Chapter 42 (3101)

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Chapter 42: Fluids and Electrolytes Fluid surrounds all the cells in the body and is also inside cells. Body fluids contain electrolytes such as sodium and potassium; they also have a certain degree of acidity. Fluid, electrolyte, and acid-base balances within the body maintain the health and function of all body systems. Location and Movement of Water/Electrolytes  Water: 60% body weight; decreases with age. Fluid Distribution  ECF: outside cells; ICF: inside cells.  ICF: 2/3 of total body water; ECF: 1/3 of total body water  ECF: Intravascular(liquid part in blood) and interstitial fluid (between cells and outside blood vessels). Transcellular: cerebrospinal, pleural, peritoneal, and synovial fluids. Composition of Body Fluids  Electrolyte: compound that separates into ions when it dissolves in water. o Cations (pos): NA, K, Ca, Mg. o Anions (neg): Cl, Bicarb.  Osmolality: measure of number of particles per kilogram of water o Tonicity: effective concentration o Isotonic: same as blood o Hypotonic: more dilute than blood o Hypertonic: more concentrated than blood  Active Transport: requires energy in form of ATP to move electrolytes across membrane against concentration gradient (low to high). o Example: Sodium Potassium Pump: moves Na out of cell and K into it, keeping ICF lower in Na and higher in K than ECF.  Diffusion: passive movement of electrolytes or other particles down a concentration gradient (high to low). Diffuse easily by random movements until concentrations is same in all areas. o Require proteins that serve as ion channels. Opening of ion channels: tightly controlled and plays part in muscle and nerve function.  Osmosis: water moves through membrane that separates fluids with different particle concentrations. o Osmotic Pressure: inward pulling force caused by particles in fluid; particles already inside cell exert ICF pressure. Pull water into cell; particles in interstitial fluid exert interstitial fluid osmotic pressure and pull water out of cell.  Filtration: net effect of four forces, two tend to move fluid out of capillaries and small venules and two tend to move fluid back into them. o Hydrostatic Pressure: force of fluid pressing outward against surface.  Colloids: albumin and other proteins in blood o Much larger than electrolytes, glucose, and molecules. o Too large to leave capillaries in fluid that is filtered

o Exert osmotic pressure: Oncotic Pressure: inward pulling force caused by blood proteins that help move fluid from interstitial area back into capillaries. o Capillary Hydrostatic Pressure: strongest at arterial end; fluid moves from capillary into interstitial area, bringing nutrients into cell. Venous end: CHP is weaker and OP is stronger. Fluid moves into venous end capillary, removing wastes. BUN (Blood Urea Nitrogen)  BUN: indicates renal function and hydration status  Normal Range: 10-20mg/dL (slightly higher in older patients); Critical Value: >100mg/dL  Increased BUN: dehydration, excessive protein intake and impaired renal function.  Decreased DUN: overhydration, liver damage, and malnutrition. Hydration  Specific Gravity, Hematocrit (Hct), and Sodium. o Go Up: Fluid Volume Deficit-Dehydration o Go Down: Fluid Volume Excess- Overhydration  Normal Hct: 3 x Hemoglobin (Hgb) (37% Hct)  Hemodilution: 12gm Hgb (27% Hct)  Hemoconcentration: 12gm Hgb (47% Hct) Fluid Balance  Isotonic: no change  Hypotonic: Cell swells  Hypertonic: Cell shrinks Top 5 Fluids  NS 0.9% (NaCl): used to expand volume, dilute medications, and keep veins open.  Lactated Ringer: Fluid resuscitation o NS and LR are ISOTONIC: same osmolarity as body fluid  D5W: HYPOTONIC (iso until inside body-metabolize glucose-become hypo) o DO NOT: give to infants or head injury patients: Causes cerebral edema.  D5 ½ NS (D5NS): Sodium and volume replacement: HYPERTONIC o Go slow! Monitor BP, pulse, quality of lung sounds, and urine output. Fluid Balance  Maintain fluid balance: fluid intake = fluid output. o Normal daily fluid output (e.g., urine, sweat) is a hypotonic salt solution, people must have equal fluid intake of hypotonic sodium-containing fluid (or water plus foods with some salt) to maintain fluid balance.  Fluid Intake: Orally through drinking and eating (most foods contain some water) o Food metabolism creates additional water. o Average fluid intake: 2300 mL o Other routes of fluid intake: intravenous (IV), rectal (e.g., enemas), and irrigation of body cavities that can absorb fluid.  Fluid Distribution: movement of fluid among its various compartments.

o Movement of fluid among various compartments. o Fluid distribution between the extracellular and intracellular compartments occurs by osmosis. o Fluid distribution between the vascular and interstitial portions of the extracellular fluid (ECF) occurs by filtration.  Fluid Output: skin, lungs, GI tract, kidneys. o Waste products of metabolism: to liver as ammonia, breaks down nitrogen, goes out hepatic vein, and to kidneys as urea released from liver. o 3-6 L of fluid moves into the GI tract daily and then returns again to the ECF. o Normal Excretion: 100 mL of fluid each day through feces o Skin, lungs, GI tract, and kidneys. Abnormal: vomit, drainage, or hemorrhage.  Insensible loss: skin and lungs; increases when person has fever or recent burn on skin  Sweat: visible and contains Na; increases output  GI: 3-6L into GI tract daily and returns to ECF.  Kidneys: Respond to hormone that influence urine production. o Kidneys: respond to hormones that influence urine production.  Drink more water; increase urine production to maintain fluid balance.  Drink less water, sweat a lot, or lose fluid by vomiting; urine volume decreases to maintain fluid balance. o Antidiuretic Hormone: regulates the osmolality of the body fluids by influencing how much water is excreted in urine.  Synthesized by neurons in the hypothalamus that release it from the posterior pituitary gland.  ADH circulates in the blood to the kidneys, where it acts on the collecting ducts.  Renal cells to resorb water, taking water from renal tubular fluid and putting back in blood; decreases urine volume.  More ADH is released if body fluids become more concentrated.  Factors that increase ADH levels include severely decreased blood volume (e.g., dehydration, hemorrhage), pain, stressors, and some medications.  ADH levels decrease if body fluids become too dilute; allows more water to be excreted in urine. o Renin-Angiotensin-Aldosterone System: regulates ECF volume by influencing how much sodium and water are excreted in urine.  Contributes to regulation of blood pressure.  Specialized cells in kidneys release the enzyme renin (acts on angiotensinogen- inactive protein secreted by liver that circulates in blood)  Renin converts angiotensinogen to angiotensin I, then convert to angiotensin II.  Angiotensin II: vasoconstriction; stimulation of aldosterone release.  Aldosterone: circulates to the kidneys, where it causes resorption of sodium and water in isotonic proportion in the distal renal tubules.  Contributes to electrolyte and acid base balance by increasing urinary excretion of potassium and hydrogen ions.  Removing sodium and water from the renal tubules and returning it to the blood increases the volume of the ECF.

o Atrial Natriuretic Peptide: regulates ECV by influencing how much sodium and water are excreted in urine.  Cells in the atria of the heart release ANP when they are stretched (e.g., by an increased ECV).  ANP: weak hormone that inhibits ADH by increasing the loss of sodium and water in the urine (see Fig. 42-6, C).  ANP opposes the effect of aldosterone. Thirst  Important regulator of fluid intake when plasma osmolality increase; conscious desire for water.  Thirst control is located in hypothalamus.  Thirst-Control Mechanism o Increase plasma osmolality: osmoreceptor-mediated thirst. o Angiotensin II: baroreceptor-mediated thirst and angiotensin II o Angiotensin III: baroreceptor-mediated thirst and angiotensin III o Dry pharyngeal mucous membranes o Decreased plasma volume o Psychological factors Imbalance and Related Causes Signs and Symptoms Isotonic Imbalances: water and sodium loss of gained in equal or isotonic proportions. Extracellular FVD: body fluids have decreased volume but normal osmolality  Sodium and water intake less than output, causing isotonic loss.  Severely decreased oral intake of water and salt.  Increase GI output: vomit, diarrhea, laxatives, overuse, of drainage.  Increased renal output: diuretics, adrenal insufficiency.  Loss of blood of plasma: burns or hemorrhage.  Massive sweating without intake.  Sudden weight loss, postural hypotension, tachycardia, thready pulse, dry mucous membranes, poor skin turgor, slow vein filling, and dark urine.  Severe: thirst, restlessness, confusion, oliguria, cold skin, and hypovolemic shock.  Labs: increase Hct, Increased BUM, and Increased specific gravity. Extracellular FVE: body fluids have increased volume but normal osmolality  Sodium and water intake greater than output, causing isotonic gain.  Excessive admin of Na.  Renal retention of Na and water: heart failure, cirrhosis, aldosterone excess, or renal disease.  Sudden weight gain, edema, crackles in lungs.  Severe: confusion, and pulmonary edema.  Labs: decreased Hct, BUN, and gravity. Osmolality Imbalances Hypernatremia: Water Deficit: Body Fluids Too Concentrated  Loss of more water than salt  Diabetes (ADH deficit)  Large perspiration and respiratory water output without intake  Gain of more salt than water  Admin of tube feedings, TPN, lack of access to water, and dysfunction of  Decreased level of consciousness, thirsts, seizures  Labs: increased Na levels and osmolality.

osmoreceptor driven thirst drive. Hyponatremia: Water Excess: Fluids too Dilute  Gain of more water than salt: excessive ADH, excessive water intake, excessive IV admin, enemas.  Loss of more salt than water: replacement of large output (diarrhea and vomit).  Decreased level of consciousness, seizures.  Labs: decreased Na and osmolality levels. Combines Volume and Osmolality Imbalance Clinical Dehydration (ECV Deficit + Hypernatremia): Body Fluids Have Decreased Volume and Are Too Concentrated  Sodium and Water Intake Less than Output, with Loss of More Wate than Salt: poor water intake and ECV deficit.  ECV plus hypernatremia. Fluid Imbalances  Anything disrupts fluid intake/output (disease, meds, factors): imbalances. o Example: diarrhea: fluid output is increased; fluid imbalance (dehydration) occurs if fluid intake does not increase.  Two major types of fluid imbalances: Volume Imbalances and Osmolality Imbalances. o Volume imbalances: disturbances of the amount of fluid in the extracellular compartment. o Osmolality imbalances: disturbances of the concentration of body fluids.  Volume Imbalances o Extracellular fluid volume (ECV) imbalance: too little (ECV deficit) or too much (ECV excess) isotonic fluid is present.  ECV deficit and excess are abnormal volumes of isotonic fluid (sudden changes in body weight and changes in markers of vascular and interstitial volume).  ECV deficit is present: isotonic fluid is insufficient in the extracellular compartment.  ECV deficit: output of isotonic fluid exceeds intake of sodium-containing fluid (ECF is both vascular and interstitial); signs and symptoms arise from lack of volume.  ECV excess: too much isotonic fluid is found in the extracellular compartment.  Intake of sodium-containing isotonic fluid has exceeded fluid output.  Eat more salty foods: ankles swell or rings on your fingers feel tight and weight gain.  Osmolality Imbalances o Body fluids become hypertonic or hypotonic: osmotic shifts of water across cell membranes. o Osmolality imbalances: hypernatremia and hyponatremia.  Hypernatremia (water deficit): hypertonic condition.  Loss of relatively more water than salt, or gain of relatively more salt than water.  Interstitial fluid becomes hypertonic: water leaves cells by osmosis, and they shrivel.  SS: cerebral dysfunction, which arise when brain cells shrivel.  Hyponatremia (water excess): hypotonic condition.

 Gain of more water than salt or loss of relatively more salt than water.  Causes: water to enter cells by osmosis, causing the cells to swell.  SS: cerebral dysfunction occur when brain cells swell. Electrolyte Intake/Absorption/Distribution/Output Electrolyte Intake/Absorption Distribution Output Function Potassium (K)  Fruits, potatoes, coffee, molasses, nuts.  Absorbs easily  Low in ECF, high in ICF  Insulin, epinephrine, and alkalosis shift K into cells.  Aldosterone, black licorice, hypomag, and polyuria, increased renal excretion.  Acute diarrhea  Maintains resting membrane potential of skeletal, smooth, and cardiac muscle, allowing normal muscle function Calcium (Ca)  Dairy, fish, broccoli, oranges.  Vitamin D for absorption.  Undigested fats prevent absorption.  Low in ECF (bones and intra)  Some in blood is bound and inactive.  Parathyroid hormone shifts Ca out of bone; calcitonin shift into bone.  Thiazide diuretics  Chronic diarrhea and undigested fat.  Influences excitability of nerve and muscle cells; necessary for muscle contraction Magnesium (Mg)  Dark leak greens, whole grains, antacids  Undigested fats prevent absorption  Low in ECF  Some in blood is bound and inactive  Risin blood ethanol  Oliguria  Chronic diarrhea.  Influences function of neuromuscular junctions; is a cofactor for numerous enzymes Phosphorus (Ph)  Milk, processed foods.  Aluminum antacids prevent absorption.  Low in ECF and high in ICF  Insulin and epinephrine shift Ph into cells  Oliguria and elevated fibroblasts growth  Necessary for production of ATP, the energy source for cellular metabolism Electrolyte Balance  Factors cause Electrolyte Imbalance: diarrhea, endocrine disorders, and medications.  Intake and Absorption

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