The Layman's Guide to Fluid Replacement
by Catherine Marley, MD
(http://www.lhasa-apso.org)
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 (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.
Daily intake requirements for a healthy 15
lb. dog:
Calories = 250 - 500
Water = 300 cc
Protein = 3.2 grams
Sodium = 6.5 meq
Potassium = 5.5 meq
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
super infection of a bacterium, Clostridium Difficile, can occur, which can
also cause a severe diarrhea. This can be prevented by using oral Metronidazole
(Flagyl) 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.
How do you know it's working?
At home you do not have the luxury of a laboratory to measure the
electrolytes. Fortunately, that is not necessary. Monitoring progress depends
on three easily observable signs:
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
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.
Armed with this bit of knowledge, you can be in a position to evaluate the care
your Veterinary Hospital may or may not be capable of giving, and of applying a
common sense rationale to caring for your dog (if your vet will co-operate) at
home.