: Stress, injury, or illness can lead to the release of catecholamines, which can cause vasoconstriction and reduce blood flow to the gastric mucosa.
• Visceral Vasoconstriction: In response to stress or shock, the body may divert blood away from the visceral organs, including the stomach, to prioritize vital organs like the brain and heart.

2. Impaired Mucosal Barrier

• The gastric mucosa has a protective barrier composed of mucus and bicarbonate. This barrier prevents the back-diffusion of hydrogen ions and protects the mucosa from the aggressive action of gastric acid.
• Reduced Mucus and Bicarbonate Production: Critically ill patients may have impaired mucus and bicarbonate production, weakening the mucosal barrier.
• Impaired Gastric Emptying: Delayed gastric emptying can increase the contact time between the gastric acid and the mucosa, leading to potential damage.
• Acid Back-Diffusion: When the mucosal blood flow is compromised, it can lead to back-diffusion of acid into the mucosa, causing injury.
• Reperfusion Injury: If blood flow is restored after a period of ischemia, the sudden influx of oxygen can generate reactive oxygen species, leading to oxidative damage to the mucosa.

3. Resultant Damage

The combination of reduced mucosal blood flow, impaired mucosal barrier, and the aggressive factors allows for damage from gastric acid, bile, and digestive enzymes. This can lead to superficial erosions in the mucosa within hours of an acute illness or injury. If not addressed, these erosions can deepen, leading to ulcerations and potentially significant bleeding.

Stress ulcers are a multifactorial condition, with ischemia and impaired mucosal defense playing pivotal roles. Understanding the pathophysiology is crucial for healthcare professionals to provide appropriate prophylaxis and treatment to at-risk patients. Given the complexity of the condition and the potential for severe complications, it’s essential to approach patient care with a high level of detail and accuracy.