© 2004 by Thomson Delmar Learning, a part of the Thomson Corporation. Fundamentals of Pharmacology for Veterinary Technicians Chapter 19 Fluid Therapy.

Fundamentals of Pharmacology for Veterinary Technicians

Chapter 19

Fluid Therapy and Emergency Drugs

Basics of Body Fluid

• Water is the primary body fluid• Body water is distributed among three

types of compartments: intracellular, intravascular, and interstitial– Intracellular fluid (ICF) = fluid within the cell

(two-thirds of body water)– Extracellular fluid (ECF) = fluid within the

blood vessels and in the tissue spaces between the blood vessels and cells (one-third of body fluid)

Basics of Body Fluid

• Body water contains solutes (substances that dissolve in solvent; particles)– Electrolytes are substances that split into ions

when placed in water– Primary ions in the body are sodium,

potassium, chloride, phosphate, and bicarbonate

• Cations are positively charged ions• Anions are negatively charged ions

• Body water is the solvent in biological systems• To establish equilibrium, body water moves along

its concentration gradient

Basics of Body Fluid

• Extracellular fluid shifts between the intravascular space (blood vessels) and the interstitial space (tissues) to maintain a fluid balance with the ECF compartment

• Fluid exchange occurs only across the capillary walls

• Fluid therapy in animals may involve the use of crystalloids and/or colloids

• Crystalloids are diffusible substances that dissolve in solution

• Colloids are nondiffusible substances

Fluid Therapy

• The basis for fluid therapy depends on the animal’s hydration status (see Table 19-1)

• Fluid therapy can replace water, sodium, potassium, and chloride electrolytes, and restore hydrogen ion balance (pH balance)

Routes of Fluid Administration

Route of administration

Advantages Disadvantages

Oral •Safest route•Easy

•Less rapid absorption•Possible aspiration•Cannot use for vomiting animals

Subcutaneous •Relatively easy to administer•Absorption distributed over time

•Possible infection•Must use isotonic fluids•Slower absorption

Routes of Fluid AdministrationRoute of administration

Advantages Disadvantages

Intravenous •Precise amount given is available rapidly •Various tonicities of fluid can be used

•Possible fluid overload and vessel damage•Requires close monitoring•Must be sterile

Intraperitoneal •Relatively rapid absorption•Can be used when IV access is not available

•Possible infection•Cannot use hypertonic solutions•Abdominal surgery hindered after administration

Routes of Fluid Administration

Route of administration

Advantages Disadvantages

Intraosseous •Useful for small animals, birds, and pocket pets•Can be used when vein inaccessible•Rapid absorption

•Lack of confidence in administering fluid via this route•Possible infection

Rectally •Good absorption•Rapid absorption

•Not frequently used

Tonicity of Fluids

• Tonicity refers to the osmotic pressure of a solution based on the number of particles per kilogram of solution (osmolality)

• An isotonic solution has the same osmotic pressure as blood and extracellular water

• A hypotonic solution has osmolality lower than that of blood; RBCs can swell

• A hypertonic solution has osmolality higher than that of blood; RBCs can shrink

Types of Crystalloids

• Isotonic– 0.9% sodium chloride (normal saline)– Lactated Ringer’s solution– Normosol– Plasmalyte

• Hypotonic– 5% dextrose in water (D5W)– ¼ NS (0.25% normal saline)– ½ NS (0.45% normal saline)

• Hypertonic– 0.9% normal saline with 5% dextrose– 10% dextrose in water– 3% normal saline

Types of Colloids

• Colloid solutions are fluids with large molecules that enhance the oncotic force of blood, causing fluid to move from the interstitial and intracellular spaces into the vascular space

• Natural– Plasma– Albumin– Whole blood

• Synthetic– Dextrans– Hydroxyethyl starch– Oxypolygelatin

Fluid Additives

• Special additives can be supplemented to crystalloid solutions

• When administering additives, it is important to remember to withdraw and discard an amount of fluid equal to the amount of additive being supplemented

• Types of additives:– 50% dextrose– Potassium– Sodium bicarbonate– Calcium– Vitamins

Calculating Fluid Volumes

• Must consider that animals require fluids for the following:– Rehydration– Maintenance– Ongoing fluid loss

• Make sure the units of measure are the same when performing these calculations

• Make sure the volumes make sense; we don’t give 1,000 liters to a 4-pound cat

Calculating Fluid Volume

• Example: An adult 14-lb cat with 3% dehydration comes into the clinic. It is estimated that the cat vomited 100 ml of fluid overnight

• Maintenance fluid is the volume of fluid needed daily to maintain body function

• Maintenance fluids can be dosed at 50 ml/kg/day in adults and 110 ml/kg/day in young animals

• Step 1: Convert 14 lb to kg using the conversion factor 2.2 lb = 1 kg

14 lb x 2.2 lb/kg = 6.4 kg

• Step 2: Calculate maintenance volume

6.4 kg x 50 ml/kg/day = 318 ml per day

Calculating Fluid Volume• Example: An adult 14-lb

cat with 3% dehydration comes into the clinic. It is estimated that the cat vomited 100 ml of fluid overnight

• Rehydration fluid is based on the estimated percent of dehydration % dehydration x weight in kg

= deficit in liters

• Step 1: Convert 14 lb to kg using the conversion factor 2.2 lb = 1 kg14 lb x 2.2 lb/kg = 6.4 kg

• Step 2: Calculate replacement for dehydration3% = 0.030.03 x 6.4 kg = 0.192 l0.192 l x 1,000 ml/l = 192 ml192 ml x 0.8 (80% of

dehydration value replaced in 24 hours) = 154 ml to replace on first day

Calculating Fluid Volume

• Example: An adult 14-lb cat with 3% dehydration comes into the clinic. It is estimated that the cat vomited 100 ml of fluid overnight

• Ongoing fluid loss is an estimation based on the additional loss of fluid due to vomiting or diarrhea

• Take estimated volume

• Step 1: Take estimated volume lost in fluid and add to the other volumes

• Final step: Take all values and add together318 ml + 154 ml + 100 ml

= 572 ml

How and How QuicklyIs It Given?

• Rate of fluid replacement parallels the severity of dehydration

• Ideally, fluids are given over a 24-hour period• Fluids are stored and given by fluid bags or

bottles attached to administration sets• Fluids are administered with either:

– An adult administration set that delivers 15 gtt/ml (usually)

– A pediatric administration set that delivers 60 gtt/ml (usually)

– See text and “Fluid & Electrolytes for Veterinary Technicians” CD for sample calculations

Emergency Drugs

• In an emergency situation, it is important to remember basic life support– A = airway = establish a patent airway

(endotracheal tube, suctioning, tracheostomy) – B = breathing = provide oxygen to the patient

by providing airway or mechanical ventilation– C = circulation = get blood moving, either by

manual manipulation of the heart or by the use of drugs

• See Table 19-3