Fluid therapy

What a stressful week.

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Fluid therapy in dogs

Fluid Therapy is the administration of fluids to a patient as a treatment or preventative measure. It can be administered via an intravenous, intraperitoneal, intraosseous, subcutaneous and oral routes. 60% of total bodyweight is accounted for by the total body water. This can further be divided into intracellular or extracellular as shown below.

Fluid therapy is indicated either when there is a loss of fluid to any part of these compartments or there is a risk of loss of fluid. The severity of the fluid loss, and the compartment from which it has been lost, influence the choice of fluid and the speed at which it needs to be administered. If fluid therapy is performed as a treatment then it is necessary to diagnose and treat the underlying condition.

Indications

Hypotension
Hypovolemia
Electrolyte, metabolic and acid base disorders
Decreased oxygen delivery
Geriatric patients at risk of organ failure

Degree of dehydration in animal

5% (below): No physical finding

5%: Dry oral mucous membrane but no panting or pathological bradycardia

7% : Mild moderate decreased skin turgor, dry oral mucous membranes, slight tachycardia,

10%:Moderate to marked degree of decreased skin turgor, dry oral mucous membrane, tachycardia, decrease pulse pressure

12%: Marked loss of skin turgor, dry oral mucous membrane and significant of shock

In mild dehydration, subcutaneous fluids are useful. Isotonic fluids should be used and no more than 5 to 10 ml/lb should be given at each injection site. The rate of subcutaneous fluid flow usually is governed by patient comfort. These fluids are aseptically administered and multiple sites are required to provide adequate fluid volume. Generally, all subcutaneous fluids are resorbed within 6 to 8 hours. If fluids are still noted subcutaneously after this time, the use of intravenous fluids to reestablish peripheral perfusion should be considered.

The intraperitoneal route is quick, easy, and the fluids will generally be reabsorbed thus increasing the circulating volume. However, there is the potential of bacterial peritonitis, perforating viscera, and decreasing ventilation from impeding diaphragmatic excursion. Experience with peritoneal dialysis in dogs has shown that peritoneal fluids often traverse the diaphragm, entering the thoracic space, and further affecting ventilation. Currently, intraperitoneal fluids cannot be recommended.

In general, intravenous fluid administration is indicated in dogs and cats with 7% or greater dehydration. There are numerous potential routes for intravenous fluid administration:

Peripheral veins
Jugular veins
Intraosseous

The amount of fluid needed for replacement depends on the patient's status. Of primary concern is the status of the blood volume and later concern is directed to restoration of total body water and electrolytes

3 phases of fluid therapy

Emergency phase
Replacement phase
Maintenance phase

Types of fluid

1. Crystalloid

Crystalloid fluid

A crystalloid fluids form a true solution meaning it can easily cross a semi permeable membrane and is distinguished by its ability to be crystallised. They can be classified asmaintainance or replacement fluids. A replacement crystalloid often do not have high potassium concentrations allowing for rapid administration without potassium toxicity, where as maintainance crystalloids often have a higher potassium but lower sodium and chloride then a replacement crystalloid.

0.9% Sodium Chloride

Also known as normal saline, 0.9% sodium chloride is often used as a replacement solution. It contains no further electrolytes. It has a higher chloride concentration then plasma. This can lead to a hyperchloremic acidosis which is unlikely to cause any problems in healthy patients but may cause further issues in compromised patients.

Hartmanns/Lactated Ringers

Hartmanns or Lactated Ringers Solution (LRS) is a balanced electrolyte solution. It also contains lactate which aids correction of acidosis. It also contains potassium and calcium. It also has a lower sodium concentration then plasma. Due to the calcium, it is not possible to administer LRS with blood products or sodium bicarbonate as it leads to clot/crystal formation. It is commonly used as a maintenance solution.

5% Dextrose

5% Dextrose consists of dextrose in water, and no electrolytes. It is rarely indicated for use during surgeries. It should not be used in patients thought to have cerebral injuries due to the deterimental affects the glucose will have.

2. Colloid solution

A colloid solution contains large molecules that do not easily cross a semi permeable membrane. Colloids can be either natural or synthetic. They are used to help maintain colloid osmotic pressure (COP), correct hypovolemia and with plasma (see below) clotting factors. It is the number of particles within the colloid that influences the osmotic effect, not the size of the particles. They are highly efficient at expanding vascular volume, compared to crystalloids, which easily diffuse out of the circulation, meaning that less volume is required

Dextran

Dextran is a molecule produced by certain strains of bacteria to give this linear polysaccaharide as either a high or low weight molecule. It is found in a sodium chloride or dextrose solution. It is metabolised to glucose within the patient. Both high and low weight molecules produce the same plasma volume expansion per gram, although the low weight molecule it thought to achieve this more rapidly. There are concerns about it's interaction with fibrin, making clots weaker and decreasing factor VIII and von Willebrand's factor.Examples include Dextran 40 and 70.

Hetastarch

Hetastarch is a synthetic glucose polymer, most commonly in a sodium chloride solution. Again, it is broken down into glucose in the patient. It is not as long in duration of action as dextran products but is still a very effective plasma volume expander. It can be used to draw fluid out of intersitium in patients with peripheral oedema or ascites. Again, there is some concern about prolonged bleeding times in patients who have received hetastarch products.Examples include Voluven.

Gelatin Solution

Gelatin solutions are derived from degradation of bovine collagen. It is found in several forms. Their advantage over other colloid solutions are their minimal effects on coagulation and minimal antigenic reactions. They have a lower molecular weight also.Examples include Haemaccel.

Blood Products

Whole Blood

Whole blood is administered when a patient requires all the components of whole blood. It contains clotting factors and active platelets and so requires correct storage. It is important to monitor patients receiving blood products closely in case of an anaphylactic reaction. Another concern with whole blood is the effect of citrate on the availability of calcium, which may require dosing also through a different line.

Plasma

Plasma is available as either a fresh or frozen product. Fresh plasma contains platelets and clotting factors, while fresh frozen plasma contains no platelets but does have clotting factors as long as it has been thawed correctly. Fresh frozen plasma can be used to expand the plasma volume, as long as the packed cell volume of that patient is within normal limits. However, there is always a concern when administering blood products of an anaphylactic reaction and so patients receiving these products should be closely monitored.

Fluid rate calculation

When calculating the fluid requirements of a patient, there are 3 elements to consider

Replacement
Maintainance
Ongoing Losses

For example of calculation refer here

Monitoring fluid therapy

Fluid therapy can be monitored by observing urine output, Packed Cell Volume (PVC), Total Protein (TP, or Total Solids, TS), mucous membrane colour, and blood pressure among others. It is important to also observe for signs of oedema, such as pulmonary oedema or ascites. It should not be stopped until hydration of the patient has returned to normal and the patient is able to maintain a normal hydration status independently.

Special consideration