Vet360, December 2016 - Page 27

CPD ACCREDITED ARTICLE • • • • Gastric factors: An increased gastrin concentration, decreased stomach motility, and delayed gastric emptying have been mentioned as risk factors but have never been demonstrated.5-8 Dietary habits: Diet, large amounts fed at each feeding, the frequency of feedings (one meal a day), a fast eating style, and exercise or stress after a meal are contributing factors for the development of GDV.5-8 Signalment and physical attributes: Large-breed dogs, dogs with a large thoracic depth-to-width ratio, underweight dogs, and older animals are at higher risk to develop GDV. Dogs with a happy personality might be at less risk.6-9 Splenectomy: The removal of a large spleen has been associated with the development of GDV in some case reports; however, studies have not proven splenectomy to be a risk factor for the development of GDV in dogs. GDV Progression The stomach moves in a clockwise rotation. Displacement of the pylorus occurs from the right side toward the ventral midline. It passes over the fundus and body to the left abdominal wall close to the lower esophageal sphincter. At the same time, the fundus goes in a ventral direction toward the right abdominal wall. The pyloric antrum ends up in a dorsal position on the left side. Because of the attachment of the omentum to the greater curvature of the stomach, the omentum covers the stomach after volvulus. The displacement of the spleen may be related to the degree of volvulus. The spleen is usually engorged or can undergo torsion on its own pedicle. Thrombosis of the splenic artery can also occur. Usually, 180 degrees of stomach rotation is seen, but 360-degree rotation is possible. Counterclockwise rotation is not really possible, or it is limited to 90 degrees since the pylorus cannot move dorsally in the abdominal cavity. Gastric dilatation causes compression of the caudal vena cava and portal vein.10-13 Sequestration of blood in the spleen, kidneys, and gastrointestinal tract occurs. Compression of the caudal vena cava and portal vein induces a decreased venous return, resulting in hypovolaemic shock. Hypotension and venous stasis result in cellular hypoxia and anaerobic metabolism. Elevated portal pressure compromises microcirculation in the viscera and reduces oxygen delivery to the gastrointestinal tract. The pancreas in the presence of ischaemia produces myocardial depressant factor (MDF).12 Ischaemia, acidosis, liberation of the MDF by the pancreas, and the production of free oxygen radicals induce myocardial ischaemia and reduce cardiac contractility.12-14 Subendocardial ischaemia and necrosis combined with tachycardia and acid-base imbalance induce arrhythmias. Vascular stasis, hypoxia, and acidosis can induce disseminated intravascular coagulopathy (DIC). Mechanical limitation of diaphragmatic movement by a dilated stomach and decreased pulmonary compliance results in respiratory dysfunction. Tissue hypoxia results from decreased cardiac output and respiratory impairment. Increased gastric intraluminal pressure, portal hypertension, and venous stasis with thrombosis cause gastric mucosa stasis, hypoxia, and oedema. Gastric wall necrosis can then develop in the fundus along the greater curvature. Because of distention of the stomach, vascular wall disruption causes mucosal hemorrhage. Avulsion of branches from the short gastric arteries during rotation of the stomach contributes to blood loss, hypovolemia, and restriction of blood flow to the stomach. Clinical Signs Dogs with GDV are usually presented for evaluation of unproductive vomiting, retching, hypersalivation, and a distended abdomen. They have progressively distending and tympanic cranial abdomens, and they may be restless. As the severity of the distention increases, the dog can become weak, laterally recumbent, and tachypneic. Dogs with GDV often present with weak peripheral pulses, pale mucous membranes, prolonged capillary refill times, tachycardia, and tachypnoea. Abdominal pain is rarely present on palpation. Dogs with mesenteric volvulus also present with severe abdominal distention. Usually, these dogs are in a lot of pain and deteriorate rapidly in severe septic shock. Persistence of the clinical signs of GDV for more than five hours has been associated with a poor prognosis.15 The severity of the clinical signs on presentation has been found to be an indicator of patient survival.16 In general, dogs that are bright and alert when presented have better prognoses than do dogs that are laterally recumbent. It has been shown that recumbent patients have 4.4 times greater probability of dying than do dogs that are ambulatory. If a patient is comatose, it has 36 times greater probability of dying. Dogs that appear depressed on presentation have a three times greater probabilit 䁽)她)ͥ)X́ѕ͕͕ѥН́ѽ䰁ͥаͥᅵѥɕձ̸IɅ)مՅѥ́ɕեɕѼɴѡ̸ͥ)M)X́Ё͕ɝеɕ)̸%Ёͼ͕͵̸́)ɽѡ́ѼЁ啅́ٔѕ9)͕ɕѥ́ٔɅѕ)Aͥᅵѥɕձ)=ͥᅵѥЁ́ͥѼɝѕ=ɍͥͽչ)ɽՍѥ䁉չх()%Ք؁ 5 H؁((