Module 2 Fluid and Sodium

Body Fluid Compartment Distribution

ICF: 70% (within cells); ECF: 30% (interstitial, intravascular, transcellular)

Isotonic IV Fluid Mechanism

Same solute concentration as cells; no net fluid movement; maintains cell volume

Isotonic IV Fluid Uses

↑ extracellular volume during blood loss, dehydration, fluid deficit

Isotonic IV Fluid Examples

0.9% Normal Saline (NS), D5W, Lactated Ringer's

Hypotonic IV Fluid Mechanism

Lower solute concentration than cells; fluid moves INTO cells causing swelling

Hypotonic IV Fluid Use

Treat cellular dehydration (hypernatremia); rehydrate intracellular space

Hypotonic IV Fluid Examples

0.45% NS (half normal), 0.225% NS (quarter normal)

Hypertonic IV Fluid Mechanism

Higher solute concentration than cells; pulls fluid OUT of cells into vascular space

Hypertonic IV Fluid Risks

High risk for pulmonary and cerebral edema; must infuse slowly

Hypertonic IV Fluid Use

Severe hyponatremia treatment

Hypertonic IV Fluid Examples

3% NS, D10W, D5NS, D5LR

Crystalloids vs Colloids Function

Crystalloids: move fluid between ICF/ECF; Colloids: pull fluid from interstitial to intravascular (plasma expanders)

Colloid Examples and Uses

Albumin, FFP, PRBCs; used in shock, severe hypovolemia when large crystalloid volumes not tolerated

Hydrostatic vs Oncotic Pressure

Hydrostatic: pushes fluid OUT of capillaries; Oncotic (albumin): pulls fluid INTO vessels

Second Spacing (Edema) Causes

↑ hydrostatic pressure (HTN, fluid overload); ↓ oncotic pressure (liver disease/low albumin)

Third Spacing Definition

Abnormal fluid accumulation in spaces normally without large fluid amounts (ascites, pleural effusion, pericardial effusion)

Third Spacing Causes

Inflammation, trauma, infection, heart failure, liver disease

Third Spacing Consequences

Swelling, impaired organ function, breathing difficulties, ↑ infection risk

Isotonic Dehydration Mechanism

Equal water and electrolyte loss; ↓ circulating blood volume; inadequate tissue perfusion

Hypertonic Dehydration Mechanism

More water loss than electrolytes; ↑ plasma electrolyte concentration; fluid shifts from ICF to plasma; cells shrink

Hypotonic Dehydration Mechanism

More electrolyte loss than water; fluid shifts from plasma into cells; cells swell

Isotonic Dehydration Causes

↓ intake of fluids/solutes, fluid shifts between compartments, excessive isotonic fluid loss

Hypertonic Dehydration Causes

↑ fluid loss from perspiration, hyperventilation, ketoacidosis, prolonged fever, diarrhea, ESRD, diabetes insipidus

Hypotonic Dehydration Causes

Chronic illness, excessive fluid replacement, renal disease, chronic malnutrition

Fluid Volume Deficit Lab Findings

↑ serum osmolality, ↑ hematocrit (concentration), ↑ BUN, ↑ serum sodium (concentration), ↑ urine specific gravity

Fluid Volume Deficit Assessment

Weak/thready pulse, ↓ BP, orthostatic hypotension, flat neck veins, ↓ RR, lethargy, muscle weakness, ↓ urine output, ↓ skin turgor, dry mouth, thirst

Fluid Volume Deficit Replacement Strategy

Replace with opposite fluid type: isotonic→isotonic; hypertonic→hypotonic; hypotonic→hypertonic

Isotonic Fluid Overload (Hypervolemia)

Excessive ECF causing circulatory overload and interstitial edema; common in cardiac problems

Hypertonic Fluid Overload

Fluid drawn from ICF; ICF contracts, ECF expands; rare; caused by excessive sodium intake

Hypotonic Fluid Overload (Water Intoxication)

Excessive fluid moves into ICF diluting electrolytes

Isotonic Overload Causes

Inadequately controlled IV fluids, kidney disease, long-term corticosteroid therapy

Hypertonic Overload Causes

Excessive sodium ingestion, rapid infusion of hypertonic saline, excessive sodium bicarb

Hypotonic Overload Causes

Early kidney disease, heart failure, SIADH, inadequately controlled IV fluids

Fluid Volume Overload Lab Findings

Decreased lab values (opposite of deficit; dilution effect)

Fluid Volume Overload Assessment

Bounding pulse, ↑ BP, distended neck veins/JVD, ↑ RR, headache, edema, possibly ↑ or ↓ urine output

Fluid Volume Overload Management

Restrict fluid/sodium intake, diuretics (thiazide for mild, loop/K-sparing for severe), monitor electrolytes, dialysis for severe/renal failure

Sodium and Water Relationship

Sodium and water always travel together; sodium regulates water distribution

Sodium Regulation Mechanisms

ADH, thirst, renin-angiotensin-aldosterone system (RAAS)

Euvolemic Hyponatremia

Kidneys retain water without sodium; ↑ ECF but no excess fluid retention (normal volume); caused by adrenal insufficiency

Hypovolemic Hyponatremia

↓ both water and sodium volume; caused by diuretics, GI losses (NG suction, vomiting, diarrhea), burns, excessive sweating

Hypervolemic Hyponatremia

↑ both sodium and water (water increases more); common in renal failure, liver failure, excessive sodium infusion

Hyponatremia Clinical Manifestations

CNS symptoms (seizures, stupor, lethargy, confusion), GI cramping, poor appetite, muscle spasms, ↓ urine output, orthostatic hypotension, shallow respirations

Hyponatremia Memory Cue

"Think sodium, think neuro" - neurologic manifestations prominent

Hypovolemic Hyponatremia Treatment

3% hypertonic saline (ICU/central line due to vein irritation and fluid overload risk)

Hypervolemic Hyponatremia Treatment

Fluid restriction, diuretics to excrete water (not sodium), dialysis if renal impairment

Euvolemic Hyponatremia Treatment

Fluid restriction, encourage sodium-rich foods

Hyponatremia Correction Caution

Monitor sodium level closely; too rapid increase causes harm

Cerebral Salt Wasting Syndrome

Significant head trauma causes excessive urinary sodium excretion leading to hyponatremia

Hypernatremia Causes

↑ sodium intake (tube feedings with inadequate water, over-infusion hypertonic fluids), difficulty excreting sodium, fluid loss, lack of fluid intake

Primary Hypernatremia Protection

Thirst mechanism; at-risk patients: confused, limited fluid access, unable to ask for fluids

Hypernatremia High-Risk Populations

Patients unable to access fluids independently (confused, immobile, communication impaired); nurse must offer fluids proactively

Hypernatremia Other Causes

Hyperventilation (respiratory alkalosis), hypercortisolism (sodium retention), ↑ aldosterone (regulates Na/K balance)

Hypernatremia Clinical Manifestations

Fatigue, restlessness, muscle twitching, seizure risk (high levels), fluid overload, ↓ urine output, extreme thirst, dry mucous membranes

Hypernatremia Management

↑ fluids slowly with isotonic/hypotonic solutions; cells dehydrated; rapid infusion risks cerebral edema

Hypernatremia Safety Considerations

Patient safety due to CNS changes (fall risk from confusion)