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, Transcellular fluids: CSF, pleural, GI, intraocular, peritoneal, and synovial Loss of transcellular fluid can produce fluid and electrolyte disturbances

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 Body fluids made up of electrolytes Electrolyte is an element Separates into ions – cations (positive, Na+, K+, Ca+) and anions (negative, Chloride, bicarbonate [HCO3} Minerals (Example: Iron and Zinc) Initiate nerve responses Initiate muscle contractions Metabolize nutrients in foods Regulate electrolyte balance Regulate hormone production Strengthen bones Too much or too little causes serious consequences

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 Hypotonic Solution Hypertonic 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 Concentration gradient = the difference between the two concentrations (i.e. movement of oxygen and CO2 between the alveoli and blood vessels in the lungs

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 Hypovolemia occurs when excess fluid is lost 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-) Bicarbonate (HCO3-) 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 Buffer actions that occur Exchange of K+ and H+ Carbon dioxide goes into RBCcarbonic acid (HCO3-) HCO3 ready to exchange with Cl- Chloride shift within RBC H+ H+ K+ K+ K+ Hydrogen ion has positive charge and must be exchanged by another positively charged ion – usually K+ Excessive acid – H+ enter cell and K+ leaves it’s house into extracellular fluid (ECF), resulting in elevated K+ Carbon dioxide shifts into RBC’s ---- produce carbonic acid ----disassociates into H+ and bicarbonate ions H+ attach to Hgb and bicarbonate (HCO3-) becomes ready to exchange for chloride (Cl-) Chloride shift within RBCs Normally Chloride travels from the Hgb to plasma during inspiration and plasma to Hgb on expiration Bicarb diffuses in and out of the cells H+ H+ H+

Acidosis vs Alkalosis Acidosis Alkalosis Acids have high H+ ions in solution Alkalosis Bases have low H+ ion concentration Acidity or Alkalinity of a solution measured by pH Higher H+ ions the more acidic and the lower the pH Water has a pH of 7 and is neutral Death at each end of spectrum Urine pH is 4.6-8 (check)

Physiological Regulators Lungs Regulate by altering H+ ions Metabolic acidosis Metabolic alkalosis Kidneys Regulate by altering HCO3 and H+ ions H+ H+ HCO3 HCO3 Lungs – Regulate H+ ions Alter rate, depth of respirations to correct Metabolic acidosis [high H+] Respirations increase to exhale more CO2 [which is a potential acid, carbonic acid – H2CO3]---carbonic acid level falls which results in homeostatis or becoming less acidic Happens quickly Metabolic alkalosis (bicarbonate levels are high) --respirations reduced, CO2 retained causing carbonic levels to raise Kidneys – take longer to regulate (few hours to days) Regulate bicarbonate production Acidosis – excessive H+, kidneys reabsorb HCO3 (bicarbonate) and excrete H+ ions Alkalosis – Low H+ ions – kidneys excrete HCO3 and retain H+ ions HCO3 HCO3

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 Treatments will be directed at eliminating the cause

Sodium Most abundant in extracellular space Moves among three fluid compartments Found in most body secretions Na Na Sodium Problem is because Na is found is most body fluids Loss of sodium without loss of body fluids, sodium becomes diluted in ECF Vomiting, suctioning, diarrhea, burn, diuretics, SIADH Na Na Na

Hyponatremia – Low Sodium Seizures Personality changes Nausea/vomiting Tachycardia Convulsion Normal Na (135-145) Most common cause is over-hydration with D5W Post-op fluid replacement Heart failure Cirrhosis

Hypernatremia Excessive Na in ECF Loss of water Gain of Sodium Diarrhea Insensible water loss Water deprivation Gain of Sodium Diabetes insipidus Heat stroke 1. Fluid moves outside cell – cells dehydrated Signs and symptoms Dry skin Dry mucus membranes, tongue Low BP Fever CNS - Agitated Restless Lab values – Na high, Urine – high Specific gravity Thirst Causes Diabetic ketoacidosis - Diabetes Insipidus - caused by a lack of response to ADH.  commonly called pituitary DI.   It is also known as central or neurogenic DI.  posterior pituitary can be destroyed by - tumors, infections, head injuries, infiltrations, and various inheritable defects

Hypokalemia – Low Potassium Severe leg cramps Flaccid muscles Fatigue Irregular pulse Chest discomfort EKG changes T wave flattens Normal Potassium-3.5-5 Note - hypokalemia [aLKalosis associated with Low K] Potassium Acquired in the diet Excreted in urine Must be replaced daily Function Maintains acid-base balance Participates in metabolism Causes Poor intake – patient is not eating Renal loss (diuretics) GI loss (diarrhea, vomiting) Signs and symptoms Tachycardia Low BP Flaccid muscles EKG – Flattened T wave Treatment Oral replacement if preferable, could be IV Low K+ could lead to digoxin toxicity due to low circulating volume

Hyperkalemia CNS Peripheral Nervous System Heart Nausea and vomiting Tremors, twitching Heart Bradycardia, peaked T wave Too much Potassium – less common than hypokalemia and More dangerous Common Causes Renal failure (Rarely occurs in person with normal renal function) Signs and symptoms Bradycardia (high K+ suppresses SA node) Tremors, twitching N/V EKG changes – Peaked T, PVC’s, arrhythmias Treat Kayexalate Insulin – pushes K+ back into the little house Dialysis

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 1. Calcium 1. Neuromuscular activity 2. Cardiac activity 3. Blood coagulation Etiology – how does this happen Surgical hypothyroidism Pancratitis Renal failure Vit. D deficiency 3. Signs and Symptoms 1. Hyperactive reflexes 2. Hypotension 3. Positive Trousseaus 4. Positive Chevostek’s 5. Prolonged QT interval Trousseau’s Sign - a test for latent tetany in which carpal spasm is induced by inflating a sphygmomanometer cuff on the upper arm to a pressure exceeding systolic blood pressure for 3 minutes. A positive test may be seen in hypocalcemia and hypomagnesemia. Treatment Oral route is safer IV: calcium gluconate over 5-10 minutes Monitor EKG

Hypercalcemia Causes Signs/symptoms Prolonged immobility Osteoporosis Thiazide diuretics Acidosis Signs/symptoms N/V, weakness Hypoactive reflexes Cardiac arrest Etiology Ca is stored in the bones Essential for neuromuscular activity, cardiac activity, blood coagulation Cause of hypercalcemia Hyperparathyriodism (parathyroids control Ca levels by production of calcitonin Paget’s disease (bone metabolism disease) Excessive Vit. D intake Prolonged immobility Paget's disease is a metabolic bone disease that involves bone destruction and re-growth, which results in deformity. Signs and symptoms Anorexia, N/V Coma Flaccid muscles Arrhythmias and cardiac arrest Treatment Fluids IV aredia, pamidronate

Hypomagnesemia Causes Signs/symptoms Malnutrition Alcoholism Polyuria Pre-ecclampsia Signs/symptoms Muscle tremor Hyperactive deep reflexes Chvostek’s/Trousseau’s Difficulty breathing Magnesium Intracellular reactions and utilization of ATP CNS transmissions Cardiovascular tone Etiology Pancreatitis Cirrhosis GI losses Alcoholism Calcium gluconate administration Treatment of Diabetic ketoacidosis S/S Increased deep tendon reflexes Chvostek’s/Trousseaus signs pos EKG changes Pre-ecclampsia Condition that is not fully understood Occurs in about 8% of pregnancies Symptoms are: high BP, edema in extremities, protein in urine, aches, blurred vision and possible seizures Treat – with Magnesium sulphate IV – acts as vasodialator (causes flushing and hypotension)

Hypermagnesemia Causes Signs/symptoms Renal failure Excessive intake Low BP Muscle weakness Absent reflexes Bradycardia Etiology (not common) Renal disease Hypercalcemia Adrenal insufficiency Signs and symptoms Flushing Low BP, slow pulse Respiratory depression Hypoactive reflexes Increase in Mg depresses skeletal muscles and nerve function Most common cause is renal failure Bradycardia due to depression of acetylcholine Decreased respirations,coma, ECG changes

Respiratory alkalosis pH ↑ PaCO2 ↓ HCO3 ↑ Metabolic acidosis PaCO2 Respiratory acidosis pH ↓ PaCO2 ↑ HCO3 ↓ Respiratory alkalosis pH ↑ PaCO2 ↓ HCO3 ↑ Metabolic acidosis PaCO2 Metabolic alkalosis 1. Respiratory acidosis [more CO2 indicates acidosis] pH - <7.35 PaCO2 – excess CO2 HCO3- low carbonic acid [HCO3 levels are lower than normal indicates acidosis 2. Respiratory alkalosis [more CO2 being exhaled than normal results in alkalosis] pH - > 7.45 PaCO2 – low CO2 HCO3 - high carbonic acid 3. Metabolic acidosis PaCO2 - normal HCO3 – low bicarbonate 4. Metabolic alkalosis HCO3- high bicarbonate

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 – 22 2. pH – 7.32, PaCO2 – 46, HCO3 – 24 3. pH – 7.31, PaCO2 – 35, HCO3 – 20 4. pH – 7.5, PaCO2 – 37, HCO3 - 28 #2 – Because of the retention of CO2, the clinical profile of respiratory acidosis includes decreased pH < 7.35, PaCO# - > 42 with varying levels of HCO3 related to hypoventilation Option #1 is respiratory alkalosis which occur because of blowing off CO2 resulting in decreased level of acid and retention or production of HCO3 resulting in pH > 7.45 Option #3 is Metabolic acidosis because of high H+ or loss of HCO3 often caused by diarrhea, or retention related to kidney failure Option #4 – metabolic alkalosis caused by increased HCO3, or loss of H+, related to vomiting, gastric suction or loss of upper GI secretions

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

Assessment Nursing history Prior Medical History Cancer CVD 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 How do we assess for acid-base balance? Focus on skin, mouth, eyes, cardiovascular system, respiratory system, neurologic, muscular Laboratory tests Serum electrolytes CBC – HCT measures volume of blood that is composed of RBC, affected by changes in volume HCT increases with dehydration – increases with over hydration Serum osmolarity – measures amount of Na, glucose, urea or BUN in blood – increase indicates fluid volume deficit, decrease reflects fluid volume excess Urine pH – acidosis - urine pH should decrease as kidneys secrete H+ ions – metabolic alkalosis pH would increase as kidney retains H+ ions Urine sodium and chloride excretion – indicate renal perfusion Arterial Blood Gases

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 Acute care Education 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