Comparison of approaches to stress ulcer prophylaxis in hemorrhagic shock

A review of stress-related mucosal disease

OBJECTIVE

To review and summarize the human and veterinary literature regarding stress-related mucosal disease (SRMD) pathogenesis, patient risk factors, and therapeutic options for prophylaxis and treatment.

ETIOLOGY

SRMD is a common sequela of critical illness in human patients. Development of SRMD results from splanchnic hypoperfusion, reperfusion injury, and exposure of the gastric mucosa to acid, pepsin, and bile acids following breakdown of the gastric mucosal defense system. Human patients with the highest risk of stress ulceration include those with respiratory failure necessitating mechanical ventilation greater than 48 h or coagulopathy. Currently, little is known about the incidence and pathophysiology of SRMD in critically ill veterinary patients.

DIAGNOSIS

A presumptive diagnosis can be made in high-risk patient populations following detection of occult or gross blood in nasogastric tube aspirates, hematemesis, or melena. Definitive diagnosis is achieved via esophagogastroduodenoscopy. Lesions are localized to the acid-producing portions of the stomach, the fundus, and body.

THERAPY

Therapy is aimed at optimization of tissue perfusion and oxygenation. Pharmacologic interventions are instituted to increase intraluminal pH and augment natural gastric defenses. Histamine(2)-receptor antagonists, proton pump inhibitors, and sucralfate are the mainstays of therapy. In people, clinically significant bleeding may necessitate additional interventions (eg, packed red blood cell transfusions, endoscopic, or surgical hemostasis).

PROGNOSIS

Mortality is increased in people with clinically significant bleeding compared to those patients who do not bleed. Institution of prophylaxis is recommended in high-risk patients. However, no consensus exists regarding initiation of prophylaxis, preference of frontline drug class, or indication for discontinuation of therapy. The prognosis of veterinary patients with SRMD remains unknown at this time.

Experimental studies on the prediction and prevention of stress ulcers using tonometry, reflectance spectrophotometry and oxygenated perfluorochemicals

The present study investigates whether oxygenated perfluorochemicals protect the gastric mucosa against hemorrhage-induced stress ulceration. The influence of oxygenated perfluorochemicals on both macroscopic and microscopic lesion formation, gastric intramural pH, index of oxygen saturation and index of hemoglobin saturation of the gastric mucosa was studied. To assess the severity of gastric mucosal ischemia, intramural pH was directly measured using a pH sensitive microelectrode and indirectly by utilizing hollow viscus tonometry, and the indices of oxygen saturation and hemoglobin saturation were measured by reflectance spectrophotometry. Oxygenated perfluorochemicals (30 ml/kg/h) significantly protected the gastric mucosa against both gross (lesion index 0.85 +/- 0.2 vs 2.23 +/- 0.31) and microscopic (lesion index 0.52 +/- 0.02 vs 2.04 +/- 0.03) injuries. This protection was associated with a significantly decreased acidification of the mucosa during shock (intramural pH 7.24 +/- 0.02 vs 6.97 +/- 0.02) and significantly increased oxygen saturation of the gastric mucosa (30 +/- 6 vs 5 +/- 2). These data indicate that topical oxygenated perfluorochemicals protect the gastric mucosa against mucosal damage provoked by hemorrhagic shock, and this protection seems to be mediated by an increased oxygen saturation of the gastric mucosa. Tonometry and reflectance spectrophotometry thus are able to predict the critical level of gastric mucosal ischemia.

Enteral nutrition as a risk factor for nosocomial pneumonia

Nutritional support of critically ill patients in the intensive care unit is important, since adverse effects of malnutrition are multiple and common. Nutrition via the enteral or gastrointestinal tract is often preferred over central venous or total parenteral nutrition as the initial choice of nutritional therapy due to its relative ease of administration, lower cost and infrequent association with severe complications. Recent data suggest that nosocomial pneumonia, a severe and ominous complication of critical illness, is related to gastric colonization secondary to alkalinization of stomach contents by antacids and H2-antagonists. Nosocomial pneumonia may also be related to enteral nutrition. Gastric microbial growth increases after the onset of enteral nutrition. Gastric organisms can be transmitted to the trachea and result in tracheal colonization and nosocomial pneumonia. Gastric to tracheal transmission of organisms is probably related to pulmonary aspiration. Several factors are important in pulmonary aspiration, including nasogastric tube size, method of nutrient delivery, patient position, and gastric and intestinal motility. Enteral nutrition must be considered in both the evaluation of mechanisms of nosocomial pneumonia and the strategies of prophylaxis.