Imbalances Of: Fluids, Electrolytes, & Acid-bases Pathophysiology

Review of Body Fluids Fluid compartments Body Water Healthy adult Male = 60% Female = 50% Babies = 75% Elderly = 45% Calculation: 1 Kg = 1 L water volume 150# = 70Kg 60% of 70Kg = approx 40Kg 40Kg = 40L Fluid compartments 2 main ones ICF = 2/3 volume of fluid in body ECF = 1/3 volume of fluid in body Plasma = 20% Interstitial fluid = 80% Calculation: 40L = fluid volume 2/3 = 25L of ICF 1/3 = 15L of ECF NB: Blood = 3-4% of weight

Solution = Solute + Solvent Solution = the fluid compartment (ICF or ECF) Solvent = water Solutes: Electrolytes Charged ions They dissolve in water They can conduct an electric current Major cations: ECF = sodium ICF = potassium Major anions: ECF = chloride, bicarbonate ICF = proteins w/ neg charge Non-electrolytes Polar =those that are water soluble (sugars, proteins) Non-polar = those that are water insoluble (lipids)

Basic concepts relating to regulation of fluid & electrolytes Water moves passively in response to changes in solute concentration Key = water follows salt Thus, regulation of fluid balance & electrolyte balance are intertwined All monitors to homeostatic balance occur in ECF and not ICF !! Fluid shifts occur between ICF & ECF in response to changes only in ECF Key to equilibrium is maintaining solute concentration (osmolality = # solute particles in one liter of solution & is the ability of that solution to cause osmosis) between ICF & ECF If change to hypertonic ECF, then water into ECF If change to hypotonic ECF, then water into ICF During transfer on nutrients (chemicals) an average 24 liters of fluid moves out of plasma each day; 85% is reabsorbed & the remainder (4L) is the lymph fluid that accumulates At the capillary level have 2 separate forces at work: Hydrostatic pressure --- pushes fluid out of vessels Colloid osmotic pressure --- pushes fluid into vessels See Next Slide

Note: Insensible loss = 1000 cc/day Fluid balance Important in IV daily maintenance Intake & output ( I &O ) Note: Insensible loss = 1000 cc/day

The control of fluid balance What is monitored: Volume & Osmolality (osmotic pressure via solute conc.) Mechanisms: ADH (antidiuretic hormone) , osmoreceptors, & thirst mechanism Osmoreceptors in hypothalamus regulates secretion of ADH from posterior pituitary The higher the osmolality, the more ADH secreted ADH causes: (1) thirst center to be stimulated (2) kidneys to conserve water Aldosterone Secreted by adrenal cortex Causes kidneys to retain sodium (nb: water follows salt) Stimulated by: increase potassium, falling sodium, & renin-angiotensin Atrial natriuretic peptide (ANP) Released by distended atrial walls of heart Secretion caused by increased pressure and/or volume Antagonistic to aldosterone

Fluid Excess --- Edema Edema = excessive amount of fluid in interstitial compartment 4 main causes Increased capillary hydrostatic pressure Etiology Hypertension Increased blood volume ---- 2o to pregnancy, renal failure, CHF Loss of plasma proteins (esp. albumin) Kidney disease, malnutrition, malabsorption Obstruction of lymphatic circulation Cancer, parasitic diseases, post surgical Increased capillary permeability Inflammation, toxins, burns see next slide

Effects of edema Swelling------- local or generalized Pitting edema Increase in body weight Functional impairment Pain impaired arterial circulation (obesity) Pressure exerted on arteries

Fluid deficiency --- Dehydration Loss is generally from ECF Mild dehydration = decrease of 2% in body weight Moderate dehydration = 5% loss of body weight Severe dehydration = 8% loss Loss of water usually accompanied by loss of electrolytes Remember water follows salt But can get 3 types of dehydration (1) Isotonic dehydration = equal loss of fluid & lytes (2) Hypotonic dehydration = loss of more lytes than water (3) Hypertonic dehydration = loss of more fluid than lytes Causes Vomiting & diarrhea, N-G suction Excess sweating Diabetic ketoacidosis Insufficient water intake

Effects of dehydration Dry mucous membranes Decreased skin turgor Decreased BP Increased hematocrit Compensatory mechanisms Increase thirst Increase pulse Constriction of vessel to skin Get pale, cool skin Decreased urine output If brain cells lose water, can get confusion, unconsciousness, & coma “ downer” Diagnose dehydration: Dry tongue Poor skin turgor Concentrated urine

Electrolytes & Their Imbalances Sodium (Na+) Sodium balance Sodium = major cation in extracellular fluid (ECF) Sodium = most common problem with electrolyte balance Key to balance: ingestion via G-I tract = excretion via kidney Aldosterone controls sodium levels via the kidney Remember aldosterone’s antagonist = ANP Sodium contributes to resting membrane potential Sodium rushing into cell via open channels causes depolarization of nerves and muscles

Signs of sodium imbalance hyponatremia hypernatremia Weakness & fatigue weakness & agitation G-I: anorexia, nausea, cramps G-I: thirst, dry mucosa Hypotension hypertension & edema Mental confusion & ? Seizures (from fluid shift into brain cells) Causes of hyponatremia Excess sweating, vomiting, diarrhea Diuretics Renal failure Excess water intake (water intoxication) Hormonal imbalances Causes of hypernatremia Watery diarrhea Long periods of rapid respiration Loss of thirst mechanism

Electrolytes & Their Imbalances Potassium (K+) Potassium balance Major intracellular cation Balance: ingestion = excretion (via kidneys) Aldosterone primarily controls potassium It exchanges potassium for sodium Insulin also regulates potassium It drives it into cells (with sugar) & thus produces hypokalemia pH also affects potassium secretion Acidosis: more H+ in blood which finds its way into cell & pushes K+ into blood Also get kidney to exchange H+ for K+ Acidosis -gives- hyperkalemia Alkalosis: less H+ in blood Kidneys exchange K+ for H+; thus get hypokalemia

Effects of abnormal potassium on cardiac function Hyperkalemia = fast repolarization; heart gets more irritable Hypokalemia = cell can’t repolarize & heart gets less irritable Effects of hyper & hypokalemia very similar Both give: Muscle weakness, & paresthesias Nausea Kidney effects: Hyperkalemia : oliguria, retention of H+ (become acidotic) Note: oliguria because of aldosterone secretion Hypokalemia : polyuria, excretion of H+ (become alkalotic) Note: polyuria because of decrease aldosterone secretion

Electrolytes & Their Imbalances Calcium (Ca++) Calcium balance Calcium is most abundant mineral in body Calcium is important as an extracellular cation Calcium & phosphorus have a reciprocal relationship Calcium balance is dependent on: Parathyroid hormone (PTH) Calcitriol (active vitamin D) Calcitonin (from thyroid) 98% of calcium reabsorbed at the kidneys Calcium functions Structural strength for bones & teeth Maintains stability of nerve membrane Required for muscle cell contraction Necessary for blood clotting

Hypercalcemia Hypocalcemia Symptoms Symptoms Tetany SOUP Causes Hyperparathyroidism Most frequent cause Malignant tumors Immobility Via demineralization Milk- alkali syndrome Effects General muscle weakness Increase strength of heart muscle contraction !! Prevention of ADH working on the kidney Increase in PTH leads to decrease bone density Hypocalcemia Symptoms Tetany Weak heartbeat Muscle spasms Convulsions Causes Not too common Renal failure Malabsorption Alkalosis Effects Low calcium leads to increased membrane permeability of nerves & get spontaneous stimulation of skeletal muscle (tetany) Weakens muscle cell contraction Thus weak heart contraction [note opposite effects on skeletal & cardiac m.]

Other Electrolytes & Their Imbalances Magnesium Imbalances are rare Most is reabsorbed by kidneys Chloride Primarily in ECF 99% reabsorbed in normal adult Usually follows sodium Note: chloride-bicarbonate shift with vomiting Phosphate Works primarily in ICF for formation of ATP & cell membranes

Physiology of acid-base balance Acid-Base Imbalance Physiology of acid-base balance Changes in pH Disrupt the stability of cell membrane Alters protein Alter protein structure Alter enzyme activity Normal = 7.34 – 7.45 Acidosis more common & clinically more significant Remember that metabolic acids are by-products of metabolism Acidosis if pH < 7.35 Clinical findings Coma develops Cardiac muscle deteriorates Peripheral vasodilation (decrease BP) Weak vs. strong acids Strong acids dissociate in solution freeing up more hydrogen ions Weak acids enter a solution & a significant number of molecules remain intact

Buffer systems are used to keep the body in pH balance (homeostasis) It consists of a weak acid (H+)and its dissociation products (an anion) 3 major buffer systems in human [1] Protein buffer system (includes hemoglobin buffer system) Regulates ICF & ECF (both plasma & interstitial fluid) Most important in ICF & hemoglobin Hemoglobin buffer system = carbonic anhydrase in RBC * it absorbs CO2 from ECF & get immediate effect Amino acids have carboxyl group (gives up H+) and Amino acids have amino group(can accept H+)

[2] Carbonic acid-bicarbonate buffer system Important in ECF Lots of carbon dioxide from metabolic acids It mixes with water & get carbonic acid which dissociates into H+ & HCO3- Metabolic acids have H+ ; Our body has “bicarbonate reserve” Bicarbonate reserve = ample supply of bicarb in ECF These combine to form CO2 + H2O CO2 excreted via lungs Think of CO2 as an acid since it readily combines with water to become carbonic acid

Note: Blood (hemoglobin) acts first Works on excess H+ Kidneys act secondly Rids one of excess H+ Lungs act last Rids one of excess HCO3-

Lung’s mechanism to regulate body’s pH

Summary of 3 key buffer systems [3] Phosphate buffer system Important in ICF Phosphate is an anion but a weak acid Summary of 3 key buffer systems Hemoglobin buffer system (protein) --- short term Carbonic acid buffer system ---- long term Phosphate buffer system

To maintain acid- base balance you must control hydrogen ion losses & gains 3 key ways: This is done by (1) pulmonary & (2) renal mechanisms These are called metabolic buffer systems Also done by (3) buffer systems These are called chemical buffer systems:

Imbalances of pH ------ 4 basic categories

Key points Excess vomiting = loss of acid & get metabolic alkalosis Excess diarrhea = loss of bicarbonate & get metabolic acidosis Sx of acidosis = CNS depression Sx of alkalosis = CNS irritability Both acidosis & alkalosis will lead to coma