INTRODUCTION

Gastrointestinal (GI) hemorrhage is an important cause of blood loss anemia and a potentially life-threatening condition in dogs.¹ It is reported less frequently in cats. It may be acute or chronic, occult (no visible blood) or overt (grossly visible blood), and can vary from mild, self-limiting states to severe life-threatening conditions. Significant GI hemorrhage can often be detected during history and physical examination. However, on occasion even acute severe GI hemorrhage may be overlooked if signs localizing blood loss to the GI tract are not present or if concurrent disease obscures the diagnosis.^2,3 In addition, because even mild cases may progress to life-threatening events, it is important to rapidly identify patients with GI hemorrhage and institute therapies to prevent their deterioration.

ETIOLOGY

GI hemorrhage in dogs and cats can be the result of a primary insult to the GI tract or may be secondary to a systemic disease process. It may originate in the esophagus, stomach, small intestine, or large intestine. As such, a number of pathologic processes have been associated with GI hemorrhage. In general, these can be divided into three broad categories: diseases causing ulcers, diseases causing coagulopathies, and diseases associated with vascular anomalies. Animals may have single or multiple predisposing causes.^1,4

The most commonly reported cause of GI hemorrhage in dogs and cats is GI ulceration.^3-6 The severity of GI hemorrhage associated with ulcers varies with the degree and extent of mucosal erosion. With erosion into an underlying artery, the magnitude of bleeding is related to the size of the arterial defect and the diameter of the artery.⁷ Diseases associated with GI ulceration in dogs and cats are listed in Box 130-1. Nonsteroidal antiinflammatory drugs (NSAIDs) and hepatic disease are the most commonly reported risk factors for ulcers in dogs (Color Plate 130-1).⁴ Neoplasia is a common risk factor for ulcers in cats, with systemic mastocytosis, gastrinoma, intestinal lymphosarcoma, and adenocarcinoma being the most commonly reported tumors.³ Inflammatory bowel disease may also be an important nonneoplastic cause of GI ulceration in cats and dogs.³ Stress ulcers are a frequent cause of GI hemorrhage in critically ill human patients and have been reported in dogs and cats following hypovolemia and surgery.^3,8 The true incidence and significance of stress ulcers in critically ill cats and dogs has not been determined, but should be considered in patients that develop GI hemorrhage while in the hospital.

Coagulation disorders associated with GI hemorrhage include rodenticide toxicity, disseminated intravascular coagulation, coagulation factor deficiencies (factor XII and prekallikrein deficiency), and thrombocytopenia.^1,5 Thrombocytopenia is the most common coagulation disorder resulting in GI hemorrhage in dogs and should not be overlooked.¹ Coagulation disorders resulting in GI hemorrhage appear to be less common in cats.

Vascular anomalies, because of the high incidence of varices, are a common cause of GI hemorrhage in humans. In contrast, only a few cases of vascular anomaly have been reported in the veterinary literature and it appears to be an infrequent cause of GI hemorrhage in dogs and cats.⁹ It should be considered when more common causes of GI hemorrhage have been ruled out.

HISTORY AND PHYSICAL EXAMINATION

With extensive hemorrhage, vomiting, diarrhea, or ulcer perforation, patients with GI hemorrhage may present in a state of shock due to blood loss, hypovolemia, endotoxemia, or sepsis. Examination findings consistent with shock include tachycardia, diminished or thready arterial pulses (particularly peripheral), cool extremities, prolonged capillary refill time, and pale mucous membranes. Aggressive resuscitative therapies to reverse the state of shock take precedence (see Chapters 10 and 65, Shock and Shock Fluids and Fluid Challenge, respectively), and localization of the site of hemorrhage and tailored therapies may need to be delayed until the cardiovascular system is stable.

Once resuscitative efforts have commenced, a complete history and physical examination should be performed. Hematemesis (vomitus with the appearance of coffee grounds or frank blood), hematochezia (passage of bright red or frank blood with or without stool), or melena (black tarry stool) suggests the GI tract as a source of hemorrhage. However, these signs are not always evident clinically and may not appear until significant GI hemorrhage has occurred.^3,4,10 With duodenal hemorrhage, if reflux of duodenal contents into the stomach is insufficient, blood may not be visible in the vomitus.¹¹ However, when it is present, hematemesis suggests ongoing blood loss.¹² Diseases of the nasal cavity and oropharynx occasionally can cause hematemesis and melena from swallowing blood of epistaxis or hemoptysis (coughing of blood), and these causes should be considered. In addition, activated charcoal, bismuth (Pepto-Bismol), and diets high in iron can result in dark stools and should not be confused with melena.¹³

A history of aspirin or other NSAID administration is not uncommon.^4,10,14 There are case reports of GI ulceration, hemorrhage, and GI perforation occurring in veterinary patients that have received selective cyclooxygenase inhibitors at recommended therapeutic dosages.¹⁰ Decrease or loss of appetite with or without other signs of GI disease should prompt consideration of GI side effects in any patients receiving NSAIDs. The medication should be discontinued and the patient should be examined. In cases of thrombocytopenia or coagulation disorders, there may be a history of bleeding from other sites of the body including the nasal cavities or urinary tract. Thorough examination of the mucosal surfaces may reveal petechiae in severely thrombocytopenic patients. A search for subcutaneous nodules or masses may detect underlying mast cell tumors.

Because GI hemorrhage may be insidious in onset, especially when chronic, the abdomen should be examined care-fully. Abdominal palpation may localize areas of pain (tenderness, voluntary or involuntary guarding) or induce nausea, identify masses or foreign objects, or detect abdominal distention or a fluid wave. Splenomegaly or hepatomegaly may be identified in patients with mastocytosis, other neoplasia, or hepatic diseases. During initial evaluation or resuscitation of the patient, a careful rectal examination should be performed to detect frank blood or melena and to look for masses or foreign bodies.

Although hemorrhage from any site in the GI tract can be serious, upper GI hemorrhage tends to be more severe.^12,13 In addition, the etiology as well as the diagnostic tests and therapies for upper and lower GI hemorrhage may vary, making localization of the site of hemorrhage important.^5,13 Hematemesis or melena suggests upper GI hemorrhage.¹³ However, it is important to remember that it is the amount of time the blood remains in the GI tract and not necessarily the site of bleeding that determines its color.^13,14 Delayed GI transit time and retention of blood in the colon could result in melena associated with a lower GI tract lesion.^13,15 Hematochezia is usually reflective of large intestinal, rectal, or anal hemorrhage; however, severe acute intestinal hemorrhage can act as a cathartic, significantly decreasing GI transit time.^12-14 This may result in the passage of frank blood in the stool following significant blood loss into the upper GI tract.^12,14