Fluids, Electrolytes, and Diuretics - PathoPharm Exam 4

Fluid balance

• Definition: Equilibrium between fluid intake and

output to maintain hydration and proper fluid

distribution.

• Regulates:

• Blood pressure

• Nutrient transport

• Waste elimination

• Temperature control

• Disruptions: Can lead to heart failure, kidney

disease, and hypertension.

• Fluid Management: Critical for treatment and

maintaining balance.

Fluid compartments

The body has 2 main fluid compartments:

1. Intracellular Fluid (ICF) → fluid inside cells

• ~60% of total body water (TBW)

• Major electrolytes: K⁺, PO₄³⁻, Mg²⁺

2. Extracellular Fluid (ECF) → fluid outside cells

• ~40% of total body water

• Major electrolytes: Na⁺, Cl⁻, HCO₃⁻

• ECF is further divided into:

a. Intravascular (plasma) → fluid in blood

vessels (~20% of ECF)

b. Interstitial → fluid between cells (~75% of

ECF)

c. Transcellular → specialized fluids (CSF,

synovial, peritoneal) (~5% of ECF)

Fluid shifts and mechanisms

Definition: Movement of water between

compartments due to pressure or solute changes.

• Purpose: Maintains balance, adjusts hydration, and

supports nutrient/waste exchange.

• Key mechanisms:

• Hydrostatic Pressure, Oncotic Pressure,

Osmosis

• These mechanisms work together to regulate fluid

distribution between the ICF and ECF.

Hydroststaic pressure

Definition

• Force of fluid (blood) → pushing against vessel walls

• Function

• “Push force” → driven by blood volume + flow

• Along Capillaries

• Highest → arterial end (blood entering)

• Lowest → venous end (blood leaving)

• Direction of Movement

• Fluid moves → out of vessels → into tissues

• Intravascular → interstitial

• Supports → nutrient delivery

Oncotic pressure

Definition

• Force from plasma proteins (albumin) → pulling water into bloodstream

• Function

• Pull force” → maintains fluid in vessels

• If Albumin is Low

• ↓ oncotic pressure → weaker pull

• Fluid shifts → out of vessels → into tissues

• Leads to → edema

• Direction of Movement

• Fluid moves → from tissues → into vessels

• interstitial → intravascular

• Supports → fluid balance

Normal fluid balance

Hydrostatic + Oncotic = push–pull system → regulates fluid balance, prevents edema

• Hydrostatic (blood volume/flow)- pushes fluid out (intravascular → interstitial) → filtration

(nutrient delivery)

• Oncotic (albumin/proteins)- pulls fluid in (interstitial → intravascular) → reabsorption

(maintains volume, removes waste)

• Arterial end (high hydrostatic)

• hydrostatic > oncotic → net filtration to tissues

• Venous end (↓ hydrostatic)

• oncotic dominates → net reabsorption to vessels

• Lymphatics

• return excess interstitial fluid → venous circulation (subclavian veins)

• what doesn’t get reabsorbed goes to lymph → back to the veins

Fluid excess (edema)

↑ Hydrostatic → ↑ push out → fluid → tissues

• ↓ Oncotic (↓ albumin) → ↓ pull in → fluid stays in tissues

• Examples

• Heart failure → ↑ hydrostatic

• Liver/renal disease, burns → ↓ albumin

Too much out or not enough in

Fluid deficit (dehydration/volume loss)

• ↓ circulating volume → ↓ hydrostatic → ↓ perfusion

• Fluid shifts → from tissues → into vessels (compensatory)

• Examples

• Dehydration, hemorrhage, diuretics

Not enough volume in system

Indicators of fluid overload

Weight gain (rapid, especially in a

short period).

• Edema (swelling of feet, ankles, or

lungs).

• Shortness of breath (dyspnea, fluid

accumulation in lungs).

• Increased blood pressure (due to

excessive fluid in vascular system)

Indicators of fluid deficit

• Thirst (early sign).

• Dry skin and mucous

membranes (e.g., in the mouth, eyes).

• Low blood pressure (due to low

volume).

• Tachycardia (compensatory response).

• Decreased urine output (dark-

colored urine).

Third spacing

→ Fluid moves into spaces where it

cannot be used by the body

• Causes:

• Inflammation, burns, injury

• What Happens:

• Fluid leaves the vascular + interstitial

spaces → shifts into non-functional

areas

• Examples:

• Ascites (abdomen)

• Pleural effusion (pleural space)

• Pericardial effusion (pericardial sac)

• Key Effect:

• Fluid becomes “trapped” → not

available for circulation or exchange

→ ↑ risk of hypovolemia

ADH

• Function: Increases water retention by kidneys,

conserving fluid.

• Release: Triggered by high blood osmolarity

(e.g., dehydration).

Effect on Fluid Imbalances:

• Fluid Deficit: ADH ↑ to retain water.

• Fluid Overload: ADH ↓ to excrete excess water.

Purpose of IV fluids

• Restore fluid balance, treat dehydration and shock

• Correct electrolyte imbalances & support blood

volume

• Start with crystalloids then use colloids selectively if

response is inadequate

IV crystalloids

• Small molecules that move between compartments

• Provide short-term intravascular volume expansion

• First-line therapy in most cases

-Isotonic, hypotonic, hypertonic

IV Colloids

• Large molecules that remain in the vascular space

• Pull fluid into vessels by increasing oncotic pressure

• Provide longer-lasting volume expansion

• Colloids exert oncotic pull → more sustained volume expansion

than crystalloids

• Used selectively → cost, risk (e.g., fluid overload, transfusion

reactions)

Isotonic IV crystalloids

0.9% NS, LR, Ringer’s, D5W)*

• Stays in vascular space → no fluid shift

• Expands intravascular volume → ↑ perfusion

*D5W: isotonic in bag → acts hypotonic in body

• Use: hypovolemia, shock

Hypotonic IV crystalloids

(0.45% NS, 0.33% NS, 0.225% NS, D5W)*

• Water moves into cells → cells swell

• Vascular volume ↓ → risk hypotension

• Use: intracellular dehydration

Hypertonic IV crystalloids

(3% NS, 5% NS, D5NS, D5LR, D5 ½ NS,

D10W)

• Pulls water out of cells → cells shrink

• Intravascular volume ↑ → ↑ perfusion

• Use: severe hyponatremia, cerebral edema

Albumin IV colloid

(5%, 25%)

• Stays in vascular space → ↑ oncotic pressure

• Pulls fluid from interstitial → intravascular volume ↑

• Use: hypovolemia (after crystalloids), cirrhosis, large-

volume paracentesis

Blood products IV colloids

(PRBCs, Plasma, Platelets)

• Remain intravascular → restore volume + components

• PRBCs → ↑ oxygen-carrying capacity

• Plasma → replaces clotting factors → improves coagulation

• Platelets → ↑ platelet count → improves hemostasis

• Use: hemorrhage, anemia, coagulopathy

Electrolytes

Electrolytes are electrically charged minerals found in body

fluids.

• Why Do We Need Electrolytes?.

• Nerve Function: Enable electrical impulses for nerve

signaling, including cardiac conduction to regulate heart

rhythm.

• Muscle Contraction: Crucial for proper muscle function,

including the heart.

• Acid-Base Balance: Help maintain pH balance in body

fluids.

• Fluid Balance: Regulate water movement in cells, tissues,

and blood vessels

• Which Electrolytes Do We Have?

• The main electrolytes in the body include:

• Sodium (Na⁺), Potassium (K⁺), Chloride (Cl⁻),

Bicarbonate (HCO₃⁻)

• Calcium (Ca²⁺), Magnesium (Mg²⁺), Phosphate (PO₄³⁻)

Electrolytes and fluid shifts

How Electrolytes Affect Fluid Balance

• Na⁺ controls fluid outside cells (blood + tissues)

• Water follows sodium → moves toward higher Na⁺

• High Na⁺ (Hypernatremia)

• Water moves out of cells → into bloodstream

• Cells shrink → cellular dehydration

• Low Na⁺ (Hyponatremia)

• Water moves into cells

• Cells swell → edema

How Fluid Balance Affects Electrolytes

• Changes in fluid volume change electrolyte

concentration

Fluid overload

• Too much water → dilutes Na⁺ and K⁺

• Leads to hyponatremia or hypokalemia

• Dehydration

• Too little water → concentrates Na⁺

• Leads to hypernatremia

Hyponatremia

(Na⁺ < 135 mEq/L)

• Causes: SIADH, diuretics, HF/liver failure, ↑

intake

• S/S: headache, confusion, nausea → cramps

→ seizures

• Treatment

• Correct slowly → prevents demyelination

• Fluid restriction → SIADH

• 3% NaCl → severe

• Diuretics → fluid overload

• Treat cause

Hypernatremia

(Na⁺ > 145 mEq/L)

• Causes: dehydration, hyperaldosteronism,

Cushing’s, DI

• S/S: thirst, dry mouth → irritability → twitching

• Treatment

• Hypotonic fluids (0.45% NaCl)

• Oral fluids → if able

• Treat cause → monitor frequently

Hypokalemia

(K⁺ < 3.5 mEq/L)

• Causes: diuretics, vomiting,

diarrhea

• S/S

• Fatigue → muscle weakness

• Cramps → constipation

• Arrhythmias → U waves,

PVCs, torsades

• Treatment

• Oral/IV K⁺ → NEVER IV bolus

Hyperkalemia

(K⁺ > 5.0 mEq/L)

• Causes: renal failure, K⁺-sparing diuretics, acidosis

• S/S

• Weakness → fatigue

• Palpitations → arrhythmias (peaked T, wide QRS)

• Nausea → vomiting

• Treatment

• Calcium gluconate → stabilizes heart

• Insulin + dextrose → shifts K⁺ into cells

• Sodium bicarbonate → shifts K⁺ (acidosis)

• Diuretics or dialysis → remove K⁺

Hypochloremia

(Cl- < 98 mEq/L):

• Causes: Vomiting, metabolic alkalosis, diuretics

• S/S: Muscle twitching, weakness, Slow, shallow

breathing, Respiratory distress, confusion

• Treatment: Chloride-rich fluids, 0.9%

NaCl or LR.

Hyperchloremia

(Cl- > 108 mEq/L):

• Causes: Dehydration, renal failure, respiratory

acidosis

• S/S: Tachypnea, hypertension, Lethargy, deep and

rapid breathing (Kussmaul respirations)

• Treatment: Hypotonic fluids, sodium bicarbonate

to correct acidosis.

Metabolic Acidosis

)Low HCO3- < 22 mEq/L):

• Causes: Diarrhea, renal failure, metabolic acidosis

• S/S: Rapid breathing (Kussmaul respirations), Fatigue,

confusion, Nausea, vomiting

Metabolic Alkalosis

(High HCO3- > 28 mEq/L):

• Causes: Vomiting, metabolic alkalosis, comp. resp acidosis

• S/S: Slow, shallow breathing, Confusion, dizziness, Muscle

twitching, tetany

• Treatment: Correction of underlying cause, potassium

chloride, and fluids to correct electrolyte imbalances.

Hypocalcemia

Ca++ < 8.5 mg/dL):

• Causes: Hypoparathyroidism, vit D deficiency, CKD

• S/S: Muscle cramps, twitching, tetany

• Numbness/tingling around the mouth and in extremities

• Positive Chvostek's and Trousseau's signs

• Treatment: Calcium gluconate or calcium chloride IV.

Hypercalcemia

(Ca++ > 10.5 mg/dL):

• Causes: Hyperparathyroidism, cancer, excessive vit D

intake

• S/S: Lethargy, weakness, confusion

• Nausea, vomiting, constipation

• Kidney stones, bone pain

• Treatment: Hydration with IV

fluids, bisphosphonates, calcitonin.

Hypomagnesemia

(Mg++ < 1.5 mg/dL):

• Causes: Alcohol Use Disorder, malnutrition, diuretics

• S/S: Muscle cramps, weakness, tremors, seizures, confusion,

cardiac arrhythmias (e.g., Torsades de Pointes)

• Treatment: Magnesium sulfate IV or oral magnesium.

Hypermagnesemia

(Mg++ > 2.5 mg/dL):

• Causes: Renal failure, excessive Mg supplementation,

antacids/laxatives containing magnesium

• S/S: Hypotension, bradycardia, respiratory

depression, muscle weakness, drowsiness

• Treatment: Stop magnesium-containing medications,

administer calcium gluconate, possibly dialysis.

Hypophosphatemia

(PO4- < 2.5 mg/dL):

• Causes: Malnutrition, hyperparathyroidism, Alcohol Use

Disorder

• S/S: Muscle weakness, fatigue, Irritability, confusion, bone pain

or weakness

• Treatment: Oral or IV phosphate supplementation.

Hyperphosphatemia

(PO4- > 4.5 mg/dL):

• Causes: Renal failure, hypoparathyroidism, excessive

phosphate intake

• S/S :Itchy skin, muscle cramps, calcium phosphate deposits

in soft tissues (e.g., skin, eyes), Symptoms of hypocalcemia

• Treatment: Treat underlying cause, phosphate binders,

dietary restrictions.

Treatment of F&E imbalances

Treatment Goals to Restore Balance

1. Correcting electrolyte imbalances

2. Rehydrating the patient

3. Managing intravascular volume

Treatment Strategies

1. Fluid replacement (oral or IV) for

dehydration and third spacing

2. Diuretics for fluid overload and edema

-Diuretics – ↑ urine output

-Monitor electrolytes, especially K+

Furosemide

Pharmacological Class: Loop Diuretic

• MOA: Inhibits sodium and chloride reabsorption in the

loop of Henle & distal tubule, enhancing water

excretion.

• Uses: Edema (heart failure, liver cirrhosis, renal disease),

pulmonary edema, hypertension.

• ADR: Hypokalemia, hyponatremia, dehydration,

hypotension, ototoxicity, dizziness.

• Nursing Considerations:

• Administer slowly (IV) to prevent ototoxicity; do

not exceed 4 mg/min.

• Monitor electrolytes (especially K), renal function, and

blood pressure.

• Educate patient to increase dietary K intake to prevent

hypokalemia.

• Administer in the morning to avoid nocturia.

Hydrochlorothiazide (HCTZ)

Pharmacological Class: Thiazide Diuretic

• MOA: Inhibits sodium and chloride reabsorption in

the distal renal tubule, leading to increased

excretion of Na, Cl, and water.

• Uses: Hypertension, mild edema, kidney stones

prevention.

• ADR: Hypokalemia, hyponatremia,

hyperglycemia, hyperuricemia, photosensitivity,

dizziness.

• Nursing Considerations:

• Monitor blood pressure, electrolytes and blood

glucose.

• Educate on sun protection due to

photosensitivity.

• Administer in the morning to prevent nocturia and

enhance efficacy.

Spironolactone

Pharmacological Class: Mineralocorticoid

Receptor Antagonist Diuretic

• MOA: Antagonizes aldosterone in the distal renal

tubules, promoting sodium and water excretion while

conserving potassium.

• Uses: Heart failure, hypertension, edema, primary

hyperaldosteronism, acne, hirsutism.

• ADR: Hyperkalemia, gynecomastia and

menstrual irregularities, dizziness, rash.

• Nursing Considerations:

• Monitor potassium levels carefully due to risk of

hyperkalemia.

• Avoid potassium supplements and salt substitutes

high in potassium.

• Take with food to reduce gastrointestinal irritation

and improve absorption.

Acetazolamide

• Pharmacological Class: Carbonic Anhydrase Inhibitor

• MOA: Inhibits carbonic anhydrase, reducing sodium

bicarbonate reabsorption in the proximal tubule, leading

to diuresis

• Uses: Glaucoma, altitude sickness, metabolic alkalosis, epilepsy.

• ADR: Hypokalemia, hyponatremia, metabolic acidosis, kidney

stones, drowsiness, tingling sensation.

• Nursing Considerations:

• Monitor electrolytes, renal function, and for signs of

metabolic acidosis.

• Encourage adequate hydration to reduce risk of kidney

stones.

• Monitor for neurological effects (tingling or dizziness) as

common side effects.

Mannitol

• Pharmacological Class: Osmotic Diuretic

• MOA: Increases osmotic pressure in the renal

tubules, drawing water into the tubules and promoting

diuresis.

• Uses: Cerebral edema, increased intraocular

pressure (glaucoma).

• ADR: Hyponatremia, hypokalemia, dehydration,

pulmonary edema, headache.

• Nursing Considerations:

• Administer through a filter to prevent

crystallization, especially in cold conditions.

• Monitor vital signs, fluid balance, electrolytes, and

renal function closely.

• Assess for pulmonary edema (shortness of breath,

crackles), especially in high-risk patients (e.g., heart

failure).

Sodium

• Major extracellular cation

• Fluid balance → nerve transmission → BP regulation

Potassium

• Major intracellular cation

• Nerve transmission → muscle contraction → cardiac rhythm → fluid & acid-base balance

Chloride

Function: Major extracellular anion. Works

with sodium to help maintain osmotic

pressure and fluid balance.

Carbonate

Function: Key role in acid-base balance as a buffer to

maintain pH in the body. Works with carbonic acid to

maintain homeostasis

Calcium

Function: Essential for bone/tooth

formation, neuromuscular function, blood clotting.

Helps maintain cellular function and cardiac rhythm.

Magnesium

Function: Important for neuromuscular

transmission, enzyme function, and ATP production.

Helps regulate cardiac rhythm and muscle function.

Phosphate

Function: Key component of ATP, DNA, and RNA. Plays a

role in bone health, acid-base balance, and energy

metabolism.