Gastric dilatation-volvulus (GDV) is an emergency condition involving abnormal, extensive gas distention and rotation of the stomach. Although the stomach is initially the primary organ involved in GDV, many other organs are quickly compromised if this condition is left untreated.
The stomach normally rests in the left cranial abdomen. It is divided into four regions: cardiac, fundic, body and pyloric. The cardiac region is the area in closest proximity to the oesophagus and is one of the most cranial aspects of the stomach. The fundic region is also cranial and provides a temporary holding area for food coming into the stomach via the oesophagus. The body of the stomach is the middle region and is contained within the lesser and greater curvatures. The pyloric region is the most caudal aspect of the stomach and empties into the duodenum.
When gastric dilatation and volvulus occur, the stomach fills with gas and twists on its axis. The pylorus moves from the right cranial abdomen, ventrally, around the fundus of the stomach and rests in the left abdomen, beside the oesophagus. The rotation of the stomach obstructs the oesophagus and the pylorus. The obstructed entrance and exit to the stomach prevent gastric emptying. Belching and vomiting are no longer possible. Passage of food and gas into the digestive system is also no longer possible. Thus, the stomach cannot purge its contents; it can only expand to accommodate them. Continued gas production (from carbohydrate metabolism) and the production of normal gastric juices further contribute to the volume trapped in the stomach. The digestive juices that are trapped in the stomach are rich in hydrogen (H+ ions). Since these particles are prevented from entering the vasculature, metabolic alkalosis may be evident on blood gas analysis. Pooling of fluids in the stomach translates to bloodwork that indicates haemoconcentration. Patients often have an increased packed cell volume on presentation.
As the stomach stretches under pressure from the excess gas, it compresses the major vessels in the abdominal cavity. The vena cava and portal vein are primarily affected. Compression of the vena cava reduces venous blood return to the heart. Compression of the portal vein traps circulating blood in the gastrointestinal tract, further decreasing the blood volume available to return to the heart. Decreased venous blood return leads to decreased cardiac output and hypotension. Ultimately, perfusion is compromised and further organ damage is likely without prompt intervention.
Vascular congestion and poor perfusion lead to hypoxia and tissue ischaemia. Since lactic acid is a product of anaerobic metabolism, lactate levels rise and exceed the rate at which lactic acid can be cleared by the liver and kidneys. Measurement of lactate levels can be helpful as a prognostic indicator since lactate level can indicate how severely the patient’s circulation has been affected. Studies have shown that lactate concentrations > 6.0 mmol/l indicate a poor chance of survival, whereas a concentration < 6.0 mmol/l suggest a good chance of survival.
The dilated stomach exerts force on the diaphragm, encroaching on the thoracic space; creating a decreased tidal volume and increased respiratory rate. Respiratory acidosis is often present, but can be veiled by the mixed acid-base disorder created by other aspects of GDV (metabolic acidosis created by increased lactate vs. metabolic alkalosis created by sequestration of H+ ions in the gastric lumen).
Perfusion to the stomach is compromised during torsion. The abnormal position of the stomach interrupts the delivery of oxygenated blood to gastric tissue. As a result, sections of the gastric wall become hypoxic and start to die. At surgery, these sections of the stomach often appear darkened and bruised, taking on a greyish-green to purple or black coloration. Devitalised sections must be carefully evaluated and possibly resected during corrective surgery; an event that potentiates further complications.
The spleen may also be involved in the volvulus. As the stomach rotates, it pulls the spleen up and to the right. The spleen becomes partially obstructed, undergoing venous congestion. Splenomegaly ensues. Depending on the degree and potentially the duration of rotation, the splenic vessels may rupture and haemorrhage into the abdominal cavity which can cause hypovolaemia. Haemorrhage may be indicated if initial bloodwork reveals a decreased packed cell volume. If the spleen does not return to its normal size once the torsion has been corrected, if there are obvious infarcts, or if avulsed vessels are noted, the spleen is typically resected.