Parvovirus is a killer of young dogs. Proper replacement of fluid and electrolytes is life saving. Understanding a few simple principles of fluid and electrolyte balance may enable you to save your dogs with Parvovirus, and to care for them at home.

Parvovirus
Canine parvovirus is a highly contagious viral infection causing lethargy, loss of appetite, vomiting and diarrhea. It occurs more commonly in young dogs than in adults, but can be severe and fatal in dogs of all ages. Infection occurs by ingestion of the virus. Shortly after ingestion, the virus replicates in the lymphoid tissue of the mouth and then rapidly spreads throughout the body via the blood stream and can be found in tissues throughout the body especially the intestines, bone marrow, and in the young dog, heart. The virus thrives on rapidly dividing cells, and this is the reason it localizes in the intestines and bone marrow. In the young, growing puppy, the cells of the heart are also rapidly dividing and are also therefore targets for the virus. Infection of the bone marrow results in a drop in both white and red blood cell counts. About 4 days after exposure, the typical signs of lethargy, vomiting and diarrhea begin. The small bowel is principally affected, and the profuse vomiting and bloody diarrhea can result in severe anemia, as well as severe dehydration and shock.

Shock
Shock is a condition of inadequate blood supply (perfusion) of the body tissues. It can have several causes:

1.Cardiogenic: This type of shock is seen when the heart muscle is unable to pump adequate amounts of blood due to failure of the heart muscle itself. (Otherwise known as "pump failure") This may occur in young puppies with parvo, when the virus attacks the heart muscle. There is no treatment for this, and these pups usually succumb.

2.Hypovolemic: This is due to inadequate blood volume. This is the common shock encountered in the severe dehydration resulting from parvovirus infection. The symptoms are paleness of peripheral tissues (i.e. Gums), rapid pulse (the heart has to beat faster to compensate for the diminished volume) and decreased urine output (the kidneys are poorly perfused and they are in any case saving water).

3.Toxic: Bacterial toxins can poison the vessel walls, making them unable to contract down. Even with a normal blood volume, blood will pool in the veins, and not be returned to the heart in adequate amounts to maintain normal circulation. This can be a late manifestation in parvovirus. Prevention of bacterial infection by using broad spectrum antibiotics is important.

Body Water
The body of an adult dog is approximately 60% water. Of that water, 60% is contained within the cells, and 40% is contained outside the cells, in the blood and lymph. This means that in a 7.5 kilo (15 lb.) adult, there is 4.5 kilos of water (4.5 liters or 4.7 qt.) 2.7 liters of that water is inside the cells, and 1.8 liters is in the blood and lymph. The portion of the body water inside the cells is called the ICF or intracellular fluid. The part outside the cells is the ECF or extracellular fluid.

Puppies
Puppies have a greater percentage of water in their bodies. Newborns are 75% to 80% water. By 4 months of age the percentage is 65%. The distribution of ECF and ICF is about the same as in the adult.

Dehydration and Body Water
When an animal loses body water through diarrhea or vomiting, that water is lost from the ECF. The body compensates for this loss in several ways:

1.The peripheral blood vessels constrict, moving most of the blood toward the vital organs.

2.The kidneys begin reabsorbing more water and salts, - saving water.

3.Water begins moving out of the cells - moving across the cell membranes from the ICF to the ECF.

Electrolytes
Electrolytes are salts contained in blood and cellular fluids. The difference between the concentration of these salts inside and outside the cells causes an electrical potential very similar to that of an electric battery. This battery-like potential is what causes the contraction of muscle cells and the transmission of impulses in nerve cells. Brain function, respiration and heart pumping are directly dependent on the maintenance of these electrical potentials.

The primary electrolytes are Sodium and Potassium. Sodium and potassium are present linked to Chloride, (sodium chloride, - common table salt), or to Bicarbonate, (sodium bicarbonate - common baking soda). Other elements vital to cell membrane stability are Magnesium and Calcium. We refer to the concentrations of these electrolytes in terms of "Millequivalents per liter", or meq, which is a measure of how many active units (ions) of the substance are present in a one liter of fluid.

Sodium
Sodium is the major component of the ECF. It is actively pumped out of the cells and this "sodium pump" in the cell membrane is what maintains the electrical potential of the cell. If cells are injured or poisoned, and the sodium pump fails, the cell dies. The daily requirement for sodium in a 15 lb. dog is about 6.5 meq.

Potassium
Potassium is the major component of the ICF. It is responsible, along with sodium, for maintaining the cell potential. If the Potassium outside the cell varies from normal by more than 3 meq up or down, the heart may stop. In administering IV potassium, the rate of infusion must be carefully monitored. Rapid infusion can kill. Potassium should not be given without constant laboratory monitoring if the kidney function is impaired. The concentration of potassium in IV fluids should not exceed 20 - 25 meq/Liter. The daily requirement for Potassium in a 15 lb. dog is 5.5 meq.

Electrolytes in body fluids

Electrolyte( meg/L)	ECF	ICF	Diarrhea	Vomit
Sodium	140	10	120	60
Potassium	5	150	10 - 55	10
Chloride	105		120	90
Bicarbonate	25	10	25
Magnesium	2	40

From this table you can see how different the electrolyte composition is inside and outside the cells, and the quantities of these ions that can be lost with vomiting and diarrhea. Remember that unless the ratios of intracellular and extracellular components can be maintained, all electrical activity will stop, -heart, brain, breathing.

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