Fluids, Electrolytes, and Acid-Base Balance

Fluids, Electrolytes, and Acid-Base Balance

• Fluids are water with dissolved or suspended substances (glucose, proteins, ions, cells).
• Electrolytes are mineral salts that dissolve in water and separate into ions (charged particles). Cations include sodium, potassium, calcium, and magnesium. Anions include chloride, bicarbonate, and phosphate.
• Fluid distribution in the body includes: 65% intracellular (inside cells), 35% extracellular (outside cells); 25% interstitial (between cells), 8% intravascular (in blood vessels), and 2% transcellular (in small fluid pockets).
• Homeostasis is maintained through diffusion (high to low), osmosis (low to high), filtration (high to low), and active transport (low to high using ATP).
• Edema results from an error in filtration.
• Factors affecting intake and absorption include fluid intake (food, G-tube), thirst triggered by hypovolemia, increased blood osmolality, or decreased blood volume. Fluid distribution includes filtration between spaces (kidneys, vascular/interstitial), and osmosis between cells. Fluid Output includes sensible losses (kidneys/urine, diarrhea, emesis) and insensible losses (lungs, skin).

The Renin-Angiotensin-Aldosterone System (RAAS)

• The renin-angiotensin-aldosterone system (RAAS) increases blood volume and increases blood pressure.
• Renin is made by the liver, aldosterone is produced by the adrenal glands, ADH is made in the hypothalamus and released by the posterior pituitary, ANP is made by atrial cells in the heart, and renin is produced by the heart.
• Direct effects of RAAS include constricting arteries, increasing cardiac output, increasing blood pressure and volume, decreasing glomerular filtration rate, and increasing thirst.
• Aldosterone causes nephron distal tubules to reabsorb more sodium and water, increasing blood volume.
• Atrial natriuretic peptide (ANP) decreases blood volume and pressure by increasing the glomerular filtration rate, decreasing sodium reabsorption, and inhibiting renin, aldosterone, and ADH release.

Fluid Balance

• Signs and symptoms of fluid volume overload include weight gain, hypertension, tachycardia, bounding pulse, crackles, dyspnea, orthopnea, and pitting edema. Jugular vein distension is also observed.
• Signs and symptoms of fluid volume deficit include weight loss, hypotension (orthostatic first), tachycardia, tachypnea, poor/tenting turgor, dry cracked mucous membranes, and scant, dark urine (oliguria).

Fluid Balance in Children

• Children are at greater risk of dehydration than adults.
• Fluid and electrolyte imbalances occur more frequently and rapidly in pediatric patients, necessitating prompt management.
• Infants and young children have difficulties compensating for fluid losses. Insensible losses through skin increase with fever. A child loses approximately 7ml/kg every 24 hours for each degree above 99.

S/S of Dehydration in Children

• Mild dehydration presents with normal appearance, increased thirst, and decreased urine output (UOP).
• Moderate dehydration presents with tacky mucosa, decreased tears, decreased UOP, increased thirst, and slightly sunken orbits. Lethargy, poor turgor, tachycardia, and tachypnea are also observed.
• Severe dehydration presents with dry, cracked mucosa, absent tears, oliguria/anuria, intense thirst, sunken orbits, tenting turgor, tachycardia (>160), tachypnea, hypotension (<70), and cool and mottled skin.

Fluid Resuscitation in Children

• The goal is to maintain fluid and electrolyte balance.
• Oral hydration is preferred for alert children.
• The goal is 10ml/kg/hour plus losses from the previous hour. Parenteral routes are used for moderate to severe dehydration. 
• Administer 20ml/kg fluid boluses. 
• Use infusion pumps for precise intake and output measurement (I&O). 
• Treatment focuses on addressing the underlying cause of the fluid imbalance.

Fluid Balance in the Elderly

• Elderly individuals are at greater risk of fluid volume deficit due to decreased body water percentage, decreased thirst mechanism, difficulties obtaining fluids due to mobility issues, and potential medication-induced fluid excretion.

Electrolytes

• Electrolytes include sodium (135-145mEq/L), potassium (3.5-5mEq/L), calcium (8.4-10.5mg/dL), magnesium (1.5-2.5mEq/L), chloride (95-105mEq/L), bicarbonate (22-26 Arterial/24-30 Venous), and phosphate (2.7-4.5mg/dL).
• Hyponatremia (<136mEq/L) and hypernatremia (>145mEq/L) are electrolyte imbalances affecting sodium levels, each with different causes, symptoms, and critical findings.
• Hypokalemia (<3.5mEq/L) and hyperkalemia (>5mEq/L), related to potassium levels, involve a range of causes, symptoms, and critical findings
• Hypocalcemia (<9mg/dL) and hypercalcemia (>10.5mg/dL), related to calcium levels, present with a variety of causes, symptoms and critical findings.
• Hypophosphatemia (<3mg/dL) and hyperphosphatemia (>4.5mg/dL), related to phosphate levels, involve a range of causes, symptoms, and critical findings.
• Hypomagnesemia (<1.8mEq/L) and hypermagnesemia (>2.6mEq/L) include a range of causes, symptoms and critical findings for magnesium levels.
• ECG changes in hyperkalemia may include peaked T waves, prolonged QRS intervals, and wide QRS complexes.

Acid-Base Balance

• pH is the potential to accept more hydrogen. High pH represents alkalosis (base), and low pH represents acidosis.
• The body has two primary types of acids: carbonic acid (H2CO3) that is expelled during exhalation, and metabolic acids (lactic and citric acids) that are expelled through the kidneys.
• The bicarbonate buffer system regulates acid-base balance by absorbing or releasing hydrogen ions.
• Blood buffers (bicarbonate, phosphate, hemoglobin, and plasma proteins) act immediately to bind hydrogen ions.
• Respiration regulates carbon dioxide levels, impacting acid-base balance.
• Kidneys regulate bicarbonate and hydrogen excretion, a slower but more effective process
• Normal pH range is 7.35-7.45, with CO2 levels typically 35-45mmHg, and bicarbonate (HCO3) ranging from 22-26mEq/L.

Acid-Base Imbalances

• Causes and associated findings are provided for metabolic and respiratory acidosis and alkalosis in the patient presentations.