Vet Clin Small Anim 38 (2008) 575–586

VETERINARY CLINICSSMALL ANIMAL PRACTICE

Fluid Therapy: Options and RationalAdministration

Steven Mensack, VMD*Pet Emergency Clinic, Inc., 2301 S. Victoria Avenue, Ventura, CA 93003, USA

Fluid support is a basic treatment for many hospitalized patients and someoutpatients. Proper use of fluids can be beneficial and even life saving.Fluids represent medication, however, and just as with any other medica-

tion, their inappropriate or injudicious use can lead to detrimental or eventragic outcomes. Fluid therapy is a complex topic, and this review is not meantto be all-encompassing. Rather, it provides general guidelines for effective fluidadministration in juvenile and adult small animal patients. There are manyexceptions to the basic tenets discussed here, including fluid therapy in neona-tal small animal patients.

PHYSIOLOGY OF BODY FLUIDSTo administer fluid therapy properly, a general understanding of where fluidsreside within the body and how they are lost during normal and abnormalphysiologic states is necessary. Sixty percent of the body in the average nonob-ese dog or cat is made up of water. This amount may vary slightly based on theage of the patient, species, or body composition (overweight patients havea higher water content). Of this 60%, approximately two thirds resides withinthe intracellular space (40% of body weight [BW]). The remaining one third oftotal body water comprises the interstitial and vascular fluid spaces. Of this20% of total BW, 5% of total body fluid resides in the intravascular spaceand 15% of total body fluid resides in the interstitial space [1].

Water and small dissolved solutes move among the fluid spaces in the bodybased on their concentration gradients and the osmotic effects of larger lessdiffusible macromolecules. The barriers for fluid movement among the differ-ent compartments vary; thus, different amounts of water and solutes are ableto move across these barriers. For example, the capillary walls are permeableto electrolytes and water, thus enabling water and small dissolved solutes tomove readily between the intravascular and interstitial fluid spaces. The move-ment of these fluids and electrolytes is governed by hydrostatic and oncoticforces (ie, Starling forces). The cellular membrane is freely permeable onlyto water and select small solutes, such as urea (serum urea nitrogen [BUN])

*202 Ashford Street, Brighton, MI 48114. E-mail address: criticalcarevet@comcast.net

0195-5616/08/$ – see front matter ª 2008 Elsevier Inc. All rights reserved.doi:10.1016/j.cvsm.2008.01.028 vetsmall.theclinics.com

576 MENSACK

and potassium, however. The movement of solutes other than urea and potas-sium into or out of the cell is a process of active transport. Water, urea, andpotassium move between the intracellular and interstitial spaces by means ofosmosis based on the gradient of less diffusible solutes across the cell mem-brane according to each compartment’s effective osmolality. Because ureaand potassium move by passive mechanisms, these molecules contribute littleto effective osmolality. The effective extracellular fluid osmolality can thusbe calculated by the formula:

2�Naþ þ Glucose18

Because of the different permeability properties of membranes (capillary andother cellular membranes), clinical signs of volume loss can vary depending onthe type and volume of fluid lost from the body. Loss of water in excess of sol-ute (hypotonic fluid loss) causes water to shift from the intracellular space intothe extracellular space, and ultimately into the intravascular space. The mostextreme types of hypotonic fluid loss include diabetes insipidus, excessive pant-ing, fever, and inadvertent water restriction. The most common causes of thistype of fluid loss include vomiting, diarrhea, and third space loss of fluids intobody cavities. With this type of fluid loss, signs of dehydration predominate.These signs include tacky or dry mucous membranes and decreased skin tur-gor with mild to moderate fluid losses. With loss of solute in excess of water(hypertonic fluid loss), water moves out of the intravascular and interstitialspaces into the cells by means of an osmotic gradient. With this type of fluidloss, signs of decreased perfusion and hypovolemia predominate. The mostcommon cause of this type of fluid loss is a secretory diarrhea commonlyencountered in hemorrhagic gastroenteritis. Signs may include pale mucousmembranes, bounding or hypodynamic pulses, and increases in heart rateand respiratory rate. Losses of water and solute in the same proportions asthose found within the extracellular space (isotonic fluid losses) produce effectson the intracellular and extracellular spaces in proportion to the total body fluidvolume. In these cases, signs of dehydration and intravascular hypovolemiacan be observed, although larger volumes of loss are needed to produce clinicalsigns. Finally, with loss of large volumes of intravascular fluid because of hem-orrhage, signs of intravascular hypovolemia are noted (as described for hyper-tonic fluid losses).

TYPES OF FLUIDSFive basic categories of fluid currently are available for intravenous use in smallanimal patients: crystalloids, colloids, hemoglobin-based oxygen-carrying solu-tions, blood products, and intravenous nutrition. Each of these fluid types hasspecific indications for its use.

Crystalloid fluids are the mainstay of fluid therapy. Crystalloid fluids consistprimarily of water with a sodium or glucose base, plus the addition of other

577FLUID THERAPY: OPTIONS AND RATIONAL ADMINISTRATION

electrolytes or buffers. The variable concentration of these different solutes dic-tates the use of a particular crystalloid in various clinical situations. Within thecrystalloid group, there are four different types of fluids: replacement solutions,maintenance solutions, hypertonic solutions, and dextrose in water. Replace-ment crystalloid solutions contain dissolved solutes that approximate the soluteconcentrations found in plasma water. These solutions are indicated for therapid replacement of intravascular volume and electrolytes, as seen with shockand hemorrhage or severe volume depletion secondary to losses associatedwith vomiting, diarrhea, third body space loss of fluid, or excessive diuresis.When using replacement crystalloid fluids, only 20% to 25% of the infusedvolume of fluid remains within the intravascular space 1 hour after infusion[2]. Therefore, large volumes of replacement crystalloids must be administeredto replace intravascular volume. The commonly available replacement solu-tions include normal saline (0.9% sodium chloride [NaCl]) and balanced elec-trolyte solutions, such as Ringer’s solution (with lactate or acetate),Normosol R (Hospira, Inc., Lake Forest, Illinois), and Plasmalyte A (BaxterHealthcare Corp., Deerfield, Illinois). Each type of replacement fluid listedhere has a different electrolyte composition and absence (ie, 0.9% NaCl) orpresence of different types of buffers (eg, lactate, acetate, gluconate) that makesits use in certain situations preferential, although not absolute [3].

Maintenance solutions also are composed of dissolved solutes that approxi-mate the solute concentration found in extracellular fluid. The difference inthese solutions compared with replacement solutions is that maintenance solu-tions are designed to fulfill the electrolyte requirements of patients with normaldaily electrolyte losses that are unable to maintain adequate fluid and electro-lyte intake [3]. Because these solutions are hypotonic, less than 10% of theinfused volume remains within the vascular space 1 hour after infusion. There-fore, they rarely are infused at rates greater than necessary to meet the patient’smaintenance needs. Commercially available maintenance fluid solutions in-clude half-strength saline (0.45% NaCl), half-strength saline and 2.5% dextrose,half-strength lactated Ringer’s solution and 2.5% dextrose, Normosol M (Hos-pira, Inc., Lake Forest, Illinois), and Plasmalyte 56 (Baxter Healthcare Corp.,Deerfield, Illinois). Commonly, maintenance solutions are supplemented withpotassium to balance them further for the patient’s electrolyte requirements.

Hypertonic saline (7.2%–23% NaCl) is used to increase intravascular volumerapidly. This effect is accomplished because of the high sodium content of thefluid. When hypertonic saline is infused, the increase in intravascular sodiumcauses fluid to shift from the interstitial space into the intravascular space inan attempt to normalize the intravascular sodium concentration. Most com-monly, hypertonic saline is used when severe hypovolemia is present andmay lead to impending death, when low-volume resuscitation is appropriate(eg, cerebral trauma Refs. [4,5]), or when large volumes of crystalloids cannotbe infused fast enough to have the desired rapid effect (eg, gastric dilatation-volvulus). Doses of 4 to 7 mL/kg (dogs) [6] or 2 to 4 mL/kg (cats) [7] ofa 7% solution infused at a rate of 1 mL/kg/min of hypertonic saline produce

578 MENSACK

a hemodynamic effect similar to infusion of 60 to 90 mL/kg of a replacementcrystalloid solution. Administration of hypertonic saline too rapidly has beenassociated with vagally mediated hypotension and bradycardia. Because ofrapid diffusion of sodium back out of the vasculature, the effect of hypertonicsaline is transient and only lasts up to 30 minutes [3]. To prolong this effect,hypertonic saline often is combined with a colloid to help keep fluid in the vas-cular space. Replacement crystalloid fluids should be administered after hyper-tonic saline to replace the fluid that was translocated into the vasculature.Contraindications for hypertonic saline include patients that are dehydrated(ie, inadequate interstitial fluid to draw into intravascular space), hyperosmolarpatients, hypokalemic patients, those that may develop problems with hypervo-lemia (ie, preexisting heart or lung disease), and those that have uncontrolledhemorrhage (eg, intracranial hemorrhage, intra-abdominal hemorrhage, pul-monary contusion) [8].

Five percent dextrose in water (D5W) is not commonly used in veterinarymedicine. Once the dextrose is metabolized, this fluid contains no active solute;therefore, it readily redistributes throughout the body. The most commonindications for D5W are as a vehicle for infusion of other medications andto provide free water in severe hypernatremic states. Infusion of large volumesof D5W can lead to dilution of serum electrolytes or development of edema.

Colloids are high-molecular-weight compounds that do not readily leave theintravascular space. They exert their effect of expanding intravascular volumeby holding and potentially drawing water into the vasculature [9,10]. Colloidalfluid solutions are indicated for rapid intravascular volume expansion in the treat-ment of hypovolemia; volume replacement for surgical blood loss; and low-volume resuscitation protocols, such as those advocated in patients that havecerebral trauma [4]. These solutions also are used to improve colloid osmotic (on-cotic) pressure in patients with low serum albumin concentration from proteinloss secondary to renal or gastroenteric disease or burns and in conditions inwhich proteins may leak into the interstitial spaces because of an inflammatoryresponse (eg, vasculitis, pancreatitis, sepsis). Colloid solutions include plasma;human serum albumin (5% and 25%); and synthetic compounds, such as hetas-tarch, dextrans, modified gelatin solutions, and stroma-free hemoglobin-basedoxygen-carrying solutions (Oxyglobin, Biopure Corp., Cambridge, Massachu-setts). Plasma use for strictly colloidal effects is relatively ineffective: a patientrequires plasma at a rate of approximately 50 to 100 mL/kg to raise serum albu-min concentration by 1 g/dL [11,12]. Therefore, synthetic compounds are a betterchoice for colloidal support. Contraindications and complications for the use ofcolloidal fluids include coagulopathies, potential for volume overload (eg, heartdisease, pulmonary disease, oliguric renal failure), and anaphylactic reactions.

Stroma-free, hemoglobin-based, oxygen-carrying solutions (Oxyglobin) arecolloidal solutions made of cross-linked bovine hemoglobin molecules. Thesefluids have the added benefit of allowing oxygen to be carried in the plasma,allowing transport of oxygen to areas in which red blood cells may be restricted(eg, traumatized tissue), and they do not depend on 2,3-diphosphoglycerate for

579FLUID THERAPY: OPTIONS AND RATIONAL ADMINISTRATION

oxygen unloading [13]. Indications for their use include volume resuscitationin shock or hypovolemic states and treatment of anemia. Hemoglobin-basedoxygen-carrying solutions also have been used in an extralabel manner inthe treatment of trauma, burns, severe wounds, sepsis, and other conditions.The greatest advantage of Oxyglobin is its ability to carry oxygen to the tissuesand offload oxygen more effectively because it is not limited by red blood cellflow. Other advantages of Oxyglobin are that it is a colloid; as such, it providesintravascular volume support. No blood typing or cross-matching is requiredbefore infusion; it also has been shown to improve microvascular perfusion,thus improving oxygen tension in injured tissues. Also, because it is a syntheticcompound, it has a long shelf life and does not require special storage proce-dures. Disadvantages of Oxyglobin are that certain clinical chemistry variablesare invalidated by its presence, laboratory monitoring of its effect requiresa hemoglobinometer, and its colloidal effect can lead to fluid overload andpulmonary edema if not monitored carefully (especially in cats). At this time,Oxyglobin is not approved for use in cats. According to the package insert,Oxyglobin has a flexible dosage range of 10 to 30 mL/kg, which allows theclinician to tailor therapy to the approximate duration of needed effect.

Blood products are indicated to replace red blood cells, plasma proteins,platelets, or coagulation factors. Blood products are available as whole bloodor components. The type of product needed is based on the component of pa-tient blood that needs to be replaced. For more specific information regardingthe proper selection and administration of blood products, consult one of themany excellent review articles on the subject [14–17].

Parenteral nutrition is considered for short- or long-term treatment in pa-tients whose clinical condition dictates that enteral nutrition is not feasible orwhen enteral nutrition may not provide sufficient nutrient intake to assistrecovery. Some of these conditions include severe pancreatitis, protracted vom-iting or regurgitation, extremely painful conditions, burns, sepsis, multipletrauma, or intestinal malabsorption. Parenteral nutrition can be providedthrough a peripheral or central vein. Elemental formulations of amino acids,lipids, carbohydrates, vitamins, and trace minerals are formulated for each pa-tient based on BW, type of injury or illness, duration of parenteral nutritionalsupplementation, and type of nutrition being administered. There are severaldifferent formulations of parenteral nutrition available. The most basic is a sup-plement consisting of a solution of amino acids and electrolytes in glycerol.This solution may be delivered through a peripheral vein and can supply upto 25% of basal metabolic needs [18]. Partial or peripheral parenteral nutrition(PPN) is delivered through a peripheral vein and can supply up to 50% of basalmetabolic needs [19]. Total parenteral nutrition (TPN) is delivered througha central vein and provides 100% of a patient’s basal nutritional needs [20].

REASONS FOR FLUID THERAPYWhen choosing a fluid type for the patient, an important question to askis: ‘‘What am I trying to accomplish?’’ The most common reasons for

580 MENSACK

administration of supplemental fluid therapy include replacing intravascularvolume deficits to improve tissue perfusion; replacing tissue interstitial volumedeficits (dehydration); meeting maintenance fluid needs in patients that are notconsuming sufficient quantities of fluid; and replacing ongoing losses attribut-able to vomiting, diarrhea, pneumonia, burns, severe wounds, and thirdbody space fluid accumulation. In most of these situations, crystalloid fluidtherapy is all that is required, although colloids or Oxyglobin can be beneficialin providing intravascular volume.

At certain times, fluid diuresis is required, such as with renal disease or tohasten elimination of toxins that are excreted by the kidneys. In these situa-tions, replacement crystalloid fluids are indicated. Rates required to induceadequate diuresis can be as high as 2.5 to 4.0 times a patient’s maintenancerequirements; however, ideally, the rate should be matched to urine output.

Fluid therapy also is indicated for patients undergoing anesthesia and sur-gery. Anesthetics commonly decrease vascular tone, cardiac output, or both.When this occurs, blood flow to the tissues is decreased (ie, poor perfusion).Fluid therapy increases vascular volume, thereby improving perfusion. Also,many surgical procedures cause enough blood loss to decrease intravascularvolume further. Commonly suggested replacement crystalloid fluid administra-tion rates for normovolemic patients undergoing anesthesia are 5 mL/kg/h forprocedures in which minimal blood loss is anticipated (eg, orthopedic surgery,uncomplicated soft tissue surgery) and 10 to 15 mL/kg/h for procedures inwhich moderate blood loss is anticipated (eg, soft tissue procedures, such asliver and splenic surgery) [21]. In surgical procedures in which the patient isunstable or may lose large volumes of blood, crystalloid fluids, colloid fluids,blood products, Oxyglobin, or some combination of these may be requiredat rates higher than those listed previously.

Fluid therapy also is appropriate when there is need for a specialized fluid. Insituations in which the patient is anemic, whole blood (fresh or stored), packedred blood cells, or Oxyglobin can be administered to provide oxygen-carryingmolecules. In situations in which the patient has a coagulopathy, regularly fro-zen plasma, fresh-frozen plasma, or cryoprecipitate can provide certain clottingfactors. Fresh-frozen plasma provides all clotting factors, and regularly frozenplasma provides all clotting factors except the most labile (ie, factors V andVIII). When a patient has low plasma protein concentration, such as may occurin protein-losing renal or intestinal disease, prolonged starvation, or vasculitis,fluids with large osmotically active particles, such as colloids, Oxyglobin, orplasma (fresh-frozen or regularly frozen), should be administered for oncoticsupport. Finally, intravenous nutritional solutions are indicated when the pa-tient is not able to consume sufficient food for a prolonged period.

HOW TO ADMINISTER FLUIDSParenteral fluid therapy is commonly administered as subcutaneous therapy, asa rapid intravenous bolus, or as an intravenous constant rate infusion. Fluidtherapy also can be administered by the intraosseous route in small patients

581FLUID THERAPY: OPTIONS AND RATIONAL ADMINISTRATION

in which venous access cannot be obtained or by the intraperitoneal route.Subcutaneous fluid therapy is indicated for the replacement of deficits, formaintenance needs, or to counteract ongoing losses. It is usually used on anoutpatient basis, because intravenous fluid therapy has been proved moreeffective in the hospital setting. Because only a limited amount of fluid canbe administered subcutaneously, this route cannot meet the daily fluid needsof most patients. It is best used in patients that are mildly dehydrated or mildlyhypovolemic Contraindications for subcutaneous fluid therapy include patientsthat are severely volume depleted because of dehydration or hypovolemia andhypothermic patients. In these situations, blood is shunted away from the sub-cutaneous vasculature, leading to poor and inconsistent absorption of adminis-tered fluids.

In the hospitalized setting, intravenous administration is the preferred routeof fluid therapy. Although convenient, determination of fluid therapy as a mul-tiple of ‘‘maintenance needs’’ is inappropriate, because most patients do notlose or require fluid in simple multiples of maintenance; at best, this approachprovides only a crude estimate of actual patient fluid requirements. Fluids maybe administered as a bolus or as a constant rate infusion. Bolus fluid therapy isindicated in severely volume-depleted and dehydrated patients. In the patientwith intravascular volume depletion, the volume of the bolus is determinedbased on resolution of clinical signs (eg, slower heart rate and respirations,improved pulse quality, improved mucous membrane color, improved capil-lary refill time) or improvement in other indicators of perfusion, such asacid-base status, serum lactate concentration, or gastric mucosal pH. Therefore,frequent reassessment of the volume-depleted patient is required. Crystalloidfluid rates up to 90 mL/kg/h in dogs and 60 mL/kg/h in cats or higher maybe required. Colloids also can be administered as boluses. Colloids are admin-istered in boluses of 5 to 40 mL/kg [22]. The patient should be reassessed aftereach bolus of crystalloid or colloid to determine if the bolus has been effectivein resolving volume depletion or if additional boluses are needed. Crystalloidfluids often are administered along with colloids to augment their vascular vol-ume-expanding effect. Smaller doses of crystalloids than those listed previouslyare necessary with the concomitant use of colloid. In the dehydrated patient,the quantity of a fluid bolus is based on the estimated degree of dehydration.The dehydration deficit can be calculated as: BW (kg) � Estimated Degreeof Dehydration (%) � 100 ¼ mL of Fluid Required. One half of the dehydra-tion deficit should be administered as a bolus, and the remainder should bereplaced as a constant rate infusion over 12 to 24 hours.

Constant rate fluid administration is indicated in several situations. As de-scribed previously, it is used to replace dehydration deficits. It is also necessaryto account for a patient’s maintenance fluid requirements if the patient is notconsuming sufficient quantities of fluid on its own. Daily maintenance needsfor patients varies based on the age and size of the patient. Maintenance crystal-loid fluid needs traditionally have been considered to be 54 to 66 mL/kg/d (withthe lower end of the range applying to large dogs and the higher end to small

582 MENSACK

dogs and cats) [23]. In the pediatric patient, fluid requirements may be as highas 180 mL/kg/d [24]. Veterinarians may be overestimating our patients’ main-tenance fluid needs, however. Several studies have evaluated basal metabolicrate and used indirect calorimetry with limited success in an attempt todetermine actual fluid requirements [25,26]. Based on these studies, the dailymaintenance fluid requirement for a healthy cat or dog weighing between2 and 70 kg is as follows: (30 � BW [kg]) þ 70 (Figs. 1 and 2) [25]. Using6% hydroxyethyl starch (hetastarch) colloid fluid therapy, infusions of20 mL/kg/d (dog) [15,18] or 10 to 40 mL/kg/d (cat) [22] have been used toprovide continuous intravascular volume support. With the infusion of colloids,lower infusion rates of crystalloids are necessary. If a patient has ongoing lossesattributable to vomiting, diarrhea, third space fluid accumulation (eg, ascites,pleural effusion), or diuresis (eg, postobstructive diuresis; glucosuria; diseasesthat cause polyuria, such as hyperadrenocorticism or renal failure), these lossesshould be replaced with 2 mL of crystalloid per 1 mL of fluid lost [27].

Administration of specialized fluids, such as natural and synthetic colloids,blood products, and intravenous nutrition, is covered in other excellent reviewarticles [14–17,19,28–33]. Because blood products and nutrition are providedintravenously and there is a higher potential for complications comparedwith other forms of fluid therapy, patients receiving blood products or paren-teral nutrition require hospitalization and extensive monitoring.

MONITORING FLUID THERAPYAs with any other medication, monitoring for the desired effect and for poten-tial adverse effects is necessary during fluid administration. Proper monitoring

Fig. 1. Daily water requirements for the dog. The recommended formula is as follows: (30 �kg BW) þ 70. This formula closely approximates findings of indirect calorimetry (90.29 �kg0.75) in the dog. (From Wingfield WE, Raffe MR. The veterinary ICU book. Jackson (WY):Teton NewMedia; 2002. p. 176; with permission.)

Fig. 2. Estimating fluid requirements for the cat. The recommended formula is as follows: (30� kg BW) þ 70. (From Wingfield WE, Raffe MR. The veterinary ICU Book. Jackson (WY):Teton NewMedia; 2002. p. 177; with permission.)

583FLUID THERAPY: OPTIONS AND RATIONAL ADMINISTRATION

of the patient receiving fluids is a ‘‘hands-on’’ endeavor. Much of the necessaryinformation is gained by serial examination of the patient. No single evaluatedvariable can provide all the information required to guide fluid therapyproperly. Physical examination findings that should be evaluated include thepatient’s weight, physical appearance, mentation, skin turgor, pulse rate andquality, respiratory rate and effort, serial lung auscultation for crackles, mucousmembrane color, and capillary refill time. Skin turgor allows for gross assess-ment of hydration status. Skin turgor is notably prolonged with 6% to 8% de-hydration and markedly prolonged with greater than 8% dehydration. Bodycondition can limit the effectiveness of skin turgor assessment, because obesitycan mask decreases in skin turgor and emaciation may artifactually worsenskin turgor. If an indwelling urinary catheter is in place, serial evaluation offluid input and urine output can provide useful information about whethertoo little or too much fluid has been administered.

Cage-side testing and conventional laboratory testing should be used in com-bination with assessment of vital parameters. Renal function parameters (eg,BUN and serum creatinine concentrations, urine specific gravity) provide addi-tional useful information. Increased BUN and serum creatinine concentrations,in conjunction with increased urine specific gravity (ie, prerenal azotemia), mayindicate that a patient is receiving insufficient amounts of fluid. Blood gas anal-ysis or measurement of serum lactate concentration [34] can provide informa-tion about tissue perfusion. Metabolic acidosis or increased serum lactateconcentration may indicate that tissues are not receiving adequate oxygen formetabolism and instead are relying on anaerobic metabolism to provide energy.The clinical standard in veterinary medicine for evaluating adequacy of fluidtherapy is serial central venous pressure (CVP) measurement, which approxi-mates the ability of the right side of the heart to pump blood forward. Thismethod allows the clinician to make adjustments to fluid type and rate based

584 MENSACK

on the ability of the patient’s heart to handle the infused volume [35]. Perform-ing CVP measurement is well covered in many review articles on fluid therapymonitoring [36,37]. Monitoring of the patient receiving intravenous fluid ther-apy should involve a combination of these tests to ensure adequate volume sta-tus and to help prevent inadequate resuscitation or volume overload.

CONTRAINDICATIONS FOR FLUID THERAPYIn some situations, fluid therapy is not necessarily in the best interest of thepatient. The most common situation is the patient that has congestive heart fail-ure. In this situation, the patient develops congestion because the heart is notable to pump the volume it currently has presented to it effectively. Heartdisease is not an absolute contraindication to fluid therapy, however. Insome situations, there may be concomitant dehydration or a need for medica-tions infused by constant rate infusion to treat the heart disease, and judicioususe of fluid therapy may be warranted. In these patients, hypotonic mainte-nance crystalloids or, less commonly, D5W is indicated. Meticulous monitor-ing of vital parameters, urine output, and CVP is necessary for successfuluse of fluid therapy in patients that have congestive heart failure.

The other situation when fluid therapy may not be necessary is when thepatient is already consuming adequate volumes of water and is normallyhydrated. In this situation, fluid therapy may lead to dilution of blood compart-ment constituents, renal medullary solute washout, or development of pulmo-nary edema if occult heart disease is present. Even in this situation, however,fluid therapy may be warranted if diuresis is indicated because of ingestion ofa toxin or if a medication must be administered by constant rate infusion.

DISCONTINUATION OF FLUID THERAPYDiscontinuing fluid therapy is as important as initiating fluid therapy. In mostinstances, fluid therapy should not be abruptly discontinued, especially if thepatient is receiving high flow rates. During fluid therapy, the solute gradientin the kidneys may be changed as a result of fluid therapy (ie, renal medullarysolute washout). If fluid therapy is abruptly discontinued, the patient may notbe able to concentrate urine well and may continue to lose excessive fluid in theurine for several days. This can be a serious problem if the patient is not ingest-ing adequate amounts of water and may lead to dehydration. The patientshould be gradually weaned from fluid therapy. In the ideal situation, fluidtherapy should be tapered to lower than maintenance for at least 24 hoursbefore discontinuation of fluid therapy. This approach is not always possible,however. If fluid therapy must be abruptly discontinued, the patient shouldhave access to adequate quantities of water and the owner should be informedof the patient’s increased water requirements over the next several days.

As stated throughout, the overview presented here is not meant to be com-prehensive and exceptions to many of the ‘‘rules of thumb’’ presented here doexist. The most important caveat is that there is no set formula for fluid admin-istration, and the clinician must tailor fluid composition and rate of

585FLUID THERAPY: OPTIONS AND RATIONAL ADMINISTRATION

administration to the patient’s needs as required by its clinical condition andresults of parameters that are monitored. Careful monitoring of patients receiv-ing fluid therapy is required to ensure a successful outcome.

References

[1] Wellman ML, DiBartola SP, Kohn CW. Applied physiology of body fluids in dogs and cats.

In: DiBartola SP, editor. Fluid, electrolyte, and acid-base disorders in small animal practice.3rd edition. St. Louis (MO): Saunders Elsevier; 2006. p. 3–26.

[2] Griffel MI, Kaufman BS. Pharmacology of colloids and crystalloids. Crit Care Clin1992;8(2):235–53.

[3] Mathews KA. The various types of parenteral fluids and their indications. Vet Clin North AmSmall Anim Pract 1998;28(3):483–513.

[4] Ducey JP, Mozingo DW, Lamiell JM, et al. A comparison of the cerebral and cardiovasculareffects of complete resuscitation with isotonic and hypertonic saline, hetastarch, and wholeblood following hemorrhage. J Trauma 1989;29(11):1510–8.

[5] Dewey CW, Budsberg SC, Oliver JE. Principles of head trauma management in dogs andcats—part II. Compendium of Continuing Education for the Practicing Veterinarian1993;15(2):177–93.

[6] Schertel ER, Allen DA, Muir WW, et al. Evaluation of a hypertonic saline-dextran solution fortreatment of dogs with shock induced by gastric dilatation-volvulus. J Am Vet Med Assoc1997;210:226–30.

[7] Muir WW, Sally J. Small-volume resuscitation with hypertonic saline solution in hypovolemiccats. Am J Vet Res 1989;50(11):1883–8.

[8] Krausz MM. Controversies in shock research: hypertonic resuscitation—pros and cons.Shock 1995;3(1):69–72.

[9] Thompson WL, Fukushima T, Rutherford RB, et al. Intravascular persistence, tissue storage,and excretion of hydroxyethyl starch. Surg Gynecol Obstet 1970;131(5):965–72.

[10] Khosropur R, Lackner F, Steinbereithner K, et al. Comparison of the effect of pre- and intra-operative administration of medium molecular weight hydroxyethyl starch (HES 200/0.5)and dextran 40(60) in vascular surgery. Anaesthesist 1980;29(11):616–22.

[11] Mazzaferro EM, Rudloff E, Kirby R. The role of albumin replacement in the critically illveterinary patient. Journal of Veterinary Emergency Care 2002;12(2):113–24.

[12] Logan JC, Callan MB, Drew K, et al. Clinical indications for the use of fresh frozen plasma indogs: 74 dogs (October through December 1999. J Am Vet Med Assoc 2001;218(9):1449–54.

[13] Fronticelli C, Bucci E, Orth C. Solvent regulation of oxygen affinity in hemoglobin. Sensitiv-ity of bovine hemoglobin to chloride ions. J Biol Chem 1984;259:10841–4.

[14] Haldane S, Roberts J, Marks SL, et al. Transfusion medicine. Compendium of ContinuingEducation for the Practicing Veterinarian 2004;26(7):502–18.

[15] Hughes D, Boag A. Fluid therapy with macromolecular plasma volume expanders. In:DiBartola SP, editor. Fluid, electrolyte, and acid-base disorders in small animal practice.3rd edition. St. Louis (MO): Saunders Elsevier; 2006. p. 621–34.

[16] Griot-Wenk ME, Giger U. Feline transfusion medicine. Vet Clin North Am Small Anim Pract1995;25(6):1305–22.

[17] Kristensen AT, Feldman BF. General principles of small animal blood component administra-tion. Vet Clin North Am Small Anim Pract 1995;25(6):1277–90.

[18] Freeman JB, Fairful-Smith R, Rodman GH, et al. Safety and efficacy of a new peripheralintravenously administered amino acid solution containing glycerol and electrolytes. SurgGynecol Obstet 1983;156(5):625–31.

[19] Zsombor-Murray E, Freeman LM. Peripheral parenteral nutrition. Compendium of Continu-ing Education for the Practicing Veterinarian 1999;21(6):512–23.

[20] Remillard RL, Thatcher CD. Parenteral nutritional support in the small animal patient. Vet ClinNorth Am Small Anim Pract 1989;19(6):1287–306.

586 MENSACK

[21] Kudnig ST, Mama K. Guidelines for perioperative fluid therapy. Compendium of ContinuingEducation for the Practicing Veterinarian 2003;25(2):102–11.

[22] Rudloff E, Kirby R. Colloids: current recommendations. In: Bonagura JD, editor. Currentveterinary therapy XIII. Philadelphia: WB Saunders; 2000. p. 131–6.

[23] Garvey MS. Fluid and electrolyte balance in critical patients. Vet Clin North Am Small AnimPract 1989;19(6):1021–57.

[24] Mosier JE. Canine pediatrics—the neonate. Journal of the American Animal Hospital Asso-ciation 1981;48:339–47.

[25] Wingfield W. Fluid and electrolyte therapy. In: Wingfield W, editor. The veterianry ICUbook. Jackson (WY): Teton NewMedia; 2002. p. 166–88.

[26] Olgilvie GK, Salman MD, Kessel ML, et al. Effect of anesthesia and surgery on energyexpenditure determined by indirect calorimetry in dogs with malignant and nonmalignantconditions. Am J Vet Res 1996;57(9):1321–6.

[27] Greco DS. The distribution of body water and general approach to the patient. Vet ClinNorth Am Small Anim Pract 1998;28(3):473–82.

[28] Day TK. Current development and use of hemoglobin-based oxygen-carrying (HBOC)solutions. Journal of Veterinary Emergency Care 2003;13(2):77–93.

[29] Kerl ME, Cohn LA. Albumin in health and disease: causes and treatment of hypoalbumine-mia. Compendium of Continuing Education for the Practicing Veterinarian 2004;26(12):940–8.

[30] Martin L. Human albumin solutions in the critical patient. Proceedings of the InternationalVeterinary Emergency and Critical Care Society 2004;274–8.

[31] Mathews KA, Barry M. The use of 25% human serum albumin: outcome and efficacy inraising serum albumin and systemic blood pressure in critically ill dogs and cats. Journalof Veterinary Emergency Care 2005;15(2):110–8.

[32] Rudloff E, Kirby R. The critical need for colloids: selecting the right colloid. Compendium ofContinuing Education for the Practicing Veterinarian 1997;19(7):811–25.

[33] Rudloff E, Kirby R. The critical need for colloids: administering colloids effectively. Compen-dium of Continuing Education for the Practicing Veterinarian 1998;20(1):27–43.

[34] Karagiannis MH, Reniker AN, Kerl ME, et al. Lactate measurement as an indicator ofperfusion. Compendium of Continuing Education for the Practicing Veterinarian2006;28(4):287–98.

[35] Jennings PB, Anderson RW, Martin AM. Central venous pressure monitoring: a guide toblood volume replacement in the dog. J Am Vet Med Assoc 1967;151(10):1283–93.

[36] Hansen BD. Technical aspects of fluid therapy. In: DiBartola SP, editor. Fluid, electrolyte, andacid-base disorders in small animal practice. 3rd edition. St. Louis (MO): Saunders Elsevier;2006. p. 344–76.

[37] Oakley RE, Olivier B, Eyester GE, et al. Experimental evaluation of central venous pressuremonitoring in the dog. J Am Anim Hosp Assoc 1997;33(1):77–82.