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.

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.

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 (meq/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.

How are the ratios maintained?
The organs that maintain control of the electrolytes are:

1. The lungs. The lungs remove carbon dioxide, which is the basis of bicarbonate.  They can remove greater or lesser amounts of bicarbonate depending on what is happening in the body fluids.  Their primary function as regards electrolytes, is to provide for the control of acid balance in the body.
2. The Kidneys. The kidneys control the amounts of sodium and potassium excreted by the body.  Almost all the sodium can be saved, but there is an irreducible amount of potassium that is lost, even when the body is potassium depleted.  The kidneys also can save nearly all the water except that which is lost in the lungs and skin, and in the feces. The kidney can deal with overloads of sodium and potassium by secreting these elements into the urine.  *Normal kidneys can take care of about 1 meq potassium per kilogram of body weight per hour. This would be equal to an IV infusion rate of 7.5 to 10 meq/hour for a 15 lb. Lhasa - a rate almost impossible to acheive. The usual maximum rate would be more like 4 meq/hr assuming a very high 200cc /hour of a 20meq/liter solution. Normal infusion rates for a 15 lb. dog would be more in the neighborhood of 20 - 50 cc/hour, or 0.4 to 1 meq/hour of potassium.

Dehydration and its treatment
If you look at what may be lost in vomit and diarrhea, it is obvious that all the important salts can be lost at an astonishing rate.  In Parvovirus infection, plasma and blood are also being lost.  Obviously, unless these fluids and salts are replaced, the animal will die.  The small bowel lining is destroyed by the parvovirus, so that nothing will be absorbed by mouth, not to mention that the vomiting and diarrhea also make the oral route impossible.  Treatment is based on:

1. Replacement of water. This is estimated on the basis of the amount being lost, plus the daily requirement.  Losses may be much greater than estimated, since very large amounts of fluid can be sequestered in the bowel, and in swelling of the bowel wall.  In this regard it is very useful to immediately weigh any animal which had begun to have vomiting or diarrhea, before it has dehydrated, so that you have a baseline from which to estimate losses.
2. Replacement of salt. The initial fluid used should contain about the same salt composition as blood plasma, because that is approximately what is being lost.  Later, more potassium, and magnesium may need to be added to compensate for the disproportionate losses.  One reason for this is that hydrochloric acid is lost from the stomach with vomiting.  In order to maintain acid-base balance in the body, for each atom of hydrogen lost from the stomach, the kidney is obliged to give up a potassium atom to the urine.
3. Maintaining an energy source. In order to keep the vital organs functioning, the blood sugar has to be maintained. Solutions containing 5% glucose, while not meeting the caloric needs of the animal, can support the energy requirements of vital organs.
4. Prevention of secondary infection. The small bowel has been stripped of its lining by the parvovirus. This leaves it wide open to invasion by bacterial pathogens. Antibiotics which cover gram negative bacteria are normally used. If broad spectrum antibiotics are used for more than a week, a superinfection of a bacterium, Clostridium Difficile, can occur, which can also cause a severe diarrhea. This can be prevented by using oral Metronidazole 2.5 - 5 mg/kg three times a day.
5. Nursing care. Nothing is more important than warmth, comfort, skin care, and the presence of a trusted human caretaker. Animals can easily give up the will to live if deprived of social interaction and comfort. I would urge anyone who has a desperately ill animal to do home care, with the cooperation of your vet, unless there is a facility available which offers intensive care. No-one can give your dog what you can, even if that is only a happy death. Anyone can learn how to manage IVs at home, and how to put IV medications in the tubing.

1. Urine volume. Most young dogs with parvovirus have good kidneys.  When the blood volume has been replenished with fluid, a normal amount of urine will be produced. You've gone too far if the quantity is much greater than normal.  Normal urine output for a healthy, well hydrated 15 lb. dog would be 100 to 200 cc in 24 hours.
2. Pulse. Dogs the size of a Lhasa normally have a pulse of 90 - 120 per minute.  Dogs with parvovirus are anemic, so their pulses will be higher than normal, but you know fluid replacement is heading in the right direction when the pulse is approaching normal.
3. Respirations. You can easily take the respiratory rate of one of your other dogs of the same age (at rest) to get an idea of the normal rate.  If the rate is very rapid, this is an ominous signal of air hunger.  The animal may need transfusion.  The vet can do this, particularly if you have a healthy, related donor.