Fluid, Electrolyte, and Acid-Base Balance Notes

ABG's

ICF

Fluid within cells; most of the body's fluids.

ECF

Fluid outside cells; intravascular (plasma) and interstitial (lymph).

Membrane Function

Selectively permeable, controls solute movement, maintains composition.

Diffusion

Movement from high to low concentration; necessary for transport.

Facilitated Diffusion

Carrier protein transports molecules to lower concentration.

Active Transport

Carrier proteins transport substances from low to high concentration with energy.

Filtration

Water and solutes move from high to low pressure.

Osmosis

Water moves from less to more concentrated solution to balance.

Osmolarity

Concentration by particles per kg of water; controls water movement.

Aging Kidney

Adjusts slower to acid-base, fluid, and electrolyte changes.

Older Adults & Thirst

Reduced thirst; may lead to chronic dehydration.

Body Water with Age

Total body water declines; greatest loss from ICF.

Age & Fluid Balance

Limited reserves to maintain fluid balance during losses.

Later Life Fluid Needs

30 mL/kg (55-65 yrs), 25 mL/kg (65+ yrs).

Water Content

Largest body component; varies by age, sex, fat.

Electrolyte

Develops electrical charge in water (Na, K, Cl, Ca, Mg).

Sodium (Na+)

136-145 mEq/L; regulates fluids, muscle, nerve, acid-base.

Hyponatremia

Low serum Na; headache, weakness, cramps, hypotension.

Hypernatremia

High serum Na; thirst, flushed, dry, low output, restlessness.

Potassium (K+)

3.5-5.0 mEq/L; for osmolarity, nerve, protein synthesis.

Hypokalemia

Low K; GI, renal, cardio, neuro disturbances, dysrhythmias.

Hyperkalemia

High K; dysrhythmias, diarrhea, cramps, low urine output.

Calcium (Ca2+)

9.0-10.5 mg/dL; nerve, muscle, bones, teeth.

Hypocalcemia

Low Ca; neuromuscular irritability, cramps, +Trousseau, +Chvostek.

Hypercalcemia

High Ca; anorexia, nausea, thirst, fatigue, confusion.

Trousseau's Sign

Carpal spasm with inflated BP cuff; indicates hypocalcemia.

Chvostek's Sign

Facial spasm when tapping nerve; indicates hypocalcemia.

Magnesium (Mg2+)

1.3-2.1 mEq/L; metabolism, energy, neural transmission.

Hypomagnesemia

Low Mg; Decreased GI absorption, excessive GI/urinary loss.

Hypermagnesemia

High Mg; excessive intake, renal failure, preeclampsia.

Nonelectrolytes

No charge; urea, protein, glucose, creatinine, bilirubin.

Daily Fluid Balance

Intake equals output in healthy adults.

Urine Volume

1-2 L/day or 1 mL/kg/hr.

Lung Water Loss

300-400 mL/day via evaporation.

GI Tract Fluid Loss

100-200 mL/day.

Kidney Urine Output

About 1500 ml/day.

Urine Studies

pH, specific gravity, osmolality, creatinine clearance, Na, K.

Blood Studies

Hct, creatinine, BUN, albumin, electrolytes, blood gas.

Hemoconcentration

Dehydration.

Hemodilution

Fluid overload.

Compensation

Body corrects pH imbalances; full: pH 7.35-7.45.

Chemical Buffers

Bicarbonate and intracellular fluid.

Protein Buffers

Albumin and globulins.

Respiratory Buffers

Hyperventilation/hypoventilation.

Respiratory Acidosis

Hypoventilation; opioid, brain tumor, obstruction.

Resp. Acidosis S/S

Tachycardia/hypertension progressing to bradycardia/hypotension.

Respiratory Alkalosis

Hyperventilation; fear, anxiety, trauma, hypoxia.

Resp. Alkalosis S/S

Tachypnea, numbness, tinnitus, tachycardia.

Metabolic Acidosis

Too many H+ or loss of HCO3-; starvation, diarrhea, renal failure.

Met. Acidosis S/S

Altered LOC, headache, vomiting, cardiac dysrhythmias.

Metabolic Alkalosis

Increased HCO3- or loss of H+; suctioning, vomiting, diuretics.

Met. Alkalosis S/S

Headache, irritability, lethargy, slow respirations.

Acid-Base Imbalance Care

Treat the underlying cause.

ABG - ROME

Respiratory Opposite Metabolic Equal.

Kidney Function

Filtration, reabsorption, secretion, renin/aldosterone.

Aldosterone Function

Retain sodium and water.

ADH Function

Reabsorb water; concentrate urine.

ANF Function

Excrete sodium and water; vasodilation.

Thirst Trigger

Increased osmolality stimulates hypothalamus to trigger thirst.

Fluid Balance & Pulse

Pulse rate changes indicate fluid/electrolyte imbalance.

Tachypnea Indicates…

Fluid volume excess (pulmonary edema).

Fever Indicates…

Metabolic rate and fluid loss.

Orthostatic Hypotension

20 mm Hg drop; indicates fluid volume deficit.

Skin Turgor Assessment

Pinch skin; slow flattening indicates dehydration.

Tongue Turgor

Longitudinal furrows indicate fluid volume deficit.

Hypovolemia Risk Factors

Vomiting, diarrhea, diuretics, burns, hemorrhage.

Dehydration Causes

Hyperventilation, fever, insufficient intake.

Hypovolemia Findings

Tachycardia, hypotension, dizziness, thirst, oliguria.

Hypovolemia Lab Results

Increased Hct, BUN, urine specific gravity, blood sodium.

Hypovolemia Management

Oral or IV rehydration, monitor I&O and vital signs.

Hypovolemic Shock

Significant fluid loss; decreased MAP.

Overhydration

Excess fluid intake or ineffective removal.

Overhydration Risks

HF, kidney disease, SIADH.

Overhydration Findings

Tachycardia, hypertension, edema, altered LOC.

Overhydration Lab Results

Decreased Hct, Hgb, blood osmolarity, urine sodium.

Overhydration Management

Monitor I&O, daily weight, restrict sodium/fluids.

Pulmonary Edema

Severe fluid overload; anxiety, dyspnea, crackles.

Aging & Fluid Balance

Kidney slower, reduced thirst, decreased body water.