Chapter 41: Fluid, Electrolyte, and Acid-Base Balance

Bonnie M. Wivell, MS, RN, CNS

Distribution of Body Fluids Intracellular = inside the cell; 42% of

body weight Extracellular = outside the cell, 17% of

body weight Interstitial = contains lymph; fluid between

cells and outside blood vessels Intravascular = blood plasma found inside

blood vessels Transcellular = fluid that is separated by

cellular barrier,

Body Fluid Compartments

Functions of Body Fluid Major component of blood plasma Solvent for nutrients and waste products Necessary for hydrolysis of nutrients Essential for metabolism Lubricant in joints and GI tract Cools the body through perspiration Provides some mineral elements

Composition of Body Fluids Body fluids contain Electrolytes

Anions – negative charge Cl, HCO3, SO4

Cations – positive charge Na, K, Ca

Electrolytes are measured in mEq Minerals are ingested as compounds and

are constituents of all body tissues and fluids

Minerals act as catalysts

Electrolytes in Body Fluids

Normal Values Sodium (Na+) 35 – 145 mEq/L Potassium (K+) 3.5 – 5.0 mEq/L Ionized Calcium (Ca++) 4.5 – 5.5 mg/dL Calcium (Ca++) 8.5 – 10.5 mg/dL Bicarbonate (HCO3) 24 – 30 mEq/L Chloride (Cl--) 95 – 105 mEq/L Magnesium (Mg++) 1.5 – 2.5 mEq/L Phosphate (PO4

---) 2.8 – 4.5 mg/dL

Movement of Body Fluids Osmosis = movement across a semi-

permeable membrane from area of lesser concentration to are of higher concentration; high solute concentration has a high osmotic pressure and draws water toward itself Osmotic pressure = drawing power of

water (Osmolality) Osmolarity = concentration of solution

Movement of Body Fluids

Colloid or Oncotic pressure = keeps fluid in the intravascular compartment by pulling water from the interstitial space back into the capillaries

Solutions Isotonic Solution

The same concentration as blood plasma; expand fluid volume without causing fluid shift

Hypotonic Solution Lower concentration than blood plasma; moves fluid

into the cells causing them to enlarge Hypertonic solution

Higher concentration than blood plasma; pulls fluid from cells causing them to shrink

Movement of Body Fluids Cont’d. Diffusion = Molecules move from higher

concentration to lower Concentration gradient

Filtration = water and diffusible substances move together across a membrane; moving from higher pressure to lower pressure

Edema results from accumulation of excess fluid in the interstitial space

Hydrostatic pressure causes the movement of fluids from an area of higher pressure to area of lower pressure

Active Transport Requires metabolic activity and uses

energy to move substances across cell membranes Enables larger substances to move into cells Molecules can also move to an area of

higher concentration (Uphill) Sodium-Potassium Pump

Potassium pumped in – higher concentration in ICF

Sodium pumped out – higher concentration in ECF

Regulation of Body Fluids

Homeostasis is maintained through Fluid intake Hormonal regulation Fluid output regulation

Fluid Intake Thirst control center located in the

hypothalamus Osmoreceptors monitor the serum osmotic

pressure When osmolarity increases (blood becomes

more concentrated), the hypothalamus is stimulated resulting in thirst sensation Salt increases serum osmolarity

Hypovolemia occurs when excess fluid is lost

Fluid Intake Average adult intake

2200 – 2700 mL per day Oral intake accounts for 1100 – 1400 mL

per day Solid foods about 800 – 1000 mL per day Oxidative metabolism – 300 mL per day

Those unable to respond to the thirst mechanism are at risk for dehydration Infants, patients with neuro or psych

problems, and older adults

Hormonal Regulation ADH (Antidiuretic hormone)

Stored in the posterior pituitary and released in response to serum osmolarity

Pain, stress, circulating blood volume effect the release of ADH Increase in ADH = Decrease in urine output =

Body saves water Makes renal tubules and ducts more

permeable to water

Hormonal Regulation Cont’d. Renin-angiotensin-aldosterone

mechanism Changes in renal perfusion initiates this

mechanism Renin responds to decrease in renal

perfusion secondary to decrease in extracellular volume

Renin acts to produce angiotensin I which converts to angiotensin II which causes vasoconstriction, increasing renal perfusion

Angiotensin II stimulates the release of aldosterone when sodium concentration is low

Hormonal Regulation Cont’d. Aldosterone

Released in response to increased plasma potassium levels or as part of the renin-angiotensin-aldosterone mechanism to counteract hypovolemia

Acts on the distal portion of the renal tubules to increase the reabsorption of sodium and the secretion and excretion of potassium and hydrogen

Water is retained because sodium is retained Volume regulator resulting in restoration of

blood volume

Hormonal Regulation Cont’d.

Atrial Natriuretic Peptide (ANP) ANP is a hormone secreted from atrial

cells of the heart in response to atrial stretching and an increase in circulating blood volume

ANP acts like a diuretic that causes sodium loss and inhibits the thirst mechanism

Monitored in CHF

Fluid Output Regulation

Organs of water loss Kidneys Lungs Skin GI tract

Fluid Output Regulation Cont’d. Kidneys are major regulatory organ of fluid

balance Receive about 180 liters of plasma to filter daily 1200 – 1500 mL of urine produced daily Urine volume changes related to variation in the

amount and type of fluid ingested Skin

Insensible Water Loss Continuous and occurs through the skin and lungs Can significantly increase with fever or burns

Sensible Water Loss occurs through excess perspiration Can be sensible or insensible via diffusion or perspiration

500 – 600 mL of insensible and sensible fluid lost through skin each day

Fluid Output Regulation Cont’d. Lungs

Expire approx 500 mL of water daily Insensible water loss increases in response

to changes in resp rate and depth and oxygen administration

GI Tract 3 – 6 liters of isotonic fluid moves into the GI

tract and then returns to the ECF 200 mL of fluid is lost in the feces each day

Diarrhea can increase this loss significantly

Regulation of Electrolytes

Major Cations in body fluids Sodium (Na+) Potassium (K+) Calcium (Ca++) Magnesium (Mg++)

Sodium Regulation

Most abundant cation in the extracellular fluid Major contributor to maintaining water

balance Nerve transmission Regulation of acid-base balance Contributes to cellular chemical reactions

Sodium is taken in via food and balance is maintained through aldosterone

Potassium Regulation Major electrolyte and principle cation in

the extracellular fluid Regulates metabolic activities Required for glycogen deposits in the liver

and skeletal muscle Required for transmission of nerve impulses,

normal cardiac conduction and normal smooth and skeletal muscle contraction

Regulated by dietary intake and renal excretion

Calcium Regulation Stored in the bone, plasma and body cells

99% of calcium is in the bones and teeth 1% is in ECF 50% of calcium in the ECF is bound to protein

(albumin) 40% is free ionized calcium Is necessary for

Bone and teeth formation Blood clotting Hormone secretion Cell membrane integrity Cardiac conduction Transmission of nerve impulses Muscle contraction

Magnesium Regulation Essential for enzyme activities Neurochemical activities Cardiac and skeletal muscle excitability Regulation

Dietary Renal mechanisms Parathyroid hormone action

50 – 60% of magnesium contained in bones 1% in ECF Minimal amount in cell

Anions Chloride (Cl-)

Major anion in ECF Follows sodium

Bicarbonate (HCO3-)

Is the major chemical base buffer Is found in ECF and ICF Regulated by kidneys

Anions Cont’d.

Phosphate (PO4---)

Buffer ion found in ICF Assists in acid-base regulation Helps to develop and maintain bones and teeth Calcium and phosphate are inversely

proportional Promotes normal neuromuscular action and

participates in carbohydrate metabolism Absorbed through GI tract Regulated by diet, renal excretion, intestinal

absorption and PTH

Regulation of Acid-Base Balance

Lungs and kidneys are our buffering systems

A buffer is a substance that can absorb or release H+ to correct an acid-base imbalance

Arterial pH is an indirect measure of hydrogen ion concentration

Greater concentration of H+, more acidic, lower pH

Regulation of Acid-Base Balance

Lower concentration of H+, more alkaline, higher pH

The pH is also a reflection of the balance between CO2 (regulated by lungs) and bicarb (regulated by kidneys)

Normal H+ level is necessary to Maintain cell membrane integrity Maintain speed of cellular enzymatic actions

Chemical Regulation Carbonic acid-bicarbonate buffer system is the

first to react to change in the pH of ECF H+ and CO2 concentrations are directly related ECF becomes more acidic, the pH decreases,

producing acidosis ECF receives more base substances, the pH

rises, producing alkalosis Lungs primarily control excretion of CO2

resulting from metabolism Kidneys control excretion of hydrogen and

bicarb

Biological Regulation

1. Buffer actions that occur

1. Exchange of K+ and H+2. Carbon dioxide goes

into RBCcarbonic acid (HCO3-)1. HCO3 ready to

exchange with Cl-3. Chloride shift within RBC

K+K+

K+

H+

H+

H+

H+ H+

Acidosis vs Alkalosis

Acidosis Acids have high H+ ions in solution

Alkalosis Bases have low H+ ion concentration

Acidity or Alkalinity of a solution measured by pH

Physiological Regulators Lungs

Regulate by altering H+ ions

Metabolic acidosis Metabolic alkalosis

Kidneys Regulate by altering

HCO3 and H+ ions

H+H+

H+H+

HCO3HCO3

HCO3HCO3

Causes of Electrolyte Imbalances Excessive sweating Fluid loss leading to

dehydration Excessive vomiting Diuretics like Lasix (K+

depletion) Massive blood loss Dehydration may go

unnoticed in hot, dry climates Renal failure

Sodium

Most abundant in extracellular space

Moves among three fluid compartments

Found in most body secretions

Na

NaNa

NaNa

Hyponatremia – Low Sodium

Seizures Personality changes Nausea/vomiting Tachycardia Convulsion Normal Na (135-

145)

Hypernatremia

Excessive Na in ECF Loss of water

Diarrhea Insensible water loss Water deprivation

Gain of Sodium Diabetes insipidus Heat stroke

Hypokalemia – Low Potassium

Severe leg cramps Flaccid muscles Fatigue Irregular pulse Chest discomfort EKG changes

T wave flattens Normal Potassium-

3.5-5

Hyperkalemia

CNS Nausea and

vomiting Peripheral Nervous

System Tremors, twitching

Heart Bradycardia,

peaked T wave

Hypocalcemia – Low Calcium

Tingling of fingers Tetany Muscle cramps Positive Trousseau’s

Carpal spasm Positive Chvostek’s

Contraction of facial muscle when facial nerve tapped

Hypercalcemia

Causes Prolonged immobility Osteoporosis Thiazide diuretics Acidosis

Signs/symptoms N/V, weakness Hypoactive reflexes Cardiac arrest

Hypomagnesemia Causes

Malnutrition Alcoholism Polyuria Pre-ecclampsia

Signs/symptoms Muscle tremor Hyperactive deep

reflexes Chvostek’s/Trousseau’s Difficulty breathing

Hypermagnesemia

Causes Renal failure Excessive intake

Signs/symptoms Low BP Muscle weakness Absent reflexes Bradycardia

Respiratory acidosis

pH ↓

PaCO2 ↑

HCO3 ↓

Respiratory alkalosis

pH ↑

PaCO2 ↓

HCO3 ↑

Metabolic acidosis pH ↓

PaCO2

HCO3 ↓

Metabolic alkalosis pH ↑

PaCO2

HCO3 ↑

Cheat Sheet Increase pH – alkalosis Decrease pH – acidosis Respiratory – CO2 Metabolic (kidneys)– HCO3 CO2 has an inverse relationship with pH When pH goes down, CO2 goes up HCO3 follows pH. If pH goes up so does HCO3 CO2 increases, pH decreases – resp. acidosis CO2 decreases, pH increases – resp. alkalosis HCO3 increases, pH increases – metabolic

alkalosis HCO3 decreases, pH decreases – metabolic

acidosis

Question An older client comes to the emergency

department experiencing chest pain and shortness of breath. An arterial blood gas is ordered. Which of the following ABG results indicates respiratory acidosis?1. pH - 7.54, PaCO2 – 28, HCO3 – 222. pH – 7.32, PaCO2 – 46, HCO3 – 243. pH – 7.31, PaCO2 – 35, HCO3 – 204. pH – 7.5, PaCO2 – 37, HCO3 - 28

Review

Acid/Base Imbalance Tutorial How do we assess for acid-base balance?

Assessment Nursing history

Age Prior Medical History

Acute illness Surgery Burns increase fluid loss Resp. disorder predisposes to resp. acidosis Head Injury can alter ADH secretion Chronic illness

Cancer CVD Renal disorders GI disturbances

Assessment Cont’d. Environmental factors affecting

fluid/electrolyte alterations Diet Lifestyle – smoking, ETOH Medications Physical Assessment

Daily weights I&O Vital signs

Laboratory Studies

Nursing Diagnosis Decreased cardiac output Acute confusion Deficient fluid volume Excess fluid volume Impaired gas exchange Risk for injury Deficient knowledge regarding disease

management Impaired oral mucous membrane Impaired skin integrity Ineffective tissue perfusion

Planning

Determine goals and outcomes Set priorities Collaborative care

MD Dietician Pharmacy

Implementation Health promotion

Education Acute care

Enteral replacement of fluids Restriction of fluids Parenteral replacement of fluids and electrolytes

TPN IV fluids and electrolyte therapy (crystalloids) Blood and blood components (colloids)

Blood groups and types Autologous transfusion Transfusion reactions

ABGs

Restorative Care

Home IV therapy Nutritional support Medication safety

Pt. education

Evaluation

Have goals been met? Have changes in assessment

occurred? Progress determines need to continue

or revise plan of care