Human Physiology: Fluid and Electrolyte Balance

Fluid and Electrolyte Balance: Balance and Disturbance

• Fluid and electrolyte balance is crucial for life and homeostasis
• Disorders of fluid and electrolyte balance affect healthy people and those who are ill. Examples include strenuous exercise, increased fluid and sodium loss, and high environmental temperatures.
• Homeostasis is the maintenance of a constant internal equilibrium in a biological system involving positive and negative feedback mechanisms.
• Body fluid is distributed between Intracellular fluid (ICF), which is inside the cell (~67%) and Extracellular fluid (ECF), which is outside the cell (~33%). ECF further divides into interstitial fluid (~26%) and plasma (~7%).
• Total body water = 60% of body weight. Adult body contains ~28 liters of intracellular water, ~10 liters of interstitial fluid, and ~3.5 liters of plasma.

Objectives

• Identify the distribution of fluids and electrolytes throughout the body
• Describe the causes, manifestations, management, and interventions for fluid/electrolyte abnormalities
• Identify types and usage of I.V fluids
• Identify complications related to I.V therapy
• Identify nursing considerations for patients receiving I.V therapy

Outline

• Definition of fluid & electrolyte balance, homeostasis
• Distribution of body fluids
• Factors affecting fluid & electrolytes in the body
• Composition of body fluids
• Processes of fluid & electrolyte balance regulation
• Fluid imbalance - Fluid volume deficit(FVD) & dehydration, Fluid volume excess (FVE) & overhydration
• Edema
• Electrolyte imbalance
• Nursing process for fluid & electrolyte imbalance

Introduction

• Fluid and electrolyte balance depends on dynamic processes crucial for life and homeostasis.
• Potential and actual disorders of fluid and electrolyte balance occur in every setting, affecting healthy people with diverse conditions including increased fluid/sodium loss with exercise and temperature, or inadequate fluid/electrolyte intake in ill people.
• Homeostasis involves positive and negative feedback mechanisms.

Fluid distribution/Compartments

• Intracellular fluid (ICF)
• Extracellular fluid (ECF)
• Intracellular fluid (2/3 of body water)
• Extracellular fluid (1/3 of body water)
• Blood (intravascular, 1/12 of ECF)
• Interstitial (11/12 of ECF)

Systemic Routes of Gains and Losses

• Healthy individuals gain and lose fluids nearly equal amounts daily.
• Fluid intake orally, as water, in food, and from oxidation of food accounts for ~2500mL.
• Fluid output through urine, stool, lungs, and skin (~2500 mL).

Systemic Routes of Gains and Losses (Further detail)

• Kidneys - daily urine output ~1-2 liters
• Skin - insensible perspiration accounts for ~300 mL
• Lungs - insensible water loss from breathing is ~300 mL
• Gastrointestinal tract - ~100-200 mL

Laboratory Tests for Evaluating Fluid Status

• Osmolality: concentration of fluid affecting water movement between compartments (~275-290 mOsm/kg in healthy adults)
• Urine-specific gravity: measures kidney's ability to excrete/conserve water (~1.010 to 1.025).
• Blood Urea Nitrogen (BUN): end product of protein metabolism by liver (~10 to 20 mg/dL).
• Creatinine: end product of muscle metabolism (~0.7-1.4 mg/dL).
• Hematocrit % of red blood cells in whole blood (42% to 52% for men and 35% to 47% for women)

Homeostatic Mechanisms

• Kidney functions: normally filters 180 L of plasma and excretes 1-2 L of urine daily
• Heart and blood vessels: pumps blood through kidneys under enough pressure for urine formation
• Lung function: Removes ~300 mL water daily through exhalation
• Pituitary functions: ADH released from hypothalamus conserved water
• Adrenal: Increased aldosterone causes retention of sodium and water

Other Mechanisms

• Baroreceptors in atrium respond to changes in blood volume and regulate sympathetic and parasympathetic neural activity
• Renin-Angiotensin-Aldosterone System (RAAS)
• Antidiuretic Hormone (ADH) and Thirst
• Osmoreceptors in hypothalamus senses change in sodium concentration
• Natriuretic Peptides affect fluid volume and cardiovascular functions

Fluid Regulation Cycle

• Relationship between variables like blood volume, serum osmolality, and ADH production for regulating fluid
• Variables such as arterial blood pressure and renal perfusion.
• Relationship between variables and factors like ADH, aldosterone, renal blood flow, GFR, urinary excretion of water and sodium, and blood pressure.

Fluid Volume Deficit (FVD), Hypovolemia

• Loss of ECF volume exceeds fluid intake, ratio of electrolytes to water remains the same.
• Conditions caused by vomiting, diarrhea, GI suctioning, sweating, decreased intake, third-space fluid shifts, Burns, ascites with liver dysfunction, diabetes insipidus, adrenal insufficiency, osmotic diuresis etc.

Signs and Symptoms of FVD

• Weight loss
• Decreased skin turgor (skin pinching does not rebound quickly).
• Concentrated urine
• Prolonged capillary filling time
• Low central venous pressure (CVP)
• Flattened neck veins
• Tachycardia, Hypotension
• Dry skin and cracked lips
• Sunken eyes
• Muscle cramps
• Thirst
• Weakness
• Dizziness
• Changes in mental status

Medical Management of FVD

• Oral fluids for mild cases
• I.V Fluids for acute cases (isotonic such as lactated ringers or 0.9% normal saline).
• Switch to hypotonic solution (0.45%NS) once patient is normotensive.

Nursing Care of FVD

• Monitor vital signs
• Weigh daily
• Monitor I&O
• Assess ability to ambulate
• Check skin/tongue turgor
• Increase oral fluid intake
• Offer oral rehydration solutions
• Provide frequent mouth care

Hypervolemia (Fluid Volume Excess (FVE))

• Abnormal retention of water and sodium in ECF, leads to an increase in total body sodium and water
• Causes include excessive fluid intake, impaired kidney function, heart failure, cirrhosis of the liver etc.

Signs and Symptoms of FVE

• Weight gain
• Peripheral edema
• Crackles (fluid in lungs)
• Elevated CVP or distended neck veins
• Shortness of breath
• Hypertension
• Tachypnea
• Increased urine output

Medical Management of FVE

• Limiting sodium and fluid intake
• Administering diuretics (such as lasix)
• Dialysis for severe cases
• Treating underlying causes of fluid retention

Nursing Care for FVE

• Monitor vital signs, weight, and I&O closely
• Assess breath sounds
• Assess for edema
• Monitor serum electrolytes
• Provide regular rest periods
• Avoid medications containing sodium
• Elevate affected limbs

Edema

• Accumulation of fluid in interstitial space causing soft tissue swelling
• Generalized: throughout the body
• Localized: specific body part
• Grade 1: Immediate rebound with 2 mm pit
• Grade 2: Less than 15-second rebound with 3-4 mm pit
• Grade 3: Rebound greater than 15 seconds but less than 60 seconds with 5-6 mm pit
• Grade 4: Rebound between 2-3 minutes with 8 mm pit

Pathophysiology of Edema

• Increased capillary fluid pressure (due to venous obstruction, heart failure)
• Decreased capillary oncotic pressure (due to low albumin, liver disease, malnutrition)
• Increased interstitial oncotic pressure (due to inflammatory conditions, lymphatic obstruction)

Types of Edema

• Localized: restricted to a specific body part (e.g., ankle edema in rheumatoid arthritis)
• Generalized: affecting multiple body areas (e.g., cardiac failure, kidney injury)
• Anasarca: extreme form of generalized edema (e.g., severe heart failure, liver disease)

Ascites

• Accumulation of fluid in the peritoneal cavity
• Causes include cirrhosis, nephrotic syndrome, and certain malignancies
• Clinical manifestations: abdominal distension, shortness of breath, discomfort, and respiratory difficulties
• Management includes addressing underlying cause, sodium and fluid restriction, diuretic therapy, paracentesis, and nutritional support

Assessing and Monitoring Edema

• Visual inspection: Swelling in dependent areas (feet, ankles, sacral region)
• Pitting Test: Apply firm pressure for 5 seconds. Measures the depth of the pit and time of rebound.
• Circumference Measurement: Use a tape measure to track changes in limb circumference.
• Weight Monitoring: Daily weight measurements help track fluid retention.

Management Strategies for Edema in FVE

• Diuretic Therapy: Medications like furosemide increase urine output and reduce fluid volume.
• Sodium & Fluid Restriction: Limiting sodium and restricted fluid intake limits fluid retention.
• Limb Elevation and Compression: Elevating affected limbs helps venous return and fluid mobilization while using compression stockings.
• Advanced Interventions: Paracentesis for ascites and dialysis for severe cases

Nursing Care of Patients with Edema

• Salt restricted diet
• Using diuretics as ordered
• Monitor I&O
• Weigh daily
• Positioning changes
• Skin care
• Elevation of edematous limbs
• Avoiding prolonged sitting/standing

Parenteral Fluid Therapy

• Purpose: Administer fluids when other routes are unavailable, to provide fluids, electrolytes & nutrients to meet daily requirements, replace water/electrolytes and administer medications or blood products
• Types of Intravenous solutions
• Isotonic: similar osmolality to ECF (e.g., 0.9% normal saline, D5W)
• Hypotonic: lower osmolality than ECF (e.g., 0.45% normal saline)
• Hypertonic: higher osmolality than ECF (e.g., 3% saline, D10W)

Nursing Management of the Patient Receiving Intravenous Therapy

• Perform venipuncture to gain access to venous system, use appropriate cannula
• Initiate infusion with correct fluid type, amount and rate
• Closely monitor the patient's response to the fluids considering fluid volume, content and clinical status.

Complications of I.V. Therapy

• Infiltration: Fluid leakage into surrounding tissues from vein
• Infection: Signs of infection at the site (purulent drainage, erythema, warmth, hardness, fever)
• Phlebitis: Inflammation of the vein (redness, swelling, tenderness, sluggish flow)
• Air Embolism: Air entering vein (decreased blood pressure, increased pulse, respiratory distress, increased ICP, loss of consciousness)

Electrolytes Imbalances

• Electrolytes are active chemical constituents in bodily fluids carrying positive or negative charges. Examples include sodium, potassium, calcium, magnesium, chloride, bicarbonate, sulfate and proteins.
• Electrolyte concentration measured in milliequivalents(mEq or mmol per liter).

Roles of Major Electrolytes

• Fluid balance in bodily fluids
• Transmission of nerve impulses
• Muscular function
• Acid-base balance regulation
• Blood clotting

Electrolyte Concentrations (Table)

• Normal electrolyte concentrations for extracellular and intracellular fluids.

Sodium Imbalances

• Sodium is the most abundant electrolyte in extracellular fluid (ECF).
• Sodium deficit (hyponatremia):Serum sodium level less than 135 mEq/L. Causes include loss of GI fluids, excessive diuretic use, certain medications (anticonvulsants, such as carbamazepine), adrenal insufficiency, and excessive water supplements for patients receiving hypotonic tube feedings
• Sodium excess (hypernatremia): Serum sodium level greater than 145 mEq/L due to water deprivation in patients unable to drink, hypertonic tube feedings, diabetes insipidus, and excessive use of corticosteroids

Potassium Imbalances

• Potassium is an important electrolyte in intracellular fluid (ICF).
• Potassium deficit (hypokalemia) : Serum potassium level less than 3.5 mEq/L. Causes include potassium-losing diuretics (thiazides, loop diuretics), GI losses (vomiting, diarrhea), hyperaldosteronism, and inadequate dietary consumption
• Potassium excess (hyperkalemia):Serum potassium level greater than 5.0 mEq/L. Causes include renal failure, fluid volume deficit, iatrogenic administration of potassium, adrenal insufficiency, and use of potassium-sparing diuretics.

Calcium Imbalances

• Calcium is essential for nerve impulse transmission, muscle function, and blood clotting
• Calcium deficit (hypocalcemia):Serum calcium level less than 8.6 mg/dL. Causes include hypoparathyroidism, malabsorption, massive transfusion of citrated blood, pancreatitis, prolonged diarrhea, and diuretic phase of renal failure
• Calcium excess (hypercalcemia): Serum calcium level greater than 10.2 mg/dL. Causes include renal failure, hyperparathyroidism, vitamin D excess, prolonged immobilization, overuse of calcium supplements, and corticosteroid therapy.

Test your knowledge on human physiology with a focus on fluid and electrolyte balance. This quiz covers topics such as normal ranges for serum osmolality, urine-specific gravity, and the roles of hormones in water conservation. Perfect for students studying human biology or health sciences.