Fluid and electrolyte and acid base balance. The body fluids are organized into functional compartments that are dynamic but ordered. The volume and composition of these compartments must be maintained in order for normal physiologic and biochemical actions to occur. Electrolytes dissolved in body fluids play a critical function in almost all living activities. Electrolyte transmembrane motions are important for the electrical events that arise in nerve conduction and muscular contraction, as well as serving as crucial cofactors in many metabolic activities mediated by enzymes.
The pH of bodily fluids is kept within specific ranges. This is required for protein structure and function to be maintained, which is a prerequisite for the normal course of metabolic events. Almost every organ system is involved in maintaining fluid equilibrium and/or is negatively affected by imbalances. A state of disturbed fluid and electrolyte balance occurs in many illness states as a result of impaired fluid intake, excessive fluid losses, or organ injury and malfunction.
When the body’s water balance is disrupted, more fluid is lost than is absorbed, resulting in a decrease in circulating blood volume and tissue dehydration. Rapid consumption of huge amounts of water, on the other hand, might contribute to dehydration (water intoxication).
Loss of electrolytes, shifts in individual electrolytes, or relative changes in concentrations induced by water loss are all typical causes of electrolyte imbalances. Hyponatremia, hypokalemia, hyperkalemia, hypocalcemia, hypochloremia, and hypophosphatemia are all common electrolyte abnormalities.
Acid-base imbalances, either acidemia or alkalemia, result from the addition of acid and depletion of alkali reserve, or the loss of acid and an increase in alkali reserve proportional to the input of acid.
Hypoalbuminemia or hypoproteinemia comes from severe gastrointestinal disease, renal glomerular disease, peritonitis, pleuritis, extensive burns, hepatic failure, chronic malnutrition, and severe hunger, and is caused by hypoalbuminemia or hypoproteinemia (increased loss of plasma protein, decreased production of plasma protein, or third spacing of plasma protein). Generalized edema is the most common clinical indication of low oncotic pressure.
Normal Values
- Sodium (Na+) 135-145 mEq/L
- Potassium (K+) 3.5-.50 mEq/L
- Calcium (Ca++) 8-10 mg/dL
- Magnesium (Mg++) 1.8-2.4 mg/dL
- Phosphorous (PO4) 2.5-4.5 mg/dL
- Creatinine (Cr) 0-1 mg/dL
- Blood urea nitrogen 10-30 ug/dL
- Ph 7.35-7.45
- PaCO2 35-45 mmHg
- PO2 >80 mmHg
- HCO3 22-26 mmHg
- SaO2 90-100 %
- Red blood cells (RBC) Males 4.6-6.2 mil/mm3
- Red blood cells (RBC) Females 4.2-5.4 mil/mm3
- White blood cells (WBC) 4800-10,800 mm3
- Hemoglobin (Hgb) Males 13-18 g/dL
- Hemoglobin (Hgb) Females 12-16 g/dL
- Hematocrit (Hct) Males 42-52%
- Hematocrit (Hct) Females 37-48%
- Glycosolated Hemoglobin (Hgb A1C) 5% (up to 7% in diabetic)
- Erythrocyte Sedimentation Rate (ESR)
Electrolyte Imbalances
The majority of electrolyte imbalances are caused by a net loss of electrolytes linked with gastrointestinal disorders. Electrolyte losses are also caused by sweating, excessive salivation and vomiting, and exudation from burns, but these are negligible in agricultural animals, with the exception of sweating in horses and dysphagia in ruminants. Sodium, chloride, potassium, calcium, phosphorus, and magnesium are the electrolytes to be concerned about. Bicarbonate losses are discussed later.
Hyponatremia
Sodium is the most abundant ion in extracellular fluid and is primarily responsible for maintaining the extracellular fluid’s osmotic pressure. Increased sodium loss through the intestinal tract is the most common cause of hyponatremia in enteropathies. This is most noticeable in horses suffering from severe diarrhea, and to a lesser extent in calves suffering from acute diarrhea. The extracellular fluid suffers as a result of salt loss.
Hyponatremia produces an increase in renal water excretion in an attempt to maintain normal osmotic pressure, resulting in a decrease in extracellular fluid space, which leads to a reduction in circulating blood volume, hypotension, peripheral circulatory failure, and eventually renal failure. Muscle wasting, hypothermia, and severe dehydration are all common symptoms.
Isotonic dehydration occurs when sodium and water are lost at the same time. Hypertonic dehydration occurs when there is a loss or deprivation of water along with small sodium losses or deprivation. Animals that are unable to drink the water due to an esophageal obstruction can develop hypertonic dehydration.
Hypernatremia
Water restriction or mixing errors in newborn animals are the most common causes of hypernatremia, especially in milk-replacer solutions or oral electrolyte formulations given to neonatal calves with diarrhea as part of dehydration management. Because milk-replacer formulations are increasingly reliant on whey from cheese production, which has a high sodium content, hypernatremia appears to be on the rise in dairy calves given milk replacer in North America.
High-salinity water is a less prevalent cause of hypernatremia. 2 After receiving hypertonic saline (7.2 percent NaCl), hypernatremia occurs briefly, but serum sodium concentrations never reach 170 mEq/L and may infrequently exceed 160 mEq/L for a few minutes. The clinical effects of transient episodes of mild hypernatremia caused by intravenous hypertonic saline injection are unknown.
Hypochloremia
In acute intestinal obstruction, dilatation and impaction, volvulus of the abomasum, and enteritis, hypochloremia occurs as a result of an increase in the net loss of the electrolyte in the digestive tract (Fig. 5-7 ). Mucosal cells secrete a considerable amount of chloride in the abomasum in exchange for bicarbonate, which goes into the plasma. Gastric juice contains hydrogen, chloride, and potassium ions, which are generally absorbed by the small intestine. Obstruction of the proximal section of the small intestine and failure of abomasal emptying result in the sequestration of substantial amounts of chloride, hydrogen, and potassium ions, resulting in a hypochloremic hypokalemic metabolic alkalosis.
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