WHAT IS BLOAT?
Canine bloat occurs when there is gas production in the stomach and that gas buildup is unable to be expelled via belching or vomiting, or passed through the intestines and out of the dog as flatulence.  Some bloat cases occur very rapidly when fermentation of grains in the wet and warm stomach environment create gas.  The influence of grain in creating an environment conducive to bloat seems even more plausible in that it is very rare for dogs that consume meat-based diets to develop bloat.  Generally, bloat is the extreme dilation of the stomach as a result of gas buildup that cannot escape the stomach.

WHAT TYPES OF BLOAT ARE THERE?
GASTRIC DILATATION... is simply the expansion of the stomach due to the buildup of gas or material in the stomach.
GASTRIC VOLVULUS (TORSION)... is the condition where the stomach rotates (flips on its long axis) and thereby twists the esophagus and small intestine closed so there is no passage of stomach contents or gas in or out of the stomach.
 

HOW DOES BLOAT HAPPEN?  
Scientists have tried to decades to learn about how bloat occurs by setting up bloating conditions in the laboratory with laboratory dogs... and consistently have failed in producing the spontaneous bloating that occurs with canine house pets.  The usual history is of a dog of a large breed that has recently eaten a meal of dry dog food and then exercises or engages in some physical  activity.  On occasion, though, there is no history of physical activity and the dogs is suddenly seen trying to retch and vomit unsuccessfully.  The dog paces, becomes uncomfortable, attempts to pass stool and repeatedly makes retching, gagging noises.  Salivation is common.  At this stage it is impossible to determine what type of bloat is occurring.   In the photos above, the fortunate Malamute had a simple Gastric Dilatation with no torsion or volvulus.  Once the stomach contents and gas were eliminated via a plastic stomach tube, and the stomach was flushed and antibiotics administered to prevent further bacterial fermentation and gas production, the surgery was over and the dog recovered rapidly and successfully.  With Torsion or Volvulus present, far greater damage occurs to internal blood vessels and stomach tissues, plus the spleen gets caught up in the twisted mess of tissues and becomes starved for oxygen along with the stomach.  Eventually the heart is affected due to the major interruptions in blood flow and heart rhythms;  plus the pressure on the heart and diaphragm prevents normal cardio-pulmonary function. When the blood supply in the abdomen’s major arteries is compromised, blood flow to the heart and the cardiac output decrease, leading to low blood pressure, and eventually, shock. 

The production of gas in the stomach sometimes overwhelms the dog's ability to belch it away or pass it through the bowel as flatulence.  There are various theories about the gastric chemistry that occurs to produce this sudden buildup of gas.  Plus, many dogs that become uncomfortable as the gas builds up will begin to swallow air, compounding their dangerous condition.

HOW IS BLOAT TREATED?
Treatment needs to be undertaken immediately.  Time is a very decisive factor in the success or failure of correcting bloat.  Once presented to a veterinarian, a dog with bloat will become the center of attention and all other activities at the animal hospital assume a lesser priority.  Supportive medications such as cortisone, antibiotics and intravenous fluids are started immediately.  The veterinarian may need to decompress the stomach initially (before surgery) by inserting a large diameter needle into the stomach right through the abdominal wall.  An audible hiss is heard as the gas passes through the needle.  Once this is performed the doctor administers intravenous anesthetic in very small amounts because the patient in this state of affairs requires very little intravenous anesthetic to facilitate the passing of the endotracheal tube through which the gas anesthetic is administered.  Some veterinarians skip the intravenous anesthetic and, via a face mask, administer gas anesthesia such as Isoflurane... once the patient is unconscious the endotracheal tube is passed into the trachea to allow continuous control of anesthesia.

Once anesthesia is at the proper level, a stomach tube (see the photo above) is gently inserted down the esophagus in an attempt to gain entry into the stomach.  If there is a Volvulus present and the twisting of the esophagus/stomach junction prevents passing the stomach tube into the stomach, the doctor will need to incise the stomach to dissipate the gas and bring the stomach back to a reasonable state of size and pressure.  If no volvulus (twisting or rotation of the stomach on its axis) is present such as in the case presented here, with careful and gentle manipulation by the surgeon within the abdominal cavity the stomach tube can be directed into the stomach and the gas and stomach contents can be drained by gravity out of the dog.

Once the intra-gastric pressure is lowered the presence or absence of rotation of the stomach can be ascertained.  Also, if a volvulus is present, the spleen is also involved and often its blood supply becomes strangulated.  Occasionally, the doctor will elect to remove the spleen at this time.  The health of the stomach is established... in cases where the gastric dilatation has been present for hours and the pressure is very high, the stomach wall will be very thin and stretched and there may be areas of necrosis (cell death).  In the photos above a well vascularized stomach wall is evident... that a god situation.  In severe bloat where the stomach is stretched for long periods, the blood supply is shut down and the stomach wall appears bluish or blackened.  This blackish coloration suggest permanent cell death and damage.  Any time there is necrosis of the stomach wall the prognosis for a successful resolution of the case is very poor.  The massive cell death and absorption of toxins through the stretched stomach wall creates severe cardiovascular damage and blood pressure problems.  Once a state of shock begins, the chances of recovery for the patient are slight.  Even dogs that survive surgery and seem to be recovering often succumb to endotoxic shock hours and even days after the procedure.

When the stomach contents are emptied through the stomach incision, the stomach wall is finally sutured closed.  If a volvulus is present the surgeon will rotate the stomach (and spleen) back into the normal anatomical position.  Then the stomach tube is inserted through the mouth into the stomach and additional flushing and antibiotic administration is done.  Before closing the abdominal incision the surgeon usually will tack (affix with sutures) the stomach wall against the inner abdominal wall (actually just inside the rib area) to prevent future episodes of gastric dilatation/volvulus.  This tacking procedure is excellent insurance against a volvulus happening again.

WHAT CAN BE DONE TO PREVENT BLOAT?
The best suggestions are to feed the dog two small meals a day instead of one large meal.  Do not allow the dog to drink large quantities of water at one time... have water available at all times.  Do not allow exercise or other vigorous activity for at least two hours after a full meal.  Feed a diet composed of more meats and less grain.

BREEDS AT MOST RISK

Below are photos of a dog that had repeat episodes of gastric dilatation.  Luckily, under anesthesia, a stomach tube was able to be passed and the gas and pressure was relieved.  The stomach was flushed, appropriate medication was given to help prevent cardiovascular shock, infection and to eliminate gas forming bacteria in the stomach.

Arrows point to the distended abdomen.  This dog is normally very thin.	This view is of the dog laying on its side under anesthesia.  The ballooning of the abdomen is apparent.	This is the x-ray image of the dog prior to the procedure to relieve the gas distension.