Fluid, Electrolyte, and Acid-Base Balance

• Module 2B discusses alterations of fluid, electrolyte, and acid-base balance
• The agenda includes fluid exchange and capillary dynamics, acid-base imbalances, electrolyte imbalances, and blood pressure regulation with alterations in fluid balance
• Focus Points and Reading Goals include the differences between metabolic/respiratory acidosis and alkalosis, how electrolyte imbalances affect the body, how fluid volume affects blood pressure, and how fluid moves

Body Fluids: Composition

• Body fluid compartments maintain electrochemical balance, where the number of negative charges equals positive charges
• Intracellular Fluid (ICF) is located within the cells
• Extracellular Fluid (ECF) is located outside the cells
• Transcellular fluid, known as the "third space," is located in CSF and various body spaces
• Electrolytes, which are electrically charged, make up 95% of solutes
• Cations are positively charged. Example: Na+
• Anions are negatively charged. Example: Cl-
• Water and electrolytes move across cell membranes by passive which requires no-energy or active mechanisms with energy

Intracellular Fluid

• Makes up approximately 40% of total body weight
• Regulated by proteins and organic compounds within body cells
• Cell membranes are mostly freely permeable to water
• Osmotic proteins and organic compounds are generally unable to pass through the membrane

Extracellular Fluid

• Makes up about 20% of total body weight
• Contains electrolytes, oxygen, glucose, and cellular waste products
• Divided into Vascular Fluid Compartments, Interstitial Fluid Compartments, and Transcellular Fluid Compartments

Distribution of Body Fluids

• Total body water consists of intracellular and extracellular fluid.
• With age, there will a be decreased percentage of total body water, increased adipose and decreased muscle mass, renal decline, and diminished thirst perception
• Pediatrics have 75%-80% of body weight as water and are susceptible to significant changes in body fluid

Membrane Transport Definitions

• Hydrostatic Pressure - the pushing force exerted by water in the bloodstream
• Osmotic Pressure - the pressure exerted by solutes in solution
• Oncotic Pressure - the force exerted by albumin in the bloodstream; it regulates the movement of fluids at the venous end of the capillary
• Osmolality evaluates the body's hydration status based on fluid and electrolytes in solution
• Osmolarity evaluates the number of particles or ions in a volume of fluid
• Tonicity is the amount of solutes in solution compared with the bloodstream

Movement Across the Cell Membrane

• The cell membrane acts as a barrier, controlling which substances enter and leave the cell, allowing in essential elements while keeping out harmful substances
• Most cell membranes are semi-permeable, allowing only certain substances to cross
• Extracellular fluid typically has higher concentrations of sodium, calcium, and chloride ions compared to intracellular fluid
• Intracellular fluid generally has higher concentrations of potassium compared to extracellular fluid.

Membrane Transport Mechanism

• Active Transport uses the Sodium-Potassium-ATPase pump
• Passive transport includes diffusion, filtration, osmosis, tonicity, and facilitated transport

Diffusion

• Diffusion is the process in which molecules passively spread from areas of high concentration to areas of low concentration
• It involves the movement of charged or uncharged particles along a concentration gradient
• Water and electrolytes diffuse from high concentrations to lower concentrations until equilibrium is reached

Osmosis

• Only water molecules move through a membrane down the concentration gradient
• Water moves from where it is more concentrated (fewer solutes) to where it is less concentrated (more solutes)
• Osmotic pressure is pressure generated as water moves across a membrane

Tonicity of IV Solutions

• Isotonic solutions are of the same tonicity as blood, such as normal saline (0.9%), and act as volume expanders
• Hypotonic solutions contain fewer particles and more water than blood, adding water to the blood and causing fluid to shift from ECF to ICF; used in dehydrated patients
• Hypertonic solutions contain more particles and less water than blood, causing fluids to shift from ICF to ECF and can cause body cells to shrink. Example: Mannitol, 3% NS

Hormones

• Intake and output regulates to prevent fluid volume overload (edema) and deficit (dehydration)
• Activation of the renin-angiotensin-aldosterone system (RAAS) helps the body attempts to reach homeostasis
• Natriuresis is the excretion of sodium and water by the kidney in response to excess ECF volume
• Atrial Natriuretic Peptide (ANP) and Brain Natriuretic Peptide (BNP) are natriuretic peptides.
• BNP is secreted in response to fluid volume overload stretching hear, and is often measured with cardiac presentation
• CNP is C-Type Natriuretic Peptide

Edema

• Localized vs. generalized edema, pitting edema, and dependent edema can be helped with a low sodium diet or diuretics.
• Edema is the accumulation of fluid within the interstitial spaces
• It can be caused by an increase in capillary hydrostatic pressure, a decrease in plasma oncotic pressure, increases in capillary permeability, or lymph obstruction (lymphedema)

Hypervolemia versus Hypovolemia

• Water Excess (Hypervolemia) causes include compulsive water drinking, decreased urine formation, syndrome of inappropriate ADH (SIADH), heart failure, weight gain
• SIADH includes ADH secretion in the absence of hypovolemia or hyperosmolality
• Water Deficit (Hypovolemia) can be caused by pure water deficits, dehydration, burns, fever, perspiration, or hypernatremia, which all can lead to elevated hematocrit and serum sodium

Electrolytes

• Electrolytes include sodium, potassium, calcium, and magnesium

Electrolytes: Sodium

• Sodium (Na+) is the primary ECF cation, regulating osmotic forces and water movement
• Normal value of sodium 135-145 mEq/L
• Hyponatremia is a characterized as serum sodium < 135 mEq/L, plasma hypo-osmolality, cellular swelling.
• It also includes Lethargy, confusion etc
• Hypernatremia is a characterized as serum sodium > 145 mEq/L and water movement from the ICF to the ECF.

Electrolytes: Potassium

• Potassium 3.5-5.2 mEq/dL regulates intracellular electrical neutrality in relation to Na+ and H+ and is essential for the heart.
• Hypokalemia is a potassium level <3.5 mEq/L, which can includes Membrane hyperpolarization that causes a decrease in neuromuscular excitability, skeletal muscle weakness, smooth muscle atony, and cardiac dysrhythmias
• Hyperkalemia is a level >5.2 mEq/L, caused by increased intake, shift of K+ from ICF into ECF, or decreased renal excretion. Watch patients with acute kidney injury

Electrolytes: Calcium

• Calcium 8.7-10.5 is located at 99% in the bone structure and teeth.
• Hypocalcemia is a calcium level < 8.7 mg/dL, inadequate intestinal absorption, decreased PTH and vitamin D. It causes Increased neuromuscular excitability and prolonged QT.
• Hypercalcemia is calcium level > 10.5 mg/dL, can happen due to hyperparathyroidism; metastases with calcium and can cause impaired renal function as well as kidney stones.
• Chvostek's sign includes Twitching of the lip to spasm of all facial muscles
• Trousseau's Sign includes Induction of carpopedal spasm by inflation of SBP for 3 minutes

Electrolytes: Magnesium

• Magnesium acts as a cofactor in intracellular enzymatic reactions, increases neuromuscular excitability, and has a normal value of 1.8 to 3.0 mEq/L
• Hypomagnesemia is a level < 1.8 mEq/L that increases muscular irritability
• Hypermagnesemia is a level > 3.0 mEq/L that comes with excessive loss of deep tendon reflexes

Acid-Base Balance

• Body maintains normal balance through regulating the PH
• An acid can release an H+
• Base and accept a H+
• Normal PH is 7.35 to 7.45
• Buffering system in the Lungs and kidneys help neutralize the H plus that is needed to be excreted

Buffering Systems

• A buffer is a chemical that can bind excessive H+ or OH- without a significant change in pH.
• The most important plasma buffering systems are the carbonic acid-bicarbonate pair, protein and ion exchange buffering.

Imbalances in the blood

• Normal arterial blood pH is 7.35 to 7.45
• Acidosis includes a systemic increase in H+ concentration or decrease in bicarbonate
• Alkalosis includes a systemic decrease in H+ concentration or increase in bicarbonate

ABG Reference values

• pH: 7.35-7.45
• pCO2: 35-45 mmHg
• PaO2: 75-100 mmHg
• HCO-3: 22-26 mEq/L
• SaO2: 94-100%

-Acidosis: Respiratory acidosis-elevation of pCO₂

• Respiratory alkalosis-depression of alveolar hyperventilation
• Metabolic acidosis—depression of HCO3- or an increase
• Metabolic alkalosis-elevation of HCO3- usually caused by acids

Acid-Base

• In respiratory acidosis, there is increased PCO2, increased carbonic acid, and increased bicarbonate
• In respiratory alkalosis, there is decreased PCO2, decreased carbonic acid, and decreased bicarbonate
• In metabolic acidosis, there are heavier breathings.
• Lighter breathing causes increased PCO2 in metabolic alkalosis

Acid disturbances

• Respiratory Acidosis includes hypoventilatory state and CNS depression issues.
• Respiratory alkalosis includes hyperventilation and anxiety
• Metabolic acidosis is diagnosed when a patient has DKA, Diarrhea and on Dialysis

Blood Pressure Regulation

• Blood pressure regulates to ensure adequate perfusion of body tissues and prevent damage to blood vessels
• Low pressures prevent sufficient flow for delivery of nutrients and removal of waste products
• High pressures damage delicate endothelial tissue, increase the likelihood of vascular disease and vascular rupture

Regulation Mechanism

• Maintaining the effective circulating volume and the vascular bed
• The kidneys and vascular system will activate to retain sodium
• kidney and vascular system - respond to pressure induced stretch of the vessel walls

RAAS (Renin-Angiotensin-Aldosterone System)

• Its RAAS Driven by hydrostatic pressure
• Renin initiates RAAS to replenish blood volume, sodium, and water, and raise blood pressure

This lesson discusses fluid, electrolyte, and acid-base balance: alterations, fluid exchange and capillary dynamics, acid-base imbalances (metabolic/respiratory acidosis/alkalosis), electrolyte imbalances, and blood pressure regulation with alterations in fluid balance. Body fluid compartments maintain electrochemical balance, where the number of negative charges equals positive charges.