bloat, excessive accumulation of gases in the rumen, the first stomach of a cud-chewing animal. Bloat is probably formed to a large extent by bacterial action. It occurs in all ruminants, but is most common in cattle; it appears typically in animals that graze on newly developed, highly productive, lush green pastures, especially during a wet summer on clover-dominant pastures. Bloat can result from excess frothiness of the ruminal ingesta or loss of tone and motility of the rumen. Both of these conditions will prevent the normal eructation process. Treatment consists of passing a tube to the stomach or of reducing the foam formation by oral administration of mineral or vegetable oils. Prevention is attempted by carefully controlled management practices, administration of antibiotics, and the use of nontoxic oils.

Bloat is a medical condition in which the stomach becomes overstretched by excessive gas content. It is also commonly referred to as torsion, gastric torsion, and gastric dilatation-volvulus (GDV) when the stomach is also twisted. The word bloat is often used as a general term to cover gas distension of the stomach with or without twisting. The name comes from the Middle English blout, meaning soft or puffed, which is from the Old Norse blautr, meaning soft or soaked. Meteorism, its name derived from the writings of Hippocrates, is now rarely used in English. The condition occurs most commonly in domesticated animals, especially ruminants and certain dog breeds.

In dogs, gas accumulation in the stomach may cause or be caused by a volvulus, or twisting, of the stomach, which prevents gas from escaping. Deep-chested breeds are especially at risk. Mortality rates in dogs range from 10 to 60 percent, even with treatment. With surgery, the mortality rate is 15 to 33 percent.

Causes

Bloat in dogs is likely caused by a multitude of factors, but in all cases the immediate prerequisite is a dysfunction of the sphincter between the esophagus and stomach and an obstruction of outflow through the pylorus. Some of the more widely acknowledged factors for developing bloat include increased age, breed, having a deep and narrow chest, stress, eating foods such as kibble that expand in the stomach, overfeeding, and other causes of gastrointestinal disease and distress. Studies have indicated that the risk of bloat in dogs perceived as happy by their owners is decreased, and increased in dogs perceived as fearful. This may be due to the physiological effects of the dog's personality on the function and motility of the gastrointestinal system. Dogs with inflammatory bowel disease may be at an increased risk for bloat.

Dietary factors

One common recommendation in the past has been to raise the food bowl of the dog when it eats. However, studies have shown that this may actually increase the risk of bloat. Eating only once daily and eating food consisting of particles less than 30 mm in size also may increase the risk of bloat. One study looking at the ingredients of dry dog food found that while neither increased grains, soy, or animal proteins increased risk of bloat, foods containing an increased amount of added oils or fats do increase the risk, possibly due to delayed emptying of the stomach.

Breed susceptibility

The five breeds at greatest risk are Great Danes, Weimaraners, St. Bernards, Gordon Setters, and Irish Setters. In fact, the lifetime risk for a Great Dane to develop bloat has been estimated to be close to 37 percent. Standard Poodles are also at risk for this health problem, as are Doberman Pinschers and Rottweilers. Basset Hounds have the greatest risk for dogs less than 23 kg.

Pathology

The stomach twists around the longitudinal axis of the digestive tract, also known as volvulus. Gas distension may occur prior to or after the stomach twists. The most common direction for rotation is clockwise, viewing the animal from behind. The stomach can rotate up to 360° in this direction and 90° counterclockwise. If the volvulus is greater than 180°, the esophagus is closed off, thereby preventing the animal from relieving the condition by belching or vomiting. The results of this distortion of normal anatomy and gas distension include hypotension (low blood pressure), decreased return of blood to the heart, ischemia (loss of blood supply) of the stomach, and shock. Pressure on the portal vein decreases blood flow to liver and decreases the ability of that organ to remove toxins and absorbed bacteria from the blood. At the other end of the stomach, the spleen may be damaged if the twisting interrupts its blood supply. If not quickly treated, bloat can lead to blood poisoning, peritonitis and death by toxic shock.

Symptoms

Symptoms are not necessarily distinguishable from other kinds of distress. A dog might stand uncomfortably and seem to be in extreme discomfort for no apparent reason. Other possible symptoms include firm distension of the abdomen, weakness, depression, difficulty breathing, hypersalivation, and retching without vomiting. A high rate of dogs with bloat have cardiac arrhythmias (40 percent in one study). Chronic bloat may occur in dogs, symptoms of which include loss of appetite, vomiting and weight loss.

Diagnosis

A diagnosis of bloat is made by several factors. The breed and history will often give a significant suspicion of bloat, and the physical exam will often reveal the telltale sign of a distended abdomen with abdominal tympany. Shock is diagnosed by the presence of pale mucous membranes with poor capillary refill, increased heart rate, and poor pulse quality. X-rays (usually taken after decompression of the stomach if the dog is unstable) will show a stomach distended with gas. The pylorus, which normally is ventral and to the right of the body of the stomach, will be cranial to the body of the stomach and left of the midline, often separated on the x-ray by soft tissue and giving the appearance of a separate gas filled pocket (double bubble sign).

Treatment

Bloat is an emergency medical condition: having the animal examined by a veterinarian is imperative. Bloat can become fatal within a matter of minutes.

First Aid

A dog owner can sometimes relieve the immediate pressure of bloat by passing a tube down the throat, as an emergency first aid technique. This is not an easy task and cannot readily be improvised; some web sites document so-called bloat first aid kits and contain descriptions of the first aid a dog owner can provide at the time an attack of bloat is discovered. This is not a substitute for immediate veterinary treatment. There is risk of esophagus or stomach rupture if the tube is inserted too forcefully, or if the stomach is necrotic.

Veterinary treatment

Treatment usually involves resuscitation with intravenous fluid therapy, usually a combination of isotonic fluids and hypertonic saline or a colloidal solution such as hetastarch, and emergency surgery. The stomach is initially decompressed by passing a stomach tube, or if that is not possible, multiple trocars can be passed through the skin into the stomach to remove the gas. During surgery, the stomach is placed back into its correct position, the abdomen is examined for any devitalized tissue (especially the stomach and spleen). A partial gastrectomy may be necessary if there is any necrosis of the stomach wall.

Prevention and reduction of recurrence

Recurrence of bloat attacks can be a problem, occurring in up to 80 percent of dogs treated medically only (without surgery). To prevent recurrence, at the same time the bloat is treated surgically, a right-side gastropexy is often performed, which by a variety of methods firmly attaches the stomach wall to the body wall, to prevent it from twisting inside the abdominal cavity in future. While dogs that have had gastropexies still may develop gas distension of the stomach, there is a significant reduction in recurrence of gastric volvulus. One study showed that out of 136 dogs that had surgery for bloat, 4.3 percent of those that did have gastropexies had a recurrence, while 54.5 percent of those without the additional surgery recurred. Gastropexies are also performed prophylactically in dogs considered to be at high risk of bloat, including dogs with previous episodes of bloat or with gastrointestinal disease predisposing to bloat, and dogs with a first order relative (parent or sibling) with a history of bloat.

Precautions that are likely to help prevent bloat include feeding small meals throughout the day instead of one big meal and not exercising immediately before or after a meal.

Prognosis

Immediate treatment is the most important factor in a favorable prognosis. A delay in treatment greater than six hours or the presence of peritonitis, sepsis, hypotension, or disseminated intravascular coagulation are negative prognostic factors.

Bloat in cattle

In cattle, bloating is most often caused by the animal eating damp, green alfalfa. New (green) alfalfa hay, especially that made from the first cutting of the year, must be kept from cattle until it has aged for several weeks. When a calf has become bloated, often a section of hose is inserted down the throat and into the stomach to relieve the gas pressure that builds up. A veterinarian should be called for treatment. As with dogs, death of the animal often results if bloat is not quickly treated.

References

External links

• Bloat The Mother of All Emergencies from The Pet Health Library
• Dog Owner's Guide: Bloat
• Whitepaper on Healthy Dog Eating