Perioperative Fluid Administration

Perioperative Fluid Administration


Perioperative fluid therapy is a vital adjunct to any anesthetic plan. The term perioperative is defined as the period of time extending from when the animal goes into the hospital, clinic, or veterinarian’s office for surgery until the time the animal is discharged home. Almost all drugs used to produce anesthesia decrease the force of cardiac contraction and cause vasodilatation thereby increasing intravascular volume and resulting in relative hypovolemia. These effects generally lead to decreased cardiac output (blood flow) and arterial blood pressure (BP). It is important to remember that intravenous (IV) fluids are drugs and that their administration during anesthesia helps maintain an adequate and effective circulating blood volume, improve cardiac output, and enhance tissue perfusion. Additionally, perioperative fluid therapy is frequently administered to treat electrolyte and acid-base disorders. The choices for acute fluid therapy frequently include balanced electrolyte solutions (crystalloids), colloids, plasma, cell-free blood substitutes, and blood.

General Considerations (Table 16-1)

Anesthesia, surgery, and many of the diseases for which surgical intervention is required disturb cardiac function, smooth muscle vascular tone, blood flow distribution, plasma electrolyte concentrations and acid-base balance potentially altering the effective circulating blood volume (the volume circulating).

Many diseases produce changes in the relative or absolute blood volume, electrolyte concentrations, and acid-base balance (Table 16-2)

Common side effects of anesthesia

Imbalances associated with or caused by surgery

II Fluid loss leads to a decrease in the “effective” circulating blood volume eventually resulting in a decrease in cardiac output, a redistribution of blood to vital organs (heart, brain, lung), and the development of metabolic acidosis

III Fluid administration in young or small animals (<3 kg) should be supplemented with a source of calories (dextrose) and monitored closely to prevent hypothermia and/or overhydration

IV The administration of large quantities of room-temperature fluids to any animal can produce hypothermia and hemodilution, resulting in coagulation abnormalities

Normal Body Water Distribution (Fig. 16-1)

Total body water represents 55% to 75% of body weight (use 60%), primarily depending on the animal’s age and percentage of body fat

II Extracellular water (ECW): the water outside cells and constituting the blood (plasma; red blood cells [RBCs]) volume and interstitial fluid volume. ECW ranges from 23% to 33% of body weight (use 30%); the percentage is greater in very young animals

III Interstitial water constitutes 15% to 25% of body weight

IV Plasma water constitutes approximately 5% of body weight

Extracellular water equals plasma water plus interstitial water

VI Intracellular water constitutes 35% to 45% of body weight

VII Blood volume constitutes 8% to 10% of body weight (approximately 90 mL/kg of body weight), depending on the hematocrit; hematocrit measures how much space in the blood is occupied by RBCs and is also referred to as the packed red cell volume or packed cell volume (PCV) and abbreviated as Hct or Crit

Electrolyte Distribution

Extracellular water contains large quantities of salt: sodium and chloride ions. The extracellular fluids (plasma and interstitial fluid) also contain smaller quantities of other solutes

II Intracellular water contains large quantities of potassium ions

Principles of Fluid Administration

Correct dehydration and electrolyte and acid-base imbalances 12 to 24 hours before anesthesia when possible

II Do not attempt to replace dehydration or chronic fluid losses acutely; severe dilution of plasma proteins, RBCs, and electrolytes may be produced (see Table 16-2)

Normal daily fluid maintenance rates vary as follows:

Calculation of replacement fluid volume in dehydrated animals

1. Body weight (kg) × % dehydration (figured as a decimal) = fluid deficit (L) (e.g., 20 kg × 10% dehydration = 2 L fluid deficit); reassess periodically to determine the response to volume administered

2. Fluid administration to correct dehydration should be administered over a 6- to 12-hour period or added to the maintenance fluid volume and administered over a 24-hour period

III Monitor hemodynamics, pulmonary, and renal function when administering fluids rapidly

Cardiac function

1. Monitor arterial BP; systolic BP >90 mm Hg; mean BP >60 mm Hg

2. Auscultate the chest; if the total protein (TP) drops below 3.5 g/dL from fluid administration, pulmonary edema may occur

3. Central venous pressure (0.5 to 5.0 cm H2O) or pulmonary capillary wedge pressure (5 to 10 mm Hg) can be monitored, although their predictive value for determining rates and volumes of fluid administration is low unless fluids are administered in excess or the animal develops right heart failure

4. Measures of systolic arterial pressure variation (SPV) or pulse–oximeter-derived plethysmographic variability index (PVI) provides valuable information regarding fluid requirements and the effectiveness of fluid administration (see: Chapter 14)

Renal function

Pulmonary function—overhydration can lead to pulmonary edema initially exemplified by increases in respiratory rate, increased breathing effort (abdominal contraction) and increased lung (bronchovesicular) sounds (Box 16-1).

Fluid Administration During Anesthesia (Table 16-3; Boxes 16-2 and 16-3)

Sep 6, 2016 | Posted by in SUGERY, ORTHOPEDICS & ANESTHESIA | Comments Off on Perioperative Fluid Administration

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