Fluid Therapy

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Vol. 25, No. 2 February 2003 Comments? Questions? Email: [email protected] Web: VetLearn.com • Fax: 800-556-3288

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Article #2 (1.5 contact hours) Refereed Peer Review

Guidelines for Perioperative Fluid Therapy KEY FACTS Colorado State University ■ Perioperative fluid therapy is an important component of hemodynamic stabilization to minimize drug-exacerbated hypotension and risks related to anesthesia. ■ Preoperative resuscitation of the intravascular fluid compartment is of prime importance to improve preload, stroke volume, and cardiac output, all of which are suppressed by most anesthetics. ■ Use of synthetic and natural colloids for resuscitation reduces the required volume of crystalloids and helps retention of administered fluids in the intravascular space. ■ Repeated evaluation of physical examination and laboratory parameters is important to ensure adequate fluid replacement and perfusion, prevent overhydration or hypervolemia, and ensure use of the appropriate fluid.

Simon T. Kudnig, BVSc, MVS, MACVSc Khursheed Mama, DVM, DACVA ABSTRACT: The fluid therapy plan should be tailored to the requirements of each surgical patient and pertains to preoperative, intraoperative, and postoperative periods. Fluid therapy plans for compromised and healthy patients differ widely. Fluid therapy plans also differ according to the type of surgical procedure. This article provides guidelines for perioperative fluid therapy, outlines the methods of fluid administration, and discusses the monitoring techniques used during blood volume replacement in the surgical patient. Specific suggestions for various populations and disorders are also presented in tabular form.

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he following questions must be considered before implementing a perioperative fluid therapy plan: Is fluid administration necessary? What type of fluid is appropriate? How fast and by what route should fluid be administered? Are fluid additives necessary? A number of factors influence these questions, including the status of the patient’s fluid, electrolyte, and acid–base balances; the stage of the perioperative period; the pathophysiologic changes associated with disease; and whether oxygen delivery to peripheral tissues is compromised (if so, is it a result of a deficiency in blood oxygen content or cardiac output?). Perioperative assessment of these factors and the physiologic changes associated with anesthetic agents enables a clinician to formulate a specific perioperative fluid therapy plan. Changes in the fluid therapy requirements of a patient can occur rapidly, emphasizing the need for appropriate monitoring techniques to enable prompt and precise adjustments to the fluid therapy plan.

PREOPERATIVE FLUID THERAPY The cardiovascular status of surgical patients should be stabilized as much as possible before anesthesia. Fluid therapy is an important component of this hemodynamic stabilization to minimize drug-exacerbated hypotension and risks related to anesthesia. Preoperative evaluation of a patient includes an assessment for deficits of the intravascular fluid compartment that manifest in hypoperfusion and of the interstitial and intracellular fluid compartments that result in dehydration (see Monitoring Fluid Therapy, p. 109). Electrolyte and acid–base imbalances can further compromise the cardiovascular status of an anesthetized patient and should be corrected before surgery.1–3 In an emergency, mild metabolic, electrolyte, and acid–base disorders may be corrected in the intraoperative and postoperative periods. However, extreme hyperkalemia (potassium concen-

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tration >8 mmol/L), acidemia (pH ≤7.20), or hypoglycemia (blood glucose value ≤60 mg/L) should be corrected preoperatively. 4 Management of acid–base and electrolyte disorders has been reviewed elsewhere.5–9 Guidelines for treating common electrolyte disorders are given in the box on this page. Preoperative resuscitation of the intravascular fluid compartment is of prime importance to improve preload, stroke volume, and cardiac output, all of which are compromised by most anesthetic drugs.10–11 Isotonic crystalloid replacement solutions may be used to treat mild to moderate hypovolemia, with resuscitation fluid quantities up to one blood volume (50 to 90 ml/kg IV in dogs, and 40 to 60 ml/kg IV in cats). The intravascular space can be resuscitated by administering incremental fluid boluses of isotonic crystalloids at 10 to 20 ml/kg IV, with reassessment of hemodynamic parameters (heart rate, arterial blood pressure) and physical parameters between boluses. Synthetic colloids may be added to resuscitation flu-

ids to reduce the required volume of isotonic crystalloids and to help retain administered fluids in the intravascular space. The use of synthetic colloids is important in moderate to severe hypovolemic shock because larger intravascular fluid deficits often coincide with an increase in capillary permeability.12 A rapid IV infusion of isotonic crystalloids at 40 to 50 ml/kg/hr (half of one blood volume) and a bolus injection of hetastarch (Hespan [hetastarch 6% in 0.9% sodium chloride], B. Braun Medical; Hetastarch [hetastarch 6% in 0.9% sodium chloride injection], Baxter Healthcare Corp.) or dextran 70 (6% Gentran 70, Baxter Healthcare Corp.; dextran 70, B. Braun Medical; Macrodex, Medisan) up to 10 to 20 ml/kg IV are recommended for initial resuscitation of severely hypovolemic dogs.13 In cats with hypovolemic shock, a rapid IV infusion of isotonic crystalloids at 10 to 30 ml/kg/hr combined with hetastarch or dextran 70 at 5 ml/kg, administered over 5 to 10 minutes, has been recommended for initial fluid resuscitation.13

Guidelines for Treating Common Perioperative Electrolyte and Glucose Disorders Hypokalemia • Do not administer potassium at a rate >0.5 mEq/kg/hr. • Guidelines for potassium supplementation of fluids given at a maintenance rate:

Hypocalcemia • Treat acute hypocalcemia with up to 15 mg/kg slow IV of elemental calcium (10% calcium gluconate, 9.3 mg of calcium/ml) at 0.5–1.5 ml/kg.

Serum Potassium Level mEq Potassium Chloride (mEq/L) (add to 1 L of crystalloids) <2.0 80 2.1–2.5 60 2.6–3.0 40 3.1–3.5 30 3.6–5.0 20 • Avoid potassium supplementation of intraoperative fluids because of the risk of potassium toxicity when a fluid bolus is given to treat hypotension. Administration via a CRI is preferred.

• Do not administer the calcium too rapidly because of possible adverse cardiovascular effects, and monitor the electrocardiogram during administration.

Hyperkalemia • Use physiologic saline or balanced electrolyte solutions to reduce potassium levels. • Use sodium bicarbonate (0.5–1.0 mEq/kg IV) to treat acute hyperkalemia.

or • Give 50% dextrose (0.5–1.0 g/kg over a few minutes). • Regular insulin (0.5–1 IU/kg) plus 50% dextrose (2.0 g/U of insulin) can be administered for severe cases. • Use 10% calcium gluconate (9.3 mg of calcium/ml; 0.5–1.5 ml/kg IV over 10–20 min) for lifethreatening bradyarrhythmias.

• A follow-up CRI at 10 mg/kg/hr can be used if necessary. Hypomagnesemia • Do not add magnesium chloride to calciumcontaining solutions. • Supplement crystalloids with magnesium (e.g., magnesium sulfate) at a rate of 0.75–1.0 mEq/kg/day. Hypoglycemia • Treat the underlying cause of hypoglycemia. • In patients with severe hypoglycemia (glucose level <60 mg/dl) and neurologic signs, a bolus injection of 50% dextrose is recommended at 1 ml/kg followed by a CRI of 2.5% or 5% dextrose.

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Low-volume resuscitation with hetastarch and crystalloids has been proposed for patients with cerebral hemorrhage or edema, pulmonary hemorrhage or edema, hypovolemic cardiac insufficiency, or chronic hypoalbuminemia.13–15 While efforts are made to treat the primary disease, hetastarch is administered at a rate of 5 ml/kg IV, over 5 to 10 minutes, combined with maintenance rates of crystalloids (see Postoperative Fluid Therapy, p. 108). These patients are poorly tolerant of interstitial edema, and administration of large volumes of crystalloids should be avoided. The role of synthetic colloid therapy in pulmonary edema is controversial, however, because pulmonary edema may worsen if increased pulmonary endothelial permeability allows colloid molecules to pass into the interstitium.16 Potential side effects of treatment with synthetic colloids include circulatory overload, coagulopathies, anaphylactic reactions, and hyperosmotic renal dysfunction.17 The possible effects of synthetic colloid solutions on platelet function can be monitored by means of the buccal mucosal bleeding time; the effect on factor VIII and von Willebrand’s factor can be evaluated via partial thromboplastin time. This monitoring is especially important when multiple synthetic colloid transfusions are administered. Hypertonic saline (7% to 7.5%) can be used for the restoration of intravascular volume in patients with severe hypovolemic shock or evidence of head trauma.18–20 An IV bolus of 1 to 4 ml/kg in cats and 4 to 8 ml/kg in dogs is administered over 10 minutes and should be followed by a crystalloid or synthetic colloid to augment the volume restoration achieved by the saline.4,21 The use of a colloid and hypertonic saline in combination, rather than isotonic crystalloids, has been advocated to reduce the overall volume of fluid required for resuscitating patients in shock.20,22,23 If hypertonic saline is given too rapidly, hypotension caused by direct vascular relaxation and vasodilation may occur and can be fatal.24 In patients with cardiac disease, lower doses of hypertonic saline along with central venous pressure (CVP) monitoring are recommended to prevent circulatory overload. The use of hypertonic saline should be avoided in patients with severe dehydration and hyperosmolar conditions.18 Patients suffering from acute hemorrhage should be resuscitated with whole blood, packed red blood cells (RBCs), or an autotransfusion of blood (if a septic or neoplastic cause is not present) to restore the oxygencarrying capacity of the blood. The packed cell volume (PCV) and hemoglobin content should be increased to a minimum of 20% and 7 mg/dl, respectively, although a minimum PCV of 25% to 30% is recommended for surgical patients.4,25 Any patient receiving blood prod-

ucts should be observed for immediate transfusion reactions, including anaphylactic shock, pyrexia, urticaria, restlessness, salivation, vomiting, fecal and urinary incontinence, and apnea. Oxygen-carrying solutions, such as Oxyglobin (Biopure Corp.), may have a role in resuscitation from hemorrhagic shock.26 Oxyglobin has been shown to be more potent than autologous RBCs for restoring tissue oxygenation after isovolemic hemodilution in dogs because of more pronounced extraction of oxygen from the ultrapurified polymerized bovine hemoglobin molecule. 26 The colloid osmotic pressure of Oxyglobin, however, is higher than that of hetastarch, which may cause circulatory overload and pulmonary edema if Oxyglobin is administered too rapidly.27 Successful treatment of hypovolemia is manifested as an improvement in cardiovascular and clinical parameters, as discussed later (see Monitoring Fluid Therapy, p. 109). Subsequent to resuscitation of the intravascular fluid compartment, a patient’s interstitial fluid deficit or hydration status is calculated (see Postoperative Fluid Therapy section, p. 108). A patient should ideally be completely rehydrated before anesthesia and surgery, but many diseases necessitate immediate surgical intervention. In these cases, after the intravascular compartment is resuscitated and the patient is hemodynamically stable, anesthesia and surgery may proceed. Correction of interstitial fluid deficits then becomes a priority in the postoperative period.

INTRAOPERATIVE FLUID THERAPY Intraoperative fluid therapy is a continuation of preoperative fluid therapy but with the compounding effects of anesthesia and surgery on hemodynamic stability. The role of routine fluid therapy for healthy patients undergoing routine procedures has been questioned, 28–29 although perioperative fluid therapy for human surgical outpatients decreases adverse effects, such as thirst, dizziness, and drowsiness.30 A dosage rate for intraoperative isotonic crystalloid fluids that is widely recommended to offset the effects of hypotension and maintain perfusion during anesthesia is 10 to 15 ml/kg/hr IV. 31 However, lower rates of fluid administration (3 to 5 ml/kg/hr IV) may be adequate for many healthy patients after the first hour of anesthesia. Prewarming fluids to body temperature before infusion is recommended for anesthetized patients, particularly smaller ones that are more prone to intraoperative hypothermia because of a high surface area:body weight ratio. IV boluses of polyionic fluids of 10 to 15 ml/kg are recommended as a first-line therapy for hypotension in anesthetized patients with normal PCV and total pro-

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tein (TP) values, subsequent to an adjustment of anesthetic depth. Fluid boluses deliver volume directly to the fluid compartment requiring expansion, and time for redistribution to the interstitial and intracellular fluid compartments is not required. Fluid overload should be avoided, however, because postoperative fluid overload has been associated with increased invasive monitoring requirements and mortality in humans.32 For animals with hypotension that is refractory to isotonic crystalloid therapy, the use of synthetic colloids, rather than excessive administration of isotonic crystalloid fluids, should be considered. In some cases, expanding the intravascular volume is not enough to restore adequate blood pressure, and the use of inotropic agents may be required.33 Blood losses less than 10% of blood volume in a patient with normal PCV and TP values can be corrected with isotonic crystalloid replacement at a rate of three times the estimated blood loss amount.34,35 Isotonic crystalloid fluids equilibrate with the extravascular fluid compartments so that only 20% of the crystalloid administered remains in the intravascular space 2 hours after infusion.34,35 An acute blood loss of 10% of the blood volume in awake dogs with a normal PCV value produces no significant effect on oxygen delivery.36 Transfusions of whole blood (empirically, 20 to 25 ml/kg for dogs, 10 ml/kg for cats) or packed RBCs (empirically, 15 to 20 ml/kg for dogs) have been recommended in awake patients when more than 25% of the blood volume has been lost.17,37 While patients are anesthetized, however, they are less tolerant of blood loss, and rapid losses in excess of 10% of blood volume (or a hematocrit value less than 27% to 33%) indicate the need for whole blood or packed RBC administration, especially if a patient becomes hemodynamically unstable.38 PCV, however, is not a reliable indicator of acute blood loss because the PCV of a patient with an acute loss of whole blood will not initially change despite a loss in total blood volume and RBC content.39,40 In surgical procedures that carry a risk of blood loss, or in patients with a coagulopathy, blood should be typed and a patient’s blood volume (90 ml/kg for dogs, 60 ml/kg for cats) and maximum tolerated blood loss (10% to 20% of blood volume) calculated preoperatively. Intraoperative blood loss is monitored by counting blood-saturated cotton-tipped applicators or surgical sponges and by measuring the amount of blood aspirated from the surgical field. To calculate the blood loss from blood-soaked gauze sponges and laparotomy sponges, their weight can be compared with their dry weight, with 1 g of weight being approximately equal to 1 ml of blood.41 Alternatively, the following rule of

Table 1. Guide to Perioperative Fluid Therapy in Surgical Patients Fluid Therapy Recommendations

Fluid Therapy Considerations

Pediatric Patients (e.g., surgery for patent ductus arteriosus or persistent right aortic arch) Compared with adults, pediatric patients cannot Avoid overhydration of pediatric patients, administer fluids accommodate volume overload as efficiently and are more at 3–6 ml/kg/hr during surgery, prewarm fluids, and add susceptible to hypothermia and hypoglycemia. dextrose to fluids for longer procedures. Pediatric patients also have higher maintenance fluid requirements because of a high ratio of surface area to body weight.

Geriatric Patients Geriatric patients have a decreased cortical renal mass with decreased renal function and reserve as well as a diminished cardiac reserve. Geriatric patients are less tolerant than younger patients of dehydration or fluid overload.

Avoid overhydration, but maintain renal perfusion.

Cardiac Disease (e.g., mitral or tricuspid regurgitation, dilated cardiomyopathy, hypertrophic cardiomyopathy) Patients with cardiac disease are susceptible to intravascular Avoid large sodium loads; colloids are an alternative to fluid overload. crystalloids, but take care not to overexpand the intravascular compartment as it is more difficult to treat vascular overload from colloids than crystalloids; 0.9% saline is the commonly used solvent for colloids. Use reduced crystalloid fluid administration rates intraoperatively (3–6 ml/kg/hr); postoperatively, monitor for volume overload.

Renal Disease Maintenance of renal perfusion is important to prevent renal ischemia and anuric renal failure. Oliguria can be prerenal or renal in origin.

Diuresis (e.g., with mannitol solution) is recommended to minimize renal damage and shutdown. Use isotonic polyionic solution plus dopamine infusion in dogs (2–5 µg/kg/min) to maintain renal output. Use a slow bolus of mannitol solution over 20–30 min at 0.5 g/kg or CRI at 0.1 g/kg/hr (take care when patient is dehydrated). Furosemide may be administered at 1–2 mg/kg IV to promote diuresis (take care when dehydration and electrolyte changes exist). Be careful using low molecular weight synthetic colloids (especially dextran 40) because they can potentiate renal disease. Use an indwelling urinary catheter to monitor urinary output. In case of oliguria, use a fluid challenge initially with a crystalloid, and monitor urinary output, CVP, mean arterial pressure, and heart rate. If urinary output improves (>0.5 ml/kg/hr), prerenal oliguria is likely. If there is no response to fluid challenge, consider dopamine (for dogs only; for cats if hypotensive), with diuretic administration as above. Monitor for hypervolemia and overhydration.

Uroabdomen Urine in the peritoneal cavity leads to osmotically induced shifts in the fluid compartments. Because urine is hyperosmolar, water is drawn from the extracellular compartment, which results in hypovolemia. Serum electrolyte levels equilibrate with those in the peritoneal fluid, which results in hyperkalemia, hypovolemia, azotemia, and metabolic acidosis. Hyperkalemia, hypovolemia, and acidosis cause impaired cardiac function.

Stabilize the patient before anesthesia by abdominal lavage and fluid therapy to reduce hyperkalemia. See the box on p. 103 for treatment of hyperkalemia. Sodium bicarbonate (0.5–1 mEq/kg IV or 0.25–0.5 × kg × base excess [BE] × 0.3 mEq IV over 20–30 min) is used to treat significant acidosis and acute hyperkalemia.

High Gastrointestinal Obstruction (e.g., pyloric obstruction) Use of physiologic saline is indicated because of the Loss of gastric fluid of low pH can result in hypochloremic, acidifying effect and chloride concentration. hypokalemic metabolic alkalosis. Potassium supplementation is usually required.

Table 1 (continued) Fluid Therapy Recommendations

Fluid Therapy Considerations

Low Gastrointestinal Obstruction Loss of the duodenal reflux with a high bicarbonate concentration produces metabolic acidosis. Fluids, electrolytes, and plasma proteins are lost into the bowel lumen, and increased bowel wall permeability results in increased bacterial migration and absorption of toxins. Stagnation of intestinal contents results in bacterial overgrowth, villus irritation and edema, and malabsorption of water, electrolytes, and nutrients.

Balanced electrolyte solution is indicated to correct hypovolemia and acidosis and replace electrolyte deficits. Potassium supplementation of IV fluids may be required. Severe acidosis (pH <7.2) may require sodium bicarbonate administration (0.25–0.5 × kg × BE × 0.3 mEq over 20–30 min). Synthetic colloid therapy or plasma administration should be considered for hypoproteinemia (TP value <3.5 g/dl) or hypoalbuminemia (albumin value <2.0 g/dl).

Gastric Dilatation–Volvulus Impaired venous return, hypoperfusion, hypovolemia, endotoxic shock, systemic inflammatory response syndrome, and mixed acid–base status are common.

Shock doses of isotonic crystalloids and colloids, hypertonic saline, or hypertonic saline plus dextran are given to improve perfusion before anesthesia. Potassium supplementation may be indicated. Plasma plus heparin may be administered if disseminated intravascular coagulation exists; packed RBCs may be needed for excessive bleeding. Sodium bicarbonate may be required for acidemia (see above). Inotropic support and treatment of dysrhythmias are important, if indicated, to optimize cardiac output.

Septic Peritonitis Sepsis and systemic inflammatory response syndrome result in hypovolemia and increased vascular permeability. Patients are usually acidemic, hypokalemic, hyponatremic, and hypoglycemic.

Correct fluid and electrolyte imbalances with synthetic colloids and crystalloids; acid–base abnormalities usually return to normal when there is adequate volume expansion. Use potassium supplementation for hypokalemia. Use heparin and plasma therapy for disseminated intravascular coagulation. Add glucose to fluids for hypoglycemia. Inotropic support and treatment of dysrhythmias are important, if indicated, to optimize cardiac output.

Liver Disease

(e.g., liver mass, celiotomy for liver biopsy, portosystemic shunts) With liver failure, avoid fluids containing lactate because Use fluids with acetate or gluconate as bicarbonate precursors. the liver is responsible for metabolizing lactate. Synthetic colloid therapy may be required for low oncotic Coagulopathy, hypoproteinemia, hypoalbuminemia, pressure; fresh or fresh-frozen plasma may be needed to replace hypoglycemia, and sepsis may be present. coagulation factors and albumin. Use dextrose supplementation for hypoglycemia. Avoid overhydration with crystalloids in immature patients with portosystemic shunts.

Pancreatitis Acute generalized inflammation exists with the release of vasoactive substances and myocardial-depressant factors, absorption of toxins, and accumulation of large amounts of fluid within the peripancreatic tissues and peritoneal cavity. Further loss of fluids occurs with vomiting and sequestration caused by ileus, which results in hypovolemic shock. Intravascular fluid loss similar to extracellular fluid loss; electrolyte levels may be normal, but potassium levels may be low because of renal reabsorption of sodium in response to hypovolemia. Metabolic acidosis usually exists, resulting from shock.

Correct hypovolemic shock: Improve pancreatic microcirculation with isotonic crystalloids and synthetic colloids. Use fresh-frozen plasma transfusions to replace coagulation factors and α-macroglobulin. Take care not to exacerbate pulmonary edema with crystalloids because disruption of alveolar capillary membranes with vasoactive substances is often present. Additional potassium may be required after rehydration.

Brain Surgery or Cerebral Trauma Avoid cerebral edema.

Avoid overzealous isotonic crystalloid administration; supplement with synthetic colloids; 0.9% saline is the fluid of choice. Administer mannitol (1 g/kg IV, take care with dehydration) and furosemide (1 mg/kg IV, take care if dehydration and electrolyte changes exist) as needed to treat increased intracranial pressure. Avoid glucose-containing fluids unless hypoglycemia exists.

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thumb has been suggested: blood-soaked gauze sponges (4 × 4 inches) contain 5 to 10 ml of blood, whereas laparotomy sponges (12 × 12 inches [30 cm2]) moistened with physiologic saline absorb approximately 50 ml of blood.41 The amount of blood lost in aspirated fluids can be estimated from the following equation: Amount of = PCV of fluid × Volume of fluid blood lost PCV of patient Synthetic colloids or plasma is added to the fluid therapy regimen in patients with severe hypoproteinemia (TP value <3.5 g/dl or albumin value <2.0 g/dl) or when hypotension is refractory to treatment with crystalloid fluid boluses.25 Synthetic colloids can also be used to replace intraoperative blood loss, when administration of RBCs is not required and the coagulation status is normal. The fluid therapy requirements in specific diseases requiring surgery are given in Table 1.

POSTOPERATIVE FLUID THERAPY Fluid therapy is continued in the postoperative period to correct any remaining deficits, provide maintenance requirements, and replace ongoing losses. This therapy is especially important in critically ill patients. Remaining fluid deficits can be estimated on the basis of a patient’s physical and laboratory parameters after surgery. Consideration of a patient’s preoperative hydration status and the amount of fluid given pre- and intraoperatively can also guide postoperative fluid administration rates. A patient’s interstitial fluid deficit is calculated as follows: Milliliters required for replacement = % Dehydration × Body weight (kg) × 1,000 Percentage of dehydration is a clinical assessment based on physical parameters and supported by blood assays (i.e., PCV, TP, blood urea nitrogen, creatinine, pH, lactate) and urinalysis (specific gravity of urine; see Monitoring Fluid Therapy, p. 109). Maintenance fluid requirements can be calculated from the body weight in kilograms according to the following equations42 and are in the range of 30 to 75 ml/kg/day:

•

Dogs: Maintenance fluid requirement per day (ml) = 132 × Body weight (kg)0.75

•

Cats: Maintenance fluid requirement per day (ml) = 80 × Body weight (kg)0.75

•

Animals heavier than 2 kg: Maintenance fluid requirement per day (ml) = 30 × Body weight (kg) + 70

Abnormal ongoing fluid losses include those from vomiting, diarrhea, diuresis, transudation into a body cavity or the tissues, or burn wounds. Third spacing refers to abnormal accumulation of fluid in extracellular locations, such as the interstitial fluid space, thoracic and peritoneal cavities, and around traumatized tissue. These losses can be difficult to quantify but must be considered when fluid replacement needs are calculated because third spacing may lead to hypovolemia, dehydration, hypoproteinemia, and poor tissue perfusion. The rate of fluid administration to the postoperative patient is adjusted according to urinary output, body weight changes, and physical examination parameters. The calculated daily fluid requirement can be administered over 24 hours unless the patient needs a more rapid fluid rate to maintain perfusion and urinary output. When synthetic colloid therapy is indicated, such as for systemic inflammatory response syndrome or hypoproteinemia, CRI administered to maintain the colloid osmotic pressure above 14 mm Hg; the recommended synthetic colloid dosage is 0.4 to 0.8 ml/kg/hr IV for dogs and 0.2 to 0.4 ml/kg/hr IV for cats. 43 We administer CRI hetastarch at 1.0 to 2.0 ml/kg/hr IV in dogs and 0.5 to 1.0 ml/kg/hr IV in cats. High molecular weight colloid molecules reduce intravascular fluid loss and resulting interstitial edema. Synthetic colloid therapy is contraindicated in patients with severe coagulopathy and should be used cautiously in patients with renal failure, congestive heart failure, or pulmonary edema. When plasma albumin levels fall below 2.0 g/dl or coagulopathy is suspected, a fresh or fresh-frozen plasma transfusion is recommended at 10 ml/kg IV given over 4 to 6 hours.25

METHODS OF FLUID ADMINISTRATION Perioperative fluids are usually given via an intravenous catheter to a peripheral vein, usually cephalic or saphenous. A central venous catheter is recommended in critically ill patients to enable measurement of CVP. The central venous catheter is also recommended for administering fluids with osmolality values above 500 to 700 mOsm/L to avoid thrombophlebitis. Fluid administration sets are commonly used, and the number of drops to be administered per minute is calculated by the following formula: Drops per = Desired fluid rate (ml/hr) × drops/ml minute 60 min/hr The number of drops per milliliter varies according to the administration set, with larger sets having 10 to 15 drops/ml and pediatric administration sets having 60

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systemic vascular resistance.17 CVP can be misleading for assessing optimal right ventricular preload, especially in patients with altered ventricular comParameter Target pliance or intrathoracic disease.44 Colloid osmotic pressure 14–20 mm Hg PCV and TP are used to assess the CVP 6–8 cm H20 (4–6 mm Hg) need for blood products, although Mean arterial pressure >60 mm Hg, ideally >80 mm Hg there is a poor correlation between TP Systolic blood pressure >90 mm Hg and plasma oncotic pressure in hospiUrinary output >1–2 ml/kg/hr talized patients.45 A period of several Heart rate 80–120 bpm in dogs, 160–200 bpm in cats to 24 hours is required after hemorPlasma albumin >2.0 g/dl rhage for the PCV to decrease because transcapillary refill and renal conserTP >3.5 g/dl vation of sodium and water increase PCV >25% to 30% plasma volume.40 Administering crysBase deficit +4 to −4 mmol/L dogs, +4 to −7 mmol/L cats talloid fluids causes further hemodilu<2 mmol/L Lactate tion and may give the false impression that there is ongoing blood loss.46 Blood urea nitrogen and creatinine levels, in condrops/ml. Fluid administration pumps, although an junction with urine specific gravity, can be used to expensive initial investment, allow a more precise fluid assess prerenal azotemia. Urinary output is valuable for administration rate when an accurate delivery is critical. monitoring renal function and the adequacy of fluid This is especially important in pediatric and small administration. Electrolyte monitoring is important patients, patients with oliguric renal failure or cardiac disbecause electrolyte imbalances are common in critically ease, and geriatric patients. Administering perioperative ill patients and can have detrimental effects on cardiofluids SC or intraperitoneally is unreliable because vascular function.1–3 An arterial blood gas measurement peripheral and splanchnic vasoconstriction limits fluid indicates whether an acid–base imbalance is present absorption. The intraosseous route is an alternative for and provides information about ventilation and oxypuppies, kittens, cats, and small dogs when peripheral genation, which are important regulators of blood oxycatheterization is difficult. gen content and therefore oxygen delivery. Periodic blood glucose estimations are important in patients susMONITORING FLUID THERAPY ceptible to hypoglycemia or those requiring dextrose Monitoring fluid therapy is important to ensure adesupplementation. quate fluid replacement and oxygen delivery, prevent Colloid osmometry can be used for accurately assessoverhydration or hypervolemia, and ensure administraing plasma oncotic pressure subsequent to administertion of the appropriate fluid. There is no routine means ing synthetic colloids, whereas refractometric readings of measuring oxygen delivery in veterinary patients, of total solids are unreliable in animals receiving synand other subjective and objective parameters must be thetic colloid therapy.47,48 used to monitor the effectiveness of fluid therapy. Suggested target values for parameters used to assess perioperative fluid therapy are given in Table 2. REFERENCES Serial body weight measurements and physical exam1. Bahler RC, Rakita L: Cardiovascular function in potassiumdepleted dogs. Am Heart J 81(5):650–657, 1971. ination parameters, such as mental status, skin turgor, 2. Cohen HC, Gozo Jr EG, Pick A: The nature and type of pulse quality, capillary refill time, moistness of mucous arrhythmias in acute experimental hyperkalemia in the intact membranes, and temperature of the extremities, are dog. Am Heart J 82(6):777–785, 1971. important indicators of hydration status and perfusion. 3. Olinger GN, Hottenrott C, Mulder DG, et al: Acute clinical Periodic auscultation of the lungs and observation of an hypocalcemic myocardial depression during rapid blood transfusion and postoperative hemodialysis: A preventable complicaanimal’s respiratory rate and effort are important for tion. J Thorac Cardiovasc Surg 72(4):503–511, 1976. detecting fluid overload and pulmonary edema. 4. Moon PF: Fluid therapy and blood transfusion, in Seymour C, Although cardiovascular measures (e.g., arterial blood Gleed R (eds): BSAVA Manual of Small Animal Anaesthesia and pressure, CVP, heart rate) are generally useful for moniAnalgesia. Cheltenham, UK, BSAVA, 1999, pp 119–137. toring fluid therapy, they can be misleading. Arterial 5. Bailey JE, Pablo LS: Practical approach to acid–base disorders. Vet Clin North Am Small Anim Pract 28(3):645–662, 1998. blood pressure and heart rate can be unreliable indica6. Dhupa N, Proulx J: Hypocalcemia and hypomagnesemia. tors of cardiac output because of concurrent changes in Table 2. Suggested Target Values for Parameters Used to Assess Perioperative Fluid Therapy

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Vet Clin North Am Small Anim Pract 28(3):587–608, 1998. 7. DiBartola SP, de Morais AH: Disorders of potassium: Hypokalemia and hyperkalemia, in DiBartola SP (ed): Fluid Therapy in Small Animal Practice. Philadelphia, WB Saunders, 2000, pp 83–107. 8. Rosol TJ, Chew DJ, Nagode LA, et al: Disorders of calcium. Hypercalcemia and hypocalcemia, in DiBartola SP (ed): Fluid Therapy in Small Animal Practice. Philadelphia, WB Saunders, 2000, pp 108–162. 9. Schaer M: Disorders of serum potassium, sodium, magnesium and chloride. J Vet Emerg Crit Care 9(4):209–217, 1999. 10. Klide AM: Cardiovascular effects of enflurane and isoflurane in the dog. Am J Vet Res 37(2):127–131, 1976. 11. Ko JCH, Golder FJ, Mandsager RE, et al: Anesthetic and cardiorespiratory effects of a 1:1 mixture of propofol and thiopental sodium in dogs. JAVMA 215(9):1292–1296, 1999. 12. Maier RV, Bulger EM: Endothelial changes after shock and injury. New Horizons 4(2):211–223, 1996. 13. Rudloff E, Kirby R: Colloids: Current recommendations, in Bonagura JD (ed): Kirk’s Current Veterinary Therapy XIII—Small Animal Practice. Philadelphia, WB Saunders, 2000, pp 131–136. 14. Mandell DC, King LC: Fluid therapy in shock. Vet Clin North Am Small Anim Pract 28(3):623–644, 1998. 15. Smiley LE, Garvey MS: The use of hetastarch as adjunct therapy in 26 dogs with hypoalbuminemia: A phase two clinical trial. J Vet Intern Med 8(3):195–202, 1994. 16. Holcroft JW, Trunkey DD, Carpenter MA: Extravasation of albumin in tissues of normal and septic baboons and sheep. J Surg Res 26(4):341–347, 1979. 17. Kudnig ST, Mama K: Perioperative fluid therapy. JAVMA 221(8):1112–1121, 2002. 18. Duval D: Use of hypertonic saline solutions in hypovolemic shock. Compend Contin Educ Pract Vet 17(10):1228–1231, 1995. 19. Schertel ER, Allen DA, Muir WW, et al: Evaluation of a hypertonic saline-dextran solution for dogs with shock induced by gastric dilatation-volvulus. JAVMA 210(2):226–230, 1997. 20. Schertel ER, Allen DA, Muir WW, et al: Evaluation of a hypertonic sodium chloride/dextran solution for treatment of traumatic shock in dogs. JAVMA 208(3):366–370, 1996. 21. Rudloff E, Kirby R: Fluid therapy: Crystalloids and colloids. Vet Clin North Am Small Anim Pract 28(2):297–328, 1998. 22. Allen DA, Schertel ER, Muir WW, et al: Hypertonic saline/dextran resuscitation of dogs with experimentally induced gastric dilatation-volvulus shock. Am J Vet Res 52(1):92–96, 1991. 23. Prough DS, Whitley JM, Taylor CL, et al: Small-volume resuscitation from hemorrhagic shock in dogs: Effects of systemic hemodynamics and systemic blood flow. Crit Care Med 19(3):365–372, 1991. 24. Kien ND, Kramer GC, White DA: Acute hypotension caused by rapid hypertonic saline infusion in anesthetized dogs. Anesth Analg 73(5):597–602, 1991. 25. Kirby R: Transfusion therapy in emergency and critical care medicine. Vet Clin North Am Small Anim Pract 25(6):1365– 1386, 1995. 26. Standl T, Horn P, Wilhelm S, et al: Bovine haemoglobin is more potent than autologous red blood cells in restoring muscular tissue oxygenation after profound isovolaemic haemodilution in dogs. Can J Anaesth 43(7):714–723, 1997. 27. Chan DL, Freeman LM, Rozanski EA, et al: Colloid osmotic pressure of parenteral nutrition components and intravenous fluids. J Vet Emerg Crit Care 11(4):269–273, 2001. 28. Gaynor JS, Wertz EM, Kesel LM, et al: Effect of intravenous

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administration of fluids on packed cell volume, blood pressure, and total protein and blood glucose concentrations in healthy halothane-anesthetized dogs. JAVMA 208(12):2013–2015, 1996. Lobetti R, Lambrechts N: Effects of general anesthesia and surgery on renal function in healthy dogs. Am J Vet Res 61(2):121–124, 2000. Yogendran S, Asokumar B, Cheng DCH, et al: A prospective randomized double-blinded study of the effect of intravenous fluid therapy on adverse outcomes on outpatient surgery. Anesth Analg 80(4):682–686, 1995. Campbell IT, Baxter JN, Tweedie IE, et al: IV fluids during surgery. Br J Anaesth 65(5):726–729, 1990. Lowell JA, Schifferdecker C, Driscoll DF, et al: Postoperative fluid overload: Not a benign problem. Crit Care Med 18(7):728–733, 1990. Mazzaferro E, Wagner AE: Hypotension during anesthesia in dogs and cats: Recognition and treatment. Compend Contin Educ Pract Vet 23(8):728–737, 2001. Vaupshas HJ, Levy M: Distribution of saline following acute volume loading: Postural effects. Clin Invest Med 13(4):165–177, 1990. Carey JS, Scharschmidt BF, Culliford AT, et al: Hemodynamic effectiveness of colloid and electrolyte solutions for replacement of simulated operative blood loss. Surg Gynecol Obstet 131(4):679–686, 1970. Sarelius IH, Sinclair JD: Effects of small changes of blood volume on oxygen delivery and tissue oxygenation. Am J Physiol 240(9):H177–H184, 1981. Wagner BK, D’Amelio LF: Pharmacologic and clinical considerations in selecting crystalloid, colloidal, and oxygen-carrying resuscitation fluids, part 1. Clin Pharm 12(5):335–346, 1993. Czer LS, Shoemaker WC: Optimal hematrocrit value in critically ill post-operative patients. Surg Gynecol Obstet 147(3):363–368, 1978. Cordts PR, LaMorte WW, Fisher JB, et al: Poor predictive value of hematocrit and hemodynamic parameters for erythrocyte deficits after extensive vascular operations. Surg Gynecol Obstet 175(3):243–248, 1992. Skillman JJ, Awwad HK, Moore FD: Plasma protein kinetics of the early transcapillary refill after hemorrhage in man. Surg Gynecol Obstet 125(5):983–996, 1967. Wagner AE, Dunlop CI: Anesthetic and medical management of acute hemorrhage during surgery. JAVMA 203(1):40–45, 1993. Haskins SC: A simple fluid therapy planning guide. Semin Vet Med Surg 3(3):227–236, 1988. Mathews KA: The various types of parenteral fluids and their indications. Vet Clin North Am Small Anim Pract 28(3):483–513, 1998. Shoemaker WC, Parsa MH: Invasive and noninvasive physiologic monitoring, in Shoemaker WC, Ayres SM, Grenvik A, et al (eds): Textbook of Critical Care, ed 3. Philadelphia, WB Saunders, 1995, pp 252–266. Brown SA, Dusza K, Boehmer J: Comparison of measured and calculated values for colloid osmotic pressure in hospitalized animals. Am J Vet Res 55(7):910–915, 1994. Stamler KD: Effect of crystalloid infusion on hematocrit in nonbleeding patients, with applications to clinical traumatology. Ann Emerg Med 18(9):747–749, 1989. Bisera J, Weil MH, Michaels S, et al: An “oncometer” for clinical measurement of colloid osmotic pressure of plasma. Clin Chem 24(9):1586–1589, 1978. Bumpus SE, Haskins SC, Kass PH: Effect of synthetic colloids on refractometric readings of total solids. J Vet Emerg Crit Care 8(1):21–26, 1998.

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Compendium February 2003

Perioperative Fluid Therapy 111

ARTICLE #2 CE TEST The article you have read qualifies for 1.5 contact hours of Continuing Education Credit from the Auburn University College of Veterinary Medicine. Choose the best answer to each of the following questions; then mark your answers on the postage-paid envelope inserted in Compendium.

CE

1. Synthetic colloids should be considered part of the fluid therapy regimen when a. a hypotensive patient does not respond to crystalloid bolus injections. b. coagulopathy is present. c. sepsis is present. d. renal failure is present. e. a and c 2. Hypertonic saline can be administered a. as fast as possible. b. in patients with severe hypovolemic shock. c. by any route. d. without any additional fluid therapy. e. to achieve a longer duration of intravascular expansion than that possible with colloids. 3. Acute blood loss in a patient with normal PCV and TP values should initially be treated with a. isotonic crystalloids at three times the volume of blood loss. b. hypertonic saline. c. a plasma transfusion. d. whole blood. e. packed RBCs. 4. Fluid therapy should be continued postoperatively a. to prevent postoperative oliguria. b. to correct ongoing fluid losses. c. on the basis of any remaining deficits and maintenance requirements. d. to help prevent third spacing secondary to low colloid osmotic pressure. e. all of the above 5. Select the incorrect answer: After an acute hemorrhage, a. the PCV will fall abruptly in proportion to the amount of blood lost. b. the PCV will not change for several hours to 24 hours.

c. heart rate and mean arterial blood pressure are more sensitive indicators of blood loss than is PCV. d. whole blood should be administered on the basis of the volume of blood lost rather than the PCV. e. administration of isotonic crystalloids can give a false impression of ongoing blood loss caused by hemodilution. 6. Metabolic changes that can occur with uroabdomen include a. hypokalemia, metabolic acidosis, and azotemia. b. hyperkalemia, metabolic acidosis, and azotemia. c. hypokalemia and metabolic alkalosis. d. hyperkalemia, metabolic alkalosis, and azotemia. e. hyperkalemia and metabolic alkalosis. 7. The IV fluid that should be avoided in the presence of liver failure is a. lactated Ringer’s solution (Abbott Laboratories). b. Normosol-R (Abbott Laboratories). c. hetastarch. d. Oxypolygelatin (DMS Laboratories). e. Ringer’s solution (Abbott Laboratories). 8. For a 20-kg dog receiving IV fluids intraoperatively at 10 ml/kg/hr via a 10 drop/ml dripset, ____________ drops/min should be administered. a. 1.7 c. 33 e. 10 b. 3.3 d. 200 9. Which statement regarding fluid therapy requirements with gastric dilatation–volvulus is false? a. Acute systemic inflammatory response syndrome is common and causes decreased duration of intravascular volume expansion when crystalloids are used. b. Colloids are often required because of the presence of systemic inflammatory response syndrome and hypoproteinemia. c. Bicarbonate supplementation is recommended to correct severe metabolic acidosis. d. Fresh-frozen plasma administration is recommended to treat coagulopathy associated with disseminated intravascular coagulation. e. Potassium supplementation of IV fluids is rarely required. 10. The maintenance fluid requirement for a 5-kg cat is _____ ml/hr. a. 100 c. 9 e. 20 b. 220 d. 2

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